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Tenkara rods
Tenkara rods are a type of bamboo fly rod used for tenkara fishing in Japan. A mixture of the rods in the other categories, they are carbon rods, fly rods and telescopic rods all in one. These are ultra-light and very portable telescopic rods (read more about telescopic below). Their extended length normally ranges from , and they have a very soft action. The action of tenkara rods has been standardized as a ratio of "how many parts are stiffer : how many tip parts bend more easily". The standard actions are 5:5, 6:4, 7:3, and 8:2, with 5:5 being a softer/slower rod, and 8:2 being a stiffer rod. Similar to western fly-rods tenkara rods also have cork, and sometimes even wooden handles, with wooden handles (such as red-pine, and phoenix-tree wood) being the more prized rods due to their increased sensitivity to fish bites and the heavier feel that helps balance the rods. Tenkara rods have no guides. Tenkara is a fixed-line fishing method, where no reel is used, but rather the line is tied directly to the tip of the rod. Like the carbon rods mentioned above this allows for "very precise positioning of the fly which in turn enables huge catches of fish with accurate feeding". One of the most common flies used in tenkara fishing is the Sakasa Kebari. Tenkara fishing is very popular in Japan, where these rods can be found in every major tackle shop. In the US, tenkara is beginning to grow in popularity.
Spin casting rods
Spin casting rods are rods designed to hold a spin casting reel, which are normally mounted above the handle. Spin casting rods also have small eyes and, frequently, a forefinger grip trigger. They are very similar to bait casting rods, to the point where either type of reel may be used on a particular rod. While rods were at one time offered as specific "spin casting" or "bait casting" rods, this has become uncommon, as the rod design is suited to either fishing style. Today they are simply called "casting rods", and are usually offered with no distinction as to which style they are best suited for in use. | Fishing rod | Wikipedia | 464 | 47337 | https://en.wikipedia.org/wiki/Fishing%20rod | Technology | Hunting and fishing | null |
Baitcasting rods
While the easy to use spin casting rods are often used by novice anglers, baitcasting rods and reels are generally more difficult to use. Professional anglers, however, prefer baitcasting rod and reel combos because baitcasting reels grant anglers more accuracy in their casts. Casting rods are typically viewed as somewhat more powerful than their spinning rod counterparts – they can use heavier line and can handle heavier cover. Baitcasting rods low profile design along with a super silent high-speed 7.0:1-line retrieve.
Spinning rods
Spinning rods are made from graphite or fiberglass with a cork or PVC foam handle, and tend to be between in length. Typically, spinning rods have anywhere from 5–8 guides arranged along the underside of the rod to help control the line. The eyes decrease in size from the handle to the tip, with the one nearest the handle usually much larger than the rest to allow less friction as the coiled line comes off the reel, and to gather the very large loops of line that come off the spinning reel's spool. Unlike bait casting and spin casting reels, the spinning reel hangs beneath the rod rather than sitting on top, and is held in place with a sliding or locking reel seat. The fisherman's second and third fingers straddle the "leg" of the reel where it is attached to the reel seat on the rod, and the weight of the reel hangs beneath the rod, which makes for a more comfortable way to fish for extended periods. This also allows the rod to be held in the fisherman's dominant hand (the handle on most modern spinning reels is reversible) which greatly increases control and nuance applied to the rod itself. Spinning rods and reels are widely used in fishing for popular North American sport fish including bass, trout, pike and walleye. Popular targets for spinning in the UK and European continent are pike, perch, eel and zander (walleye). Longer spinning rods with elongated grip handles for two-handed casting are frequently employed for saltwater or steelhead and salmon fishing. Spinning rods are also widely used for trolling and still fishing with live bait. | Fishing rod | Wikipedia | 446 | 47337 | https://en.wikipedia.org/wiki/Fishing%20rod | Technology | Hunting and fishing | null |
Ultra-light rods
These rods are used to fish for smaller species, they provide more sport with larger fish, or to enable fishing with lighter line and smaller lures. Though the term is commonly used to refer to spinning or spin-cast rods and tackle, fly rods in smaller line weights (size #0–#3) have also long been utilized for ultra-light fishing, as well as to protect the thin-diameter, lightweight end section of leader, or tippet, used in this type of angling.
Ultra-light spinning and casting rods are generally shorter ( is common) lighter, and more limber than normal rods. Tip actions vary from slow to fast, depending upon intended use. These rods usually carry test fishing line. Some ultra-light rods are capable of casting lures as light as – typically small spinners, wet flies, crappie jigs, tubes, or bait such as trout worms. Originally produced to bring more excitement to the sport, ultra-light spin fishing is now widely used for crappie, trout, bass, bluegill, roach, perch, bream, pumpkin-seed, tench and other types of pan fish.
Ice rods
Modern ice rods are typically very short spinning rods, varying between in length. Classic ice rods – still widely used – are simply stiff rod-like pieces of wood, usually with a carved wooden handle, a couple of line guides, and two opposing hooks mounted ahead of the handle to hand-wind the line around. Ice rods are used to fish through holes in the cover ice of frozen lakes and ponds.
Sea rods
Sea rods are designed for use with fish from the ocean. They are long, (around on average), extremely thick, and feature huge and heavy tips, eyes, and handles. The largest of sea rods are for use with sport fishing boats. Some of these are specialized rods, including shark rods, and marlin rods, and are for use with very heavy equipment. | Fishing rod | Wikipedia | 398 | 47337 | https://en.wikipedia.org/wiki/Fishing%20rod | Technology | Hunting and fishing | null |
Surf rods
The most common type of sea rods are for surf casting. Surf casting rods resemble oversized spinning or bait casting rods with long grip handles intended for two-handed casting techniques. Generally between in length, surf casting rods need to be longer in order for the user cast the lure or bait beyond the breaking surf where fish tend to congregate, and sturdy enough to cast heavy weighted lures or bait needed to hold the bottom in rough water. They are almost always used in shore fishing (sea fishing from the shoreline) from the beach, rocks or other shore feature. Some surfcasters use powerful rods to cast up to or more of lead weight, artificial lures, and/or bait over .
Trolling rods
Trolling is a fishing method of casting the lure or bait to the side of, or behind, a moving boat, and letting the motion of the boat pull the bait through the water. In theory, for light and medium freshwater gamefishing, any casting or spinning rod (with the possible exception of ultralight rods) can be used for trolling. In the last 30 years, most manufacturers have developed a complete line of generally long, heavily built rods sold as "Trolling Rods", and aimed generally at ocean anglers and Great Lakes salmon and steelhead fishermen. A rod effective for trolling should have relatively fast action, as a very "whippy" slow action rod is extremely frustrating to troll with, and a fast action (fairly stiff) rod is generally much easier to work with when fishing by this method. Perhaps the extreme in this philosophy was reached during the 1940s and early 1950s, when the now-defunct True Temper corporation – a maker of garden tools – marketed a line of trolling rods of length made of tempered steel which were square in cross section. They acted as excellent trolling rods, though the action was much too stiff for sportsmanlike playing of fish once hooked. As Great Lakes sportfishing in particular becomes more popular with each passing year, all rod manufacturers continue to expand their lines of dedicated "trolling" rods, though as noted, for most inland lake and stream fishing, a good casting or spinning rod is perfectly adequate for trolling.
Telescopic rods | Fishing rod | Wikipedia | 447 | 47337 | https://en.wikipedia.org/wiki/Fishing%20rod | Technology | Hunting and fishing | null |
Telescopic fishing rods are designed to collapse down to a short length and open to a long rod. rods can close to as little as . This makes the rods very easy to transport to remote areas or travel on buses, compact cars, or public buses and subways. Telescopic fishing rods are made from the same materials as conventional multi-piece rods. Graphite, carbon, and sometimes fibreglass, or composites of these materials, are designed to slip into each other so that they open and close. The eyes on the spinning rods are generally, but not always, a special design to aid in making the end of each section stronger. Various grade eyes available in conventional rods are also available in telescopic fishing rods. The eyeless Tenkara style rods are also of this type and are typically made from carbon and/or graphite.
Care for telescopic fishing rods is much the same as other rods. The only difference being that one should not open the telescopic rod in manner that whips a closed rod into the open position rapidly. Whipping or flinging a telescopic fishing rod open may and likely will cause it to be difficult to close. When closing the rods make a slight twisting motion while pushing the sections together. Often the rods come with tip covers to protect the tip and guides. Additionally, extra care must be taken not to get dirt or sand in the joints; due to their design this can easily damage this style of rod.
Telescopic rods are popular among surf fishermen. Carrying around a surf fishing rod, even in two pieces, is cumbersome. The shorter the sections the shorter they close, the more eyes they have, and the better the power curve is in them. More eyes means better weight and stress distribution throughout the parabolic arc. This translates to further casting, stronger fish fighting abilities, and less breaking of the rod. | Fishing rod | Wikipedia | 381 | 47337 | https://en.wikipedia.org/wiki/Fishing%20rod | Technology | Hunting and fishing | null |
A fishing reel is a hand-cranked reel used in angling to wind and stow fishing line, typically mounted onto a fishing rod, but may also be used on compound bows or crossbows to retrieve tethered arrows when bowfishing.
Modern recreational fishing reels usually have fittings aiding in casting for distance and accuracy, as well as controlling the speed and tension of line retrieval to avoid line snap and hook dislodgement. Fishing reels are traditionally used in angling and competitive casting. They are typically attached near the handle of a fishing rod, though some specialized reels with pressure sensors for immediate retrieval are equipped on downrigger systems which are mounted directly to an ocean-going sport boat's gunwales or transoms and are used for "deep drop" and trolling.
The earliest fishing reel was invented in China at least since the Song dynasty, as shown by detailed illustration of an angler fishing with reel from Chinese paintings and records beginning about 1195 AD, although sporadic textual descriptions of line wheels used for angling had existed since the 3rd century. These early fishing reel designs were likely derived from winches/windlasses and roughly resemble the modern centerpin reels.
Fishing reels first appeared in the Western Hemisphere in England around 1650 AD. An incident is disclosed in an excerpt from author Thomas Barker found in his book, The Art of Angling: wherein are discovered many rare secrets, very necessary to be knowne by all that delight in that recreation:
In the 1760s, London tackle shops were advertising multiplying or gear-retrieved reels. The first popular American fishing reel appeared in the United States around 1820. During the second half of the 20th century, Japanese and Scandinavian reel makers such as Shimano, Daiwa and ABU Garcia, previously all precision engineering manufacturers for biking equipments and watchmaking, began rising to dominate the world market.
History
Origins in China | Fishing reel | Wikipedia | 388 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
In literary records, the earliest evidence of the fishing reel comes from a 3rd-century AD Chinese work entitled Lives of Famous Immortals, where the term "angling lathe" (釣車) was used. Tang dynasty poet Lu Guimeng (?–881) and his friend Pi Rixiu (834–883), both avid anglers, frequently mentioned "angling lathe" and "angle-fishing wheel" (釣魚輪) in their fishing poems, with Pi even describing a gift reel he received as "an angle-handled wheel [that] is smooth and light" (角柄孤輪細膩輕). Song dynasty poets, such as Huang Tingjian (1045–1105) and Yang Wanli (1127–1206), also made reference to "angling lathe" in lyrics involving lakes and fishing boats. Northern Song scientist Shen Kuo (1031–1095) even once wrote in a travel book that "angling uses wheeled rod, rod uses purple bamboo, the wheel is not to be large, the rod shouldn't be long, but [you] can angle if the line is long" (釣用輪竿，竿用紫竹，輪不欲大，竿不宜長，但絲長則可釣耳).
The earliest known graphical depiction of a fishing reel, according to Joseph Needham, comes from a Southern Song (1127–1279) painting done in 1195 by Ma Yuan (c. 1160–1225) called "Angler on a Wintry Lake". The painting, currently in collection at Tokyo National Museum after the looting of the Old Summer Palace, showing a man sitting on a small sampan boat while casting out his fishing line. Another fishing reel was featured in a painting by Wu Zhen (1280–1354). The book Tianzhu lingqian (Holy Lections from Indian Sources), printed sometime between 1208 and 1224, features two different woodblock print illustrations of fishing reels being used. An Armenian parchment Gospel of the 13th century shows a reel (though not as clearly depicted as the Chinese ones). The Sancai Tuhui, a Chinese encyclopedia published in 1609, features the next known picture of a fishing reel and vividly shows the windlass pulley of the device. These five pictures are the only ones which feature fishing reels before the year 1651.
Development in England | Fishing reel | Wikipedia | 502 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
The first English book on fishing is "A Treatise of Fishing with an Angle" in 1496 (its spelling respective to the manner of the date is The Treatyse of Fysshynge with an Angle'). However, the book did not mention a reel. A primitive reel was first cited in the book The Art of Angling by Thomas Barker (fl.1591–1651), first published in 1651. Fishing reels first appeared in England around the 1650s, a time of growing interest in fly fishing.
The fishing industry became commercialized in the 18th century, with rods and tackle being sold at the haberdashers store. After the Great Fire of London in 1666, artisans moved to Redditch, a center of fishing-related products from the 1730s. Onesimus Ustonson established his trading shop in 1761, and his establishment remained a market leader for the next century. He received a Royal Warrant from three successive monarchs, starting with King George IV.
Some have credited Onesimus with the invention of the fishing reel – he was undoubtedly the first to advertise its sale. Early multiplying reels were wide and had a small diameter, and their gears, made of brass, often wore down after extensive use. His earliest advertisement in the form of a trading card dates from 1768 and was entitled To all lovers of angling. A full list of the tackles he sold included artificial flies and 'the best sort of multiplying brass winches both stop and plain.' The commercialization of the industry came at a time of expanded interest in fishing as a recreational hobby for members of the aristocracy.
Modern reel design began in England during the latter part of the 18th century, and the predominant model in use was known as the 'Nottingham reel'. The reel was a wide drum that spooled out freely, and was ideal for allowing the bait to drift along way out with the current.
Tackle design began to improve from the 1880s. The introduction of new woods to the manufacture of fly rods made it possible to cast flies into the wind on silk lines, instead of horse hair. These lines allowed for a much greater casting distance. A negative consequence of this, was that it became easy for the much longer line to get into a tangle. This problem spurred the invention of the regulator to evenly spool the line out and prevent tangling. | Fishing reel | Wikipedia | 480 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Albert Illingworth, 1st Baron Illingworth a textiles magnate, patented the modern form of fixed-spool spinning reel in 1905. When casting Illingworth's reel design, the line was drawn off the leading edge of the spool, but was restrained and rewound by a line pickup, a device which orbits around the stationary spool. Because the line did not have to pull against a rotating spool, much lighter lures could be cast than with conventional reels.
Development in the United States
Geared multiplying reels failed to gain traction in Britain but had more success in the United States, where English models were modified by George W. Snyder (c.1780–1841), a skillful watchmaker and silversmith in Paris, Kentucky, into his own bait-casting reel named the Kentucky Reel, the first American-made design in 1810. Snyder's first reel was made for his own angling use, but afterward, he made reels for members of his club. Without patent or trademark protection, Snyder's Kentucky Reel was quickly copied by many others, including Meek, Milam, Sage, Hardman and Gayle. These artisans were trained in jewelry fabrication and were experienced in cutting gears, constructing small parts, and doing precision work. In time, the Kentucky Reel was mass-produced by the emerging factories located in the Northeast, where they could be produced at a fraction of the cost and time required for hand-built construction. The availability of more affordable fly reels greatly stimulated the sales and popularity of fly fishing equipment. It was soon applied to bait casting reels, resulting in a surge in the popularity of fishing as a pastime among all levels of American society.
The American, Charles F. Orvis, designed and distributed a novel reel and fly design in 1874, described by reel historian Jim Brown as the "benchmark of American reel design," and the first fully modern fly reel. The founding of The Orvis Company helped institutionalize fly fishing by supplying angling equipment via the circulation of his tackle catalogs, distributed to a small but devoted customer list. | Fishing reel | Wikipedia | 429 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Types
Fishing reels can be classified into two design groups: rotary-spool and fixed-spool. Rotary-spool designs are essentially similar to a spinning wheel or windlass, where the spool actively rotates to wind the line around itself. Fixed-spool designs, on the other hand, behave like a spindle and have no rotating motion of the spool, instead using a separate spinning mechanism that revolves around the spool to drag and wrap the line around onto the spool.
Rotary-spool
Rotary-spool reels can be further subdivided into two types: single-action and multiplier. Single-action reels have a synchronous rotating action between the crank handle and the spool (hence the name, "single[-ratio] action"), and quite often the handle is mounted directly on the spool frame (in which case, the spool frame itself becomes the crank). Multiplier reels, on the other hand, have an internal gear train design that amplifies the number of spool turns for every turn of the crank handle, allowing much faster line retrievals. The spool on multiplier reels also spins in the opposite direction to that of single-action spools.
With larger-capacity spools (typically in multiplier reels), there is usually a slider mechanism in front of the spool – known as the line guide — that pushes the line side-to-side in an oscillating motion, which allows the line winding to be more evenly distributed across the spool instead of bunching up at one section.
Centrepin reel | Fishing reel | Wikipedia | 339 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
The centrepin reel (or centerpin, center pin, or float reel) is a single-action reel which runs freely enough on its axle ("centrepin"). The centrepin reel is the earliest fishing reel design invented by humans, and is historically and currently used for coarse fishing. Instead of a mechanical drag, the angler's thumb is typically used to control the fish. Fishing in the margins for carp or other heavy fish with relatively light tackle is very popular with a 'pin' and is often used for 'trotting' a method in which a float on the line suspends a bait a certain depth to flow with the current along the waterway. During the 1950s and 1960s, many anglers in England began fishing with a centrepin reel. Despite this, the centrepin is today mostly used by coarse anglers, who remain a small proportion of the general fishing population.
A special class of centrepin reel known as the fly reel, used specifically for fly fishing, is normally operated by manually stripping the line off the reel with one hand, while casting the rod with the other hand. The main purpose of a fly reel is to help cast ultralight fly lures and provide smooth uninterrupted tension (drag) when a fish makes a long run, and counterbalance the weight of the fly rod when casting. When used in fly fishing, the fly reel or fly casting reel has traditionally been rather simple in terms of mechanical construction, and little has changed from the design patented by Charles F. Orvis of Vermont in 1874. Orvis first introduced the idea of using light metals with multiple perforated holes to construct the housing, resulting in a lighter reel that also allowed the spooled fly line to dry more quickly than a conventional, solid-sided design. Early fly reels placed the crank handle on the right side of the reel. Most had no drag mechanism, but were fitted with a click/pawl mechanism intended to keep the reel from overrunning when line was pulled from the spool. To slow a fish, the angler simply applied hand pressure to the rim of the revolving spool (known as "palming the rim"). Later, these click/pawl mechanisms were modified to provide a limited adjustable drag of sorts. Although adequate for smaller fish, these did not possess a wide adjustment range or the power to slow larger fish. | Fishing reel | Wikipedia | 485 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
At one time, multiplier fly reels were widely available. These reels had a geared line retrieve of 2:1 or 3:1 that allowed faster retrieval of the fly line. However, their additional weight, complexity and expense did not justify the advantage of faster line retrieval in the eyes of many anglers. As a result, today they are rarely used, and have largely been replaced by large-arbor designs with large diameter spools for faster line retrieval.
Automatic fly reels use a coiled spring mechanism that pulls the line into the reel with the flick of a lever. Automatic reels tend to be heavy for their size, and have limited line capacity. Automatic fly reels peaked in popularity during the 1960s, and since that time they have been outsold many times over by manual fly reels.
Modern fly reels typically have more sophisticated disc-type drag systems made of composite materials that feature increased adjustment range, consistency, and resistance to high temperatures from drag friction. Most of these fly reels also feature large-arbor spools designed to reduce line memory, maintain consistent drag and assist the quick retrieval of slack line in the event a hooked fish makes a sudden run towards the angler. Most modern fly reels are ambidextrous, allowing the angler to place the crank handle of the reel on either the right or the left side as desired.
Saltwater fly reels are designed specifically for use in an ocean environment. Saltwater fly reels are normally large-arbor designs, having a much larger diameter spool than most freshwater fly reels. These large arbor reels provide an improved retrieve ratio and considerably more line and backing capacity, optimizing the design for the long runs of powerful ocean game fish. To prevent corrosion, saltwater fly reels often use aerospace aluminum frames and spools, electroplated and/or stainless steel components, with sealed and waterproof bearing and drive mechanisms.
Fly reel operation
Fly reels are normally manual, single-action designs. Rotating a handle on the side of the reel rotates the spool which retrieves the line, usually at a 1:1 ratio (i.e., one complete revolution of the handle equals one revolution of the spool). Fly reels are one of the simplest reels and have far fewer parts than a spinning reel. The larger the fish the more important the reel becomes. On the outside of the reel there are two levels of knobs these are the spool release and the drag adjustment. | Fishing reel | Wikipedia | 511 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Fly reel drag systems
Fly-reel drag systems have two purposes. One, they prevent spool overrun when stripping line from the reel while casting, and two, to tire out running fish by exerting pressure on the line that runs in the opposite direction. There are four main drag systems that are used with the fly reel. These are the ratchet-and-pawl, caliper drags, disc drags, and center-line drags. The ratchet-and-pawl drag clicks automatically while the spool is spinning. The caliper drag causes the calipers to brush up against the reel spool. A disc drag is when pressure is applied on the plates which then applies pressure on the spool. Center-line drags also known as the best kind of drag because the pressure is directly on the spool close to the axis of rotation.
Sidecast reel
The sidecast reel takes elements of the design of the centrepin reel, but adds a bracket that allows the reel to be rotated 90° for casting and then returned to the original position to retrieve line. In the casting position, the spool face is perpendicular to the rod and the axle is parallel, and the line is free to slide off the side of the spool like on a spinning reel. The advantage of such design is that the reel is direct-driven, and during casting the line release is as smooth as that of a spinning reel, but it does require an extra hand movement to start reeling.
Sidecast reels are popular with anglers in Australia for all forms of freshwater and saltwater fishing. Most common is their use for surf fishing (beachcasting), or off the rocks, often with a larger diameter spool () and paired with a surfcasting rod. The most famous brand of sidecast reels is Alvey Reels, a Brisbane-based fishing tackle manufacturer established in 1920.
Conventional reel | Fishing reel | Wikipedia | 392 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
The conventional reel, also known as the trolling reel (due to its popularity in recreational boat trolling) or "drum reel" (due to its often drum-like cylindrical shape), is the most classical design of multiplier reels. It can be mounted (more often) above or below the rod handle, with the spool axis being perpendicular to the rod. In such a setup the line does not go over the end of the spool like it does with a spinning reel. Most modern conventional reels have a line guide that slides left and right when cranking to ensure a more even wrapping of the line onto the spool.
There are two types of trolling reels depending on the drag system design, namely the star drag reels and lever drag reels. Star drag reels are like most baitcasters, because they have a star-shaped drag control knob used to apply drag as well as a little lever to put them into free spool. The lever drag reel uses a drag lever to perform both functions as it can apply drag and put the reel into free spool. With either type, care must be taken to prevent backlash while they are in free spool. Keeping a thumb on the spool is one way to prevent a free spool backlash. Some smaller sizes of conventional reels can be cast, but large conventional reels are not meant for casting; the larger they are the more difficult they become to cast. Conventional reels are for really big fish and are usually used offshore. As a tool for Deep-sea fishing, they are mostly designed for trolling but can also be used for drift fishing, butterfly jigging and "deep drop" fishing. They are usually mounted on short, often very stiff rods called "boat" rods.
Baitcasting reel | Fishing reel | Wikipedia | 366 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
The baitcasting reel or baitcaster is a multiplying reel like modified from the conventional reel, but with a lighter spool and a higher, more forwardly positioned line guide to facilitate farther and smoother casting, hence the name. The baitcasting reel is always mounted above the rod handle (of what is known as a "casting rod"), hence its other name given to it in New Zealand and Australia, the overhead reel. The line is stored on a bearing-supported, more freely revolving spool that is geared so that a single revolution of the crank handle results in multiple (usually 4× or more) revolutions of the spool. The baitcasting reel design will operate well with a wide variety of fishing lines ranging from braided multifilament, heat-fused "Superlines", copolymer, fluorocarbon and nylon monofilaments (see Fishing line). Most baitcasting reels can also easily be palmed or thumbed to increase the drag, set the hook, or to accurately halt the lure at a given point in the cast.
The baitcasting reel dates from at least the mid-17th century, but came into wide use by amateur anglers during the 1870s. Early baitcasting reels were often constructed with brass or iron gears, with casings and spools made of brass, German silver or hard rubber. Featuring multiplying gears ranging from 2:1 to 4:1, these early reels had no drag mechanism, and anglers used their thumb on the spool to provide resistance to runs by a fish. As early as the 1870s, some models used bearings to mount the spool; as the free-spinning spool tended to cause backlash with strong pulls on the line, manufacturers soon incorporated a clicking pawl mechanism. This "clicker" mechanism was never intended as a drag, but used solely to keep the spool from overrunning, much like a fly reel. Baitcasting reel users soon discovered that the clicking noise of the pawls provided valuable audible warning that a fish had taken the live bait, allowing the rod and reel to be left in a rod holder while awaiting a strike by a fish. | Fishing reel | Wikipedia | 450 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Most fishing reels are suspended from the bottom side of the rod, since this position doesn't require wrist strength to overcome gravity while enabling the angler to cast and retrieve without changing hands. The baitcasting reel's unusual mounting position atop the rod is an accident of history. Baitcasting reels were originally designed to be cast when positioned atop the rod, then rotated upside-down to operate the crank handle while playing a fish or retrieving line. However, in practice most anglers preferred to keep the reel atop the rod for both cast and retrieve by simply transferring the rod to the left hand for the retrieve, then reverse-winding the crank handle. Because of this preference, mounting the crank handle on the right side of a bait casting reel (with standard clockwise crank handle rotation) has become customary, though models with left-hand retrieve have gained in popularity in recent years thanks to user familiarity with the spinning reel.
Many of today's baitcasting reels are constructed using aluminium alloy, stainless steel, synthetic composites such as fiberglass-reinforced plastic or carbon fiber, alone or in combination; newer but more expensive materials such as titanium and magnesium alloys can also be found occasionally. They call for a rod that has a trigger finger hook located in the handle area. They typically include a level-wind mechanism to prevent the line from being trapped under itself on the spool during rewind and interfering with subsequent casts. Many are also fitted with anti-reverse handles and drags designed to slow runs by large and powerful game fish. Because the baitcasting reel uses the weight and momentum of the lure to pull the line from the rotating spool, it normally requires lures weighing 1/4 oz. or more to cast a significant distance. Recent developments have seen baitcasting reels with gear ratios as high as 7.1/1. Higher gear ratios allow much faster retrieval of line, but sacrifice some amount of strength in exchange, since the additional gear teeth required reduces torque as well as the strength of the gear train. This could be a factor when fighting a large and powerful fish. | Fishing reel | Wikipedia | 428 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Two variations of the revolving spool bait casting reel are the conventional surf fishing reel and the big game reel. These are very large and robust fishing reels, designed and built for heavy saltwater species such as tuna, marlin, sailfish and sharks. Surf fishing reels are normally mounted to long, two-handed rods; these reels frequently omit level-wind and braking mechanisms to achieve extremely long casting distances. Big game reels are not designed for casting, but are instead used for trolling or fishing set baits and lures; they are ideal for fighting large and heavy fish off a pier or boat. These reels normally use sophisticated star or lever drags to play out huge saltwater gamefish.
Baitcasting Reel Operation
To cast a baitcasting rod and reel, the reel is turned on its side, the "free spool" feature engaged, and the thumb placed on the spool to hold the lure in position. The cast is performed by snapping the rod backward to the 2 o'clock position, then casting it forward in a smooth motion, allowing the lure to pull the line from the reel. The thumb is used to contact the line, moderating the revolutions of the spool and braking the lure when it reaches the desired aiming point. Though modern centrifugal and/or magnetic braking systems help to control backlash, using a bait casting reel still requires practice and a certain amount of finesse on the part of the fisherman for best results.
Advantages of Baitcasting Reels
While spincasting and spinning reels are easier to operate because fishing line leaves the spool freely during a cast, baitcasting reels have the potential to overrun: a casting issue in which the reel's spool does not spin at a rate equal to the speed of fishing line leaving the reel. Professional fishermen, however, prefer baitcasters because baitcasting reels allow anglers more control over their casts. Since a baitcaster's spool spins along with the fishing line leaving the reel, a simple flick of the thumb can stop a cast early or slow a lure while it is still in the air. This grants anglers such as bass fishermen more accuracy in their casts. Furthermore, a baitcaster's design allows a fisherman to make casts at a faster rate, even with heavier baits. | Fishing reel | Wikipedia | 476 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Disadvantages Of Baitcasting Reels
Effective use of baitcasting reels requires prior experience and a developed skill set, thus it is unsuitable for beginners.
There are higher risks of getting backlashes during the cast without proper techniques.
One must know about spool tension adjustment for different spool sizes.
Unsuitable for light lures.
More costly than spinning reels.
Fixed-spool
Fixed spool reels can have either an "open" design, where the spool is exposed to the outside; or an "enclosed" design, where the spool is concealed under an enclosure with a front hole that allows passage of the line. There is typically an internal axle that imparts a slight reciprocating motion to the spool, which allows the line to be wrapped in a more evenly distributed fashion.
Spinning reel
Spinning reels, also called fixed spool reels or "egg beaters", are open-design fixed-spool reels that were in use in North America as early as the 1870s. They were originally developed to allow the use of artificial flies, or other lures for trout or salmon, that were too light in weight to be easily cast by conventional or baitcasting reels. Spinning reels are normally mounted below the rod; this positioning conforms to gravity, requiring no wrist strength to maintain the reel in position. For right-handed persons, the spinning rod is held and cast by the strong right hand, leaving the left hand free to operate the crank handle mounted on the left side of the reel. Invention of the spinning reel solved the problem of backlash, since the reel had no rotating spool capable of overrunning and tangling the line. | Fishing reel | Wikipedia | 343 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
The name of Holden Illingworth, a textiles magnate, was first associated with the modern form of fixed-spool spinning reel. When casting the Illingworth reel, line was drawn off the leading edge of the spool, but was restrained and rewound by a line pickup, a device which orbits around the stationary spool. Because the line did not have to pull against a rotating spool, much lighter lures could be cast than with conventional reels.
In 1948, the Mitchell Reel Company of Cluses, France introduced the Mitchell 300, a spinning reel with a design that oriented the face of the fixed spool forward in a permanently fixed position below the fishing rod. The Mitchell reel was soon offered in a range of sizes for all fresh and saltwater fishing. A manual line pickup was used to retrieve the cast line, which eventually developed into a wire bail design that automatically recaptured the line upon cranking the retrieve handle. An anti-reverse lever prevented the crank handle from rotating while a fish was pulling line from the spool, and this pull can be altered with adjustable drag systems which allow the spool to rotate, but not the handle. With the use of light lines testing from two to six pounds, modern postwar spinning reels were capable of casting lures as light as , and sometimes lighter.
With all fixed-spool reels, the line is released in coils or loops from the leading edge of the non-rotating spool. To shorten or stop the outward cast of a lure or bait, the angler uses a finger or thumb placed in contact with the line and/or the leading edge of the spool to retard or stop the flight of the lure. Because of the design's tendency to twist and untwist the line as it is cast and retrieved, most spinning reels operate best with fairly limp and flexible fishing lines. | Fishing reel | Wikipedia | 384 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Though spinning reels do not suffer from backlash, line can occasionally be trapped underneath itself on the spool or even detach from the reel in loose loops of line. Some of these issues can be traced to overfilling the spool with line, while others are due to the way in which the line is wound onto the spool by the rotating bail or pickup. Various oscillating spool mechanisms have been introduced over the years in an effort to solve this problem. Spinning reels also tend to have more issues with twisting of the fishing line. Line twist in spinning reels can occur from the spin of an attached lure, the action of the wire bail against the line when engaged by the crank handle, or even retrieval of line that is under load (spinning reel users normally pump the rod up and down, then retrieve the slack line to avoid line twist and stress on internal components). To minimize line twist, many anglers who use a spinning reel manually reposition the bail after each cast with the pickup nearest the rod to minimize line twist.
Fixed spool reel operation
Fixed spool reels are cast by grasping the line with the forefinger against the rod handle, opening the bale arm and then using a backward swing of the rod followed by a forward cast while releasing the line with the forefinger. The point of release should be trialled to find optimum angle for your casting. The forefinger is then placed in contact with the departing line and the leading edge of the spool to slow or stop the outward cast. On the retrieve, one hand operates the crank handle, while the large rotating wire cage or bail (either manually or trigger-operated) serves as the line pickup, restoring the line to its original position on the spool.
Fixed spool advantages
Spinning reels were originally developed to better cast light-weight lures and baits. Today, spinning reels continue to be an excellent alternative to baitcasters, reels which have difficulty casting lighter lures. Furthermore, because spinning reels do not suffer from backlash, spinning reels are easier and more convenient to use for some fishermen.
Spincast reel | Fishing reel | Wikipedia | 434 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Spincast reels are fixed-spool reels with the spool and line pickup mechanisms enclosed within a cylindrical or cylindroconoidal cover, which has a hole at the front to transmit the line. The first commercial spincast reels were introduced by the Denison-Johnson Reel Company and the Zero Hour Bomb Company (ZEBCO) in 1949. Spincast reels avoid the problem of backlash found in baitcast designs, while reducing line twist and snare complaints sometimes encountered with traditional spinning reel designs. Just as with the spinning reel, the line is thrown from a fixed spool and can therefore be used with relatively light lures and baits. However, the spincast reel eliminates the large wire bail and line roller of the spinning reel in favor of one or two simple pickup pins and a metal cup to wind the line on the spool. Traditionally mounted above the rod, the spincast reel is also fitted with an external nose cone that encloses and protects the fixed spool. Spincast reels may also be described as closed face reels.
With a fixed spool, spincast reels can cast lighter lures than bait cast reels, although friction of the nose cone guide and spool cup against the uncoiling line reduces casting distance compared to spinning reels. Spincast reel design requires the use of narrow spools with less line capacity than either baitcasting or spinning reels of equivalent size, and cannot be made significantly larger in diameter without making the reel too tall and unwieldy. These limitations severely restrict the use of spin cast reels in situations such as fishing at depth, when casting long distances, or where fish can be expected to make long runs. Like other types of reels, spin cast reels are frequently fitted with both anti-reverse mechanisms and friction drags, and some also have level-wind (oscillating spool) mechanisms. Most spin cast reels operate best with limp monofilament lines, though at least one spin cast reel manufacturer installs a thermally fused "superline" into one of its models as standard equipment. During the 1950s and into the mid-1960s, they were widely used and very popular, though the spinning reel has since eclipsed them in popularity in North America. They remain a favorite fishing tool for catfish fishing and also for young beginners in general. | Fishing reel | Wikipedia | 486 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Spincast reel Operation
Pressing a button on the rear of the reel disengages the line pickup, and the button is then released during the forward cast to allow the line to fly off the spool. The button is pressed again to stop the lure at the position desired. Upon cranking the handle, the pickup pin immediately re-engages the line and spools it onto the reel.
Underspin reel
Underspin reels or triggerspin reels are variants of spincast reels that is designed for mounting underneath a standard spinning rod. The reel foot is now located on top of the reel (like a spinning reel), and the line release button is replaced by a front lever. With the reel's weight suspended beneath the rod, underspin reels are generally more comfortable to cast and hold for long periods, and the ability to use all standard spinning rods greatly increases its versatility compared to traditional spin cast reels.
Underspin Reel Operation
When the line release lever/trigger is lifted up by the forefinger (usually the index finger of the rod-holding hand), the line catch inside the reel disengages and retracts, and the line is free to slide off the fixed spool. In some modern designs (e.g. the Pflueger "President" reel), keeping the lever fully pulled up will however protrude the whole spool forward and pinch the line against the enclosure interior, thus halting the line release. During line retrieval, the mechanism inside the reel will engage the line catch again, which protrudes out to "grab" the line and wrap it around the spool. When necessary, the lever can be activated once again to stop the lure at a given point in the retrieval.
Mechanisms
Reel mechanisms
Direct-drive reel
Direct-drive reels have the spool and handle directly coupled. When the angler is reeling in a fish, there's user operation, but when the line is going out, and the fish is taking the bait and the reel handles are visible moving likewise to the line unwinding. With a fast-running fish, this may have consequences for the angler's knuckles. Traditional fly reels are direct-drive. | Fishing reel | Wikipedia | 456 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Anti-reverse reel
In anti-reverse reels, a mechanism allows line to pay out while the handle remains stationary. Depending on the drag setting, line may also pay out, as with a running fish, while the angler reels in. Baitcasting reels and many modern saltwater fly reels are examples of this design.
The mechanism works either with a 'dog' or 'pawl' design that engages into a cog wheel attached to the handle shaft. The latest design is Instant Anti-Reverse, or IAR. This system incorporates a one-way clutch bearing or centrifugal force fly wheel on the handle shaft to restrict handle movement to forward motion only.
Drag mechanisms
Drag systems are a mechanical means of applying variable pressure to the line spool or drive mechanism to act as a friction brake against outgoing spool rotation. Under normal load, the friction holds the spool and the gears in synchrony, allowing the user to reel in the line; if the tension along the fishing line exceeds the drag setting, the braking friction is overcome and the spool will reverse-rotate with resistance until the line tension drops back below the drag setting. Some designs also have an internal spring clicker that generates warning noises to remind the user whenever the line tension exceeds the drag setting. Such mechanism serves to cap off the maximum line tension and prevents it from overloading and breaking when landing a strong or vigorously fighting fish. In combination with rod flexing and adequate angling techniques, the angler can catch fish much larger than the on-paper breaking strength of the line by "walking" and gradually tiring out the fish. | Fishing reel | Wikipedia | 332 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
The mechanics of drag systems usually consist of a number of frictional discs (drag washers) arranged in a coaxial stack on the spool shaft, or in some cases, on the drive shaft. There is generally a screw or lever mechanism that presses perpendicularly against the washers, which creates friction especially when each washer slides against adjacent ones – the higher the pressure, the greater the resistance. Drag washers are commonly made of materials such as felt, Teflon, carbon fiber or other reinforced plastics, and usually have metallic (usually steel) washers stacked intermittently to help distribute shear stress more evenly. Since large fish can generate a lot of pulling power, reels with higher available drag forces for higher-test lines will generate greater heat, and therefore use stronger and more heat-resistant materials, often with coated with specialty oil or grease to prevent burning and unwanted locking between adjacent washers. A good drag system one that is durable and generates precise, consistent and smooth (with no jerkiness) resistance.
Spinning reels
Spinning reels have two types of drag design: front or rear. All spinning reels come with front drag, but rear drag, also called "bait runner" or "baitfeeder", is an additional feature.
Front drags are basically a screw knob mounted to the front end of the spool, which exerts direct graduated axial pressure on the drag washers on the main pinion. To adjust these, the user needs to reach around the front to turn and tighten/loosen the spool. Front drags are mechanically simpler and usually more consistent in performance and capable of higher drag forces.
Rear drags, on the other hand, have an adjustment screw on the back of the reel along with a separate lever to activate its use. It automatically flips off whenever the fisherman touches the spool-crank and the front drag then steps in at that moment and incorporates its setting into the fight. Manufacturers seldom issue over ten pounds of drag from the rear but are said to be more complicated mechanically and usually not as precise or smooth as front drags since the drag itself is often part of the drive shaft and not the spool. They are for the first moments of the encounter when the fish has the bait in its mouth and is running with it without the hook set yet. The rear drag stops when the fisherman turns his spool-crank to engage the culprit on the run, and sets the hook. | Fishing reel | Wikipedia | 499 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Casting reels
Conventional overhead, trolling or baitcasting type reels usually use one of two types of drags: star or lever. The most common and simplest mechanically is the so-called 'star drag' because the adjustor wheel looks like a star with rounded points. Star drags work by screw action to increase or decrease the pressure on the washer stack which is usually located on the main driving gear. Reels with star drags generally have a separate lever which allows the reel to go into "freespool" by disengaging the spool from the drive train completely and allowing it to spin freely with little resistance. The freespool position is used for casting, letting line out and/or allowing live bait to move freely.
Lever drags work through cam action to increase or decrease pressure on the drag washers located on the spool itself. Most lever drags offer preset drag positions for strike (reduced drag to avoid tearing the hook out of the fish), full (used once the hook is set) and freespool (see above). Lever drags are simpler and faster to adjust during the fight. And, since they use the spool for the washer stack rather than the drive gear, the washers can be larger, offering more resistance and smoother action. The disadvantage is that in freespool, there can be residual and unwanted resistance since the drag mechanism may not be completely out of the picture without resorting to more complex mechanics.
Setting the drag
Proper drag setting depends on fishing conditions, line test (break strength) and the size and type of fish being targeted. Often it is a matter of "feel" and knowing the setup to get the drag right. | Fishing reel | Wikipedia | 350 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
With spinning reels, closed-face reels and conventional reels with star drags, a good starting point is to set the drag to about one-third to one-half the breaking strength of the line. For example, if the line is rated at test, a drag setting that requires of force on the line to move the spool would be appropriate. This is only a rule of thumb. For lever drag reels with a strike position, most anglers start by setting the drag at the strike position to one-third the break strength of the line. This usually allows the full position to still be safely under the line rating while providing flexibility during the fight. Depending on the conditions, some anglers may leave their reels in freespool then setting the anti-reverse or engaging the drag on hookup.
Braking mechanisms
When casting, the terminal tackles flying through the air will decelerate due to air resistance, causing the line release out of the reel (which is mainly driven by the forward momentum of the terminal tackles) to slow down exponentially. This is particularly apparent when casting lightweight and/or poorly aerodynamic baits/lures, or when casting against the wind. If the angler is using a multiplier reel, its rotary spool often still has sufficient rotational momentum to keep itself spinning with a far more gradual deceleration. This deceleration mismatch between the line release and the spool rotation causes the lagging line to inertially "float" off the spool in loose loops before it can exit the reel. Some of these floating loops eventually get large enough to be pulled into the narrow spaces between the spool and the reel chassis – a phenomenon known as a spool overrun or a backlash, which often snares the loops into a very messy tangle (colloquially called a "bird's nest" or "birdie") that is notoriously difficult to untangle. Such backlashing is unique to multiplier reels, particularly baitcasters, and is not present with fixed-spool reels such as a spinning reel. | Fishing reel | Wikipedia | 427 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
To deal with backlashing, most modern baitcasting reels have a so-called "cast control" that serves to reduce the incidence of spool overrun at the cost of sacrificing casting distances. Each time a different lure weight is attached, the cast control must be adjusted to calibrate for the difference in lure momentum and deceleration. The users are also required to learn the skill of "feathering the spool" with their thumb to apply direct tactile friction on the spool surface to slow down or even stop it from spinning.
Spool tension
Spool tension is an adjustable screw knob that is coaxial to the reel spool. When tightened, the knob exerts axial pressure on the spool gear and generates a consistent frictional resistance when the spool is free-spinning.
Centrifugal braking
Centrifugal braking uses a series of spring-loaded "blocks" on the spool, which can move radially outwards under centrifugal force when the spool is spinning rapidly. These blocks each have a rubber piece that can rub against the reel chassis, creating additional friction that slows down the spool until the blocks retract back under spring tension. Some reels, such as the Shimano SVS Infinity, have designs that allow each centrifugal blocks to be locked and temporarily disabled.
Magnetic braking
Magnetic braking incorporates the principles of Lenz's law to create a contactless resistance to the spool spinning. The reel chassis (usually on the side opposite to the crank handle) has a circularly arranged array of magnets creating a magnetic field. When the spool rotates, the metallic frame cuts through the field lines and experiences an electromagnetic resistance, which changes with the spool speed but persists as long as the spool is still moving.
Electronic braking
Electronic braking uses an electronic circuit to monitor the speed of spool rotation and apply pre-calculated resistance via an internal actuator. The most famous is the Shimano Curado DC ("Digital Control") series, first introduced in 2003 and having remained the only electronically braked fishing reel in the world for two decades until early 2023, when two similar products, the Daiwa IMZ Limitbreaker and the KastKing iReel IFC ("Intelligent Frequency Control"), were announced respectively. | Fishing reel | Wikipedia | 483 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Line guide mechanisms
Line guides are unique to multiplier reels, as more evenly wound lines on the spool would allow the reel to function more smoothly and prevent unwanted "overspill" of line at either end of the spool. The vast majority of line guides are a simple ring or short cylinder with a internal diameter, which slides horizontally along a spiral-groove shaft. The side-to-side motion of the line guide continuously pushes and realigns the line onto different section of the spool, thus allowing a more even distribution of winding.
While line guides are crucial to reel operation during retrieval, during casting it becomes more of a hindrance because the line will have to go through its narrow internal channel to leave the reel. This creates additional drag from friction (especially when the line kinks against the back rim of the guide) or when loose line loops whips against the line guide. This exacerbates backlashing as the narrow line guide channel often limits how fast the line can leave the reel, and is particularly a problem when the line guide stops near the side of the reel when the reel gears are disengaged during casting. There are design modifications on line guides aimed to minimize resistance against line release, most of which involve having a conical or funnel-shaped line guide that reduce the kinking angle between the line and the guide frame, which only partially resolves the drag issue. Another less-successful modification involves having an open-and-shut "gate" as a line guide, which unfortunately can catch and trap the line between the gaps of the shutter.
In 2011, the famous Japanese fishing tackle brand Daiwa introduced its famous TWS (T-Wing System) design, which have a T-shaped/inverted trianguloid line guide that has a broad top section that presents a much wider channel for line exit, while during retrieval the top bar tilts back and down to push the line into the much narrower bottom section. The TWS has become a celebrated success for Daiwa, and remained a patented trademark that was largely unchallenged for years. | Fishing reel | Wikipedia | 425 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
Another notable 21st century line guide design, patented by the Shenzhen/New York City-based Chinese-American brand KastKing in 2023, is named the "Axis Eye" or "willowleaf guide". It has a silicon nitride-coated, rounded rectangle frame with a slightly serpentine shaped top profile, which can horizontally rotate 90° to alternate between a wide and a narrow cross-sectional width. During casting, the line guide is rotated to a transverse orientation, which presents a -wide line channel, allowing the line to exit with minimal drag; during retrieval, the line guide is rotated to a longitudinal orientation, which narrows the line channel down to less than 3 mm.
Notable brands
Japan
Shimano
Daiwa
United States
Pure Fishing
ABU Garcia
Penn Reels
Pflueger
Shakespeare Fishing Tackle
Orvis
Scientific Anglers
Australia
Alvey Reels | Fishing reel | Wikipedia | 174 | 47338 | https://en.wikipedia.org/wiki/Fishing%20reel | Technology | Hunting and fishing | null |
A fishing line is any flexible, high-tensile cord used in angling to tether and pull in fish, in conjunction with at least one hook. Fishing lines are usually pulled by and stored in a reel, but can also be retrieved by hand, with a fixed attachment to the end of a rod, or via a motorized trolling outrigger.
Fishing lines generally resemble a long, ultra-thin rope, with important attributes including length, thickness, material and build. Other factors relevant to certain fishing practice include breaking strength, knot strength, UV resistance, castability, limpness, stretch, memory, abrasion resistance and visibility. Traditional fishing lines are made of silk, while most modern lines are made from synthetic polymers such as nylon, polyethylene or polyvinylidene fluoride ("fluorocarbon") and may come in monofilament or braided (multifilament) forms.
Terminology
Fishing with a hook-and-line setup is called angling. Fish are caught when one are drawn by the bait/lure dressed on the hook into swallowing it in whole, causing in the hook (usually barbed) piercing the soft tissues and anchoring into the mouthparts, gullet or gill, resulting in the fish becoming firmly tethered to the line. Another more primitive method is to use a straight gorge, which is buried longitudinally in the bait such that it would be swallowed end first, and the tension along the line would fix it cross-wise in the fish's stomach or gullet and so the capture would be assured. Once the fish is hooked, the line can then pull it towards the angler and eventually fetch it out of the water (known as "landing" the fish). Heavier fish can be difficult to retrieve by only dragging the line (as it might overwhelm and snap the line) and might need to be landed via additionally using a hand net (a.k.a. landing net) or a hooked pole called a gaff. | Fishing line | Wikipedia | 412 | 47339 | https://en.wikipedia.org/wiki/Fishing%20line | Technology | Hunting and fishing | null |
Trolling is a technique where one or more lines, each with at least one hooked fishing lure at the end, is dragged through the water, which mimick schooling forage fish. Trolling from a moving boat is used in both big-game and commercial fishing as a method of catching large open-water species such as tuna and marlin (which are instinctively drawn to schoolers), and can also be used when angling in freshwater as a way to catch salmon, northern pike, muskellunge and walleye. The technique allows anglers to cover a large body of water in a short time without having to cast and retrieve lures constantly.
Longline fishing and trotlining are commercial fishing technique that uses many secondary lines with baited hooks hanging perpendicularly from a single main line.
Snagging is a fishing technique where a large, sharp grappling hook is used to pierce the fish externally in the body instead of inside the fish's mouth, and is therefore not the same as angling. Generally, a large open-gaped treble hook with a heavy sinker is cast into a river containing a large amount of fish (such as salmon) and is quickly jerked and reeled in, which gives the snag hook a gaff-like "clawing" motion that can spear its sharp points past the scales and skin and deep into the body. Modern technologies such as underwater cameras are sometimes used to help improve the timing of snagging. Due to the mutilating nature of this technique (where the fish are typically too deeply injured to be released alive), snagging is frequently deemed an unethical and illegal method, and some snagging practitioners have added procedures to disguise the snagging practice, such as adding baits or jerking the line using a fishing rod, to make it look like angling.
Sections
Traditionally, only a single thread of line is used to connect the hook with the rod and reel. However, most modern angling setups use at least two sections of line (typically the mainline and the leader) joined with a bend knot (such as the famously named fisherman's knot). Occasionally a swivel might be used to join the lines and reduce the bait/lure spinning due to the inherent line twisting from a fixed-spool reel. | Fishing line | Wikipedia | 473 | 47339 | https://en.wikipedia.org/wiki/Fishing%20line | Technology | Hunting and fishing | null |
A typical modern angling setup can include the following line sections:
Backing is the rearmost section of the fishing line and typically used only to "pad up" the spool of the fishing reel, in order to prevent unwanted slippage between the mainline and the (usually metallic and well polished) spool surface, increase the effective radius of the spooled line and hence the retrieval speed (i.e. inches per turn), and to shorten the "jump" distance during line release in spinning reels. The backing can also act as a line reserve in case a powerful fish that manages to overpower the drag mechanism of the reel and stretch out the entire length of the mainline.
Mainline is the main section of the fishing line, and the portion that primarily interacts with the rod, line guides and reel. This is the section that handles most of the tensile stress when retrieving the line.
Leader is the frontmost section of the fishing line that is attached to the hook/lure, and the portion that most likely will be in actual physical contact with the fish. Many larger, feistier target fish warrants a strong mainline, which might make it too thick to thread through the eye of the hook, thus necessitating a thinner line to "lead" into the hook (hence the name). Leader lines usually use high-specific strength material with clear colors and water-like refractive indices (thus harder for the fish to spot it) such as polyvinylidene fluoride (PVDF, commonly called "fluorocarbon"), or even stainless steel/titanium wires to reduce breakage due to abrasion damage or fish biting. The leader line can also serve as a sacrificial device, as having a leader rated at a designated breaking strength less than that of the rod and mainline helps to cap the transferred stress and protect those more costly gears/tackles from overloading and breaking (similar to how a fuse protects a circuitry), which will minimize loss and cost of repairs/replacements if the fish manages to overpower the angler's gear setup.
Tippet or trace is used occasionally in fly fishing, and serves as a secondary leader that thread to the much smaller and delicate fly hooks.
History | Fishing line | Wikipedia | 459 | 47339 | https://en.wikipedia.org/wiki/Fishing%20line | Technology | Hunting and fishing | null |
Early lines
Leonard Mascall, in his book from 1596 titled "A Booke of fishing with Hooke and Line, and of all other instruments thereunto belonging". followed in many ways after Dame Juliana Berners, has an excerpt establishing silk worms in the area of England at that time:
... ...
And another excerpt explaining compiling a silk leader-line for a catgut fly-line.
So back then there was silk and horse hair used for angling.
As written in 1667 by Samuel Pepys, the fishing lines in his time were made from catgut. Later, silk fishing lines were used around 1724.
Modern lines
Modern fishing lines intended for spinning, spin cast, or bait casting reels are almost entirely made from artificial substances, including nylon (typically 610 or 612), polyvinylidene fluoride (PVDF, also called fluorocarbon), polyethylene, Dacron and UHMWPE (Honeywell's Spectra or Dyneema). The most common type is monofilament, made of a single strand. Fishermen often use monofilament because of its buoyant characteristics and its ability to stretch under load. The line stretch has advantages, such as damping the force when setting the hook and when fighting strong fish. On very far distances the damping may become a disadvantage. Recently, other alternatives to standard nylon monofilament lines have been introduced made of copolymers or fluorocarbon, or a combination of the two materials. Fluorocarbon fishing line is made of the fluoropolymer PVDF and it is valued for its refractive index, which is similar to that of water, making it less visible to fish. Fluorocarbon is also a denser material, and therefore, is not nearly as buoyant as monofilament. Anglers often utilize fluorocarbon when they need their baits to stay closer to the bottom without the use of heavy sinkers. There are also braided fishing lines, cofilament and thermally fused lines, also known as "superlines" for their small diameter, lack of stretch, and great strength relative to standard nylon monofilament lines. Braided, thermally fused, and chemically fused varieties of "superlines" are now readily available. | Fishing line | Wikipedia | 479 | 47339 | https://en.wikipedia.org/wiki/Fishing%20line | Technology | Hunting and fishing | null |
Specialty lines
Fly lines consist of a tough braided or monofilament core, wrapped in a thick waterproof plastic sheath, often of polyvinyl chloride (PVC). In the case of floating fly lines, the PVC sheath is usually embedded with many "microballoons", or air bubbles, and may also be impregnated with silicone or other lubricants to give buoyancy and reduce wear. In order to fill up the reel spool and ensure an adequate reserve in case of a run by a powerful fish, fly lines are usually attached to a secondary line at the butt section, called backing. Fly line backing is usually composed of braided dacron or gelspun monofilaments. All fly lines are equipped with a leader of monofilament or fluorocarbon fishing line, usually (but not always) tapered in diameter, and referred to by the "X-size" (0X, 2X, 4X, etc.) of its final tip section, or tippet. Tippet size is usually between 0X and 8X, where 0X is the thickest diameter, and 8X is the thinnest. There are exceptions to this, and tippet sizes do exist outside of the 0X–8X parameter.
Tenkara lines are special lines used for the fixed-line fishing method of tenkara. Traditionally these are furled lines the same length as the tenkara rod. Although original to Japan, these lines are similar to the British tradition of furled leader. They consist of several strands being twisted together in decreasing numbers toward the tip of the line, thus creating a taper that allows the line to cast the fly. It serves the same purpose as the fly-line, to propel a fly forward. They may be tied of various materials, but most commonly are made of monofilament.
Wire lines are frequently used as leaders to prevent the fishing line from being severed by toothy fish. Usually braided from several metal strands, wire lines may be made of stainless steel, titanium, or a combination of metal alloys coated with plastic. | Fishing line | Wikipedia | 437 | 47339 | https://en.wikipedia.org/wiki/Fishing%20line | Technology | Hunting and fishing | null |
Stainless-steel line leaders provide:
bite protection – it is extremely hard for fish to cut the steel wire, regardless of jaw and teeth strength and sharpness,
abrasion resistance – sharp rocks and objects can damage other lines, while steel wire can cut through most of the materials,
single-wire (single-strand) leaders are not as flexible as multi-strand steel wire, but are extremely strong and tough,
multi-strand steel wire leaders are very flexible, but are somewhat more abrasive and more damage-prone than single-strand wires.
Titanium fishing leaders are actually titanium–nickel alloys that have several very important features:
titanium leader lines are very flexible, regardless of whether they are single- or multi-strand lines/wires,
these lines are very elastic – they can stretch up to 10% without permanent damage to the line itself – perfect for hook setting,
these lines are knottable just as nylon monofilament lines,
surface is rather hard and abrasion-resistant – great for fishing toothy fish,
titanium wire is corrosion-resistant and can last for a long time, even surpassing stainless-steel wires,
due to the strength and elasticity, titanium wires are almost entirely kink-proof.
Copper, monel and lead-core fishing lines are used as heavy trolling main lines, usually followed with fluorocarbon line near the lure or bait with fishing swivel between the lines. Due to their high density, these fishing lines sink rapidly in water and require less line for achieving desired trolling depth. On the other hand, these lines are relatively thick for desired strength, especially when compared with braided fishing lines and often require reels with larger spools.
Environmental impact
Discarded monofilament fishing line takes up to 600 years to decompose. There have been several types of biodegradable fishing lines developed to minimize the impact on the environment. | Fishing line | Wikipedia | 384 | 47339 | https://en.wikipedia.org/wiki/Fishing%20line | Technology | Hunting and fishing | null |
Hake is the common name for fish in the Merlucciidae family of the northern and southern oceans and the Phycidae family of the northern oceans. Hake is a commercially important fish in the same taxonomic order, Gadiformes, as cod and haddock.
Description
Hakes are medium-to-large fish averaging from in weight, with specimens as large as . The fish can grow up to in length with a lifespan of as long as 14 years.
Hake may be found in the Atlantic Ocean and Pacific Ocean in waters from deep. The fish stay in deep water during the day and come to shallower depths during the night. An undiscerning predator, hake feed on prey found near or on the bottom of the sea. Male and female hake are very similar in appearance.
After spawning, the hake eggs float on the surface of the sea where the larvae develop. After a certain period of time, the baby hake then migrate to the bottom of the sea, preferring depths of less than .
Merlucciidae
A total of 13 hake species are known in the family Merlucciidae:
Argentine hake (Merluccius hubbsi), found off Argentina
Benguela hake (Merluccius polli), found off South Africa
Deep-water hake (Merluccius paradoxus) found in the southern Atlantic Ocean
European hake (Merluccius merluccius), found off the Atlantic coast of Europe and western North Africa, in the Mediterranean Sea, and in the Black Sea
Gayi hake (Merluccius gayi), found in the North Pacific Ocean
North Pacific hake (Merluccius productus), found in the North Pacific
Offshore hake (Merluccius albidus), found off the United States
Panama hake (Merluccius angustimanus), found in the Eastern Pacific
Senegalese hake (Merluccius senegalensis), found off the Atlantic coast of western North Africa
Shallow-water hake (Merluccius capensis), found in the southern Atlantic Ocean
Silver hake (Merluccius bilinearis), found in the Northwest Atlantic Ocean
Southern hake (Merluccius australis), found off Chile and off New Zealand
Commercial use | Hake | Wikipedia | 477 | 47357 | https://en.wikipedia.org/wiki/Hake | Biology and health sciences | Acanthomorpha | Animals |
Not all hake species are viewed as commercially important, but the deep-water and shallow-water hakes are known to grow rapidly and make up the majority of harvested species. Indicators of quality in hake products for human consumption include white flesh free of signs of browning, dryness, or grayness, and with a fresh, seawater smell. Hake is sold as frozen, fillets or steaks, fresh, smoked, or salted.
Fisheries
The main catching method of deep-water hake is primarily trawling, and shallow-water hake is mostly caught by inshore trawl and longlining. Hake are mostly found in the Southwest Atlantic (Argentina and Uruguay), Southeast Pacific (Chile and Peru), Southeast Atlantic (Namibia and South Africa), Southwest Pacific (New Zealand), and Mediterranean and Black Sea (Italy, Portugal, Spain, Greece and France).
Over-exploitation
Due to over-fishing, Argentine hake catches have declined drastically. About 80% of adult hake has apparently disappeared from Argentine waters. Argentine hake is not expected to disappear, but the stock may be so low that it is no longer economical for commercial fishing. In addition, this adversely affects Argentine employment, because of many jobs in the fishing industries. Conversely, Argentine hake prices rose due to hake scarcity, reducing exports and affecting the economy.
In Chile, seafood exports, especially Chilean hake, have decreased dramatically. Hake export has decreased by almost 19 percent. The main cause of this decline is the February 2010 Chile earthquake and tsunami. These disasters destroyed most processing plants, especially manufacturing companies that produce fish meal and frozen fillets.
European hake catches are well below historical levels because of hake depletion in the Mediterranean and Black Sea. Various factors might have caused this decline, including a too-high Total Annual Catch, unsustainable fishing, ecological problems, juvenile catches, or non-registered catches.
Namibia is the only country that has increased its hake quota, from in 2009 to in 2010. Furthermore, the Namibian Ministry of Fisheries adheres to strict rules regarding the catch of hake. For example, the closed seasons for hake lasts approximately two months, in September and October, depending on the level of stock. This rule has been applied to ensure the regrowth of the hake population. Supplemental restrictions forbid trawling for Hake in waters less than deep (to avoid damaging non-target species habitat) and to minimize by-catch. | Hake | Wikipedia | 512 | 47357 | https://en.wikipedia.org/wiki/Hake | Biology and health sciences | Acanthomorpha | Animals |
Human introduction to non-native areas
Frank Forrester's Fishermens' Guide in 1885 mentions a hake that was transplanted from the coast of Ireland to Cape Cod on the coast of Massachusetts in the United States. It is uncertain which species it was, but the Fishermens' Guide stated:This is an Irish salt water fish, similar in appearance to the tom cod. In Galway bay, and other sea inlets of Ireland, the hake is exceedingly abundant, and is taken in great numbers. It is also found in England and France. Since the Irish immigration to America, the hake has followed in the wake of their masters, as it is now found in New York bay, in the waters around Boston, and off Cape Cod. Here it is called the stock fish, and the Bostonians call them poor Johns. It is a singular fact that until within a few years this fish was never seen in America. It does not grow as large here as in Europe, though here they are from ten to eighteen inches [250 to 460 mm] in length.... The general color of this fish is a reddish brown, with some golden tints—the sides being of a pink silvery luster. | Hake | Wikipedia | 247 | 47357 | https://en.wikipedia.org/wiki/Hake | Biology and health sciences | Acanthomorpha | Animals |
Titan is the largest moon of Saturn and the second-largest in the Solar System. It is the only moon known to have an atmosphere denser than the Earth's and is the only known object in space—other than Earth—on which there is clear evidence that stable bodies of liquid exist. Titan is one of seven gravitationally rounded moons of Saturn and the second-most distant among them. Frequently described as a planet-like moon, Titan is 50% larger in diameter than Earth's Moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's Ganymede and is larger than Mercury; yet Titan is only 40% as massive as Mercury, because Mercury is mainly iron and rock while much of Titan is ice, which is less dense.
Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan was the first known moon of Saturn and the sixth known planetary satellite (after Earth's moon and the four Galilean moons of Jupiter). Titan orbits Saturn at 20 Saturn radii or 1,200,000 km above Saturn's apparent surface. From Titan's surface, Saturn subtends an arc of 5.09 degrees, and if it were visible through the moon's thick atmosphere, it would appear 11.4 times larger in the sky, in diameter, than the Moon from Earth, which subtends 0.48° of arc.
Titan is primarily composed of ice and rocky material, with a rocky core surrounded by various layers of ice, including a crust of ice Ih and a subsurface layer of ammonia-rich liquid water. Much as with Venus before the Space Age, the dense opaque atmosphere prevented understanding of Titan's surface until the Cassini–Huygens mission in 2004 provided new information, including the discovery of liquid hydrocarbon lakes in Titan's polar regions and the discovery of its atmospheric super-rotation. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found. | Titan (moon) | Wikipedia | 419 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
The atmosphere of Titan is mainly nitrogen and methane; minor components lead to the formation of hydrocarbon clouds and heavy organonitrogen haze. Its climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle nearly resembles Earth's water cycle, albeit at a much lower temperature of about . Due to these factors, Titan is called the most Earth-like celestial object in the Solar System.
Discovery and naming
The Dutch astronomer Christiaan Huygens discovered Titan on March 25, 1655. Fascinated by Galileo's 1610 discovery of Jupiter's four largest moons and his advancements in telescope technology, Huygens, with the help of his elder brother Constantijn Huygens Jr., began building telescopes around 1650 and discovered the first observed moon orbiting Saturn with one of the telescopes they built.
Huygens named his discovery Saturni Luna (or Luna Saturni, Latin for "moon of Saturn"), publishing in the 1655 tract De Saturni Luna Observatio Nova (A New Observation of Saturn's Moon). After Giovanni Domenico Cassini published his discoveries of four more moons of Saturn between 1673 and 1686, astronomers began referring to these and Titan as Saturn I through V (with Titan then in fourth position). Other early epithets for Titan include "Saturn's ordinary satellite." The International Astronomical Union officially numbers Titan as "Saturn VI."
The name Titan, and the names of all seven satellites of Saturn then known, came from John Herschel (son of William Herschel, discoverer of two other Saturnian moons, Mimas and Enceladus), in his 1847 publication Results of Astronomical Observations Made during the Years 1834, 5, 6, 7, 8, at the Cape of Good Hope. Numerous small moons have been discovered around Saturn since then. Saturnian moons are named after mythological giants. The name Titan comes from the Titans, a race of immortals in Greek mythology. | Titan (moon) | Wikipedia | 449 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Formation
The regular moons of Jupiter and Saturn likely formed via co-accretion, similar to the process believed to have formed the planets in the Solar System. As the young gas giants formed, they were surrounded by discs of material that gradually coalesced into moons. While the four Galilean moons of Jupiter exist in highly regular, planet-like orbits, Titan overwhelmingly dominates Saturn's system and has a high orbital eccentricity not immediately explained by co-accretion alone. A proposed model for the formation of Titan is that Saturn's system began with a group of moons similar to Jupiter's Galilean moons, but that they were disrupted by a series of giant impacts, which would go on to form Titan. Saturn's mid-sized moons, such as Iapetus and Rhea, were formed from the debris of these collisions. Such a violent beginning would also explain Titan's orbital eccentricity. A 2014 analysis of Titan's atmospheric nitrogen suggested that it was possibly sourced from material similar to that found in the Oort cloud and not from sources present during the co-accretion of materials around Saturn.
Orbit and rotation
Titan orbits Saturn once every 15 days and 22 hours. Like Earth's Moon and many of the satellites of the giant planets, its rotational period (its day) is identical to its orbital period; Titan is tidally locked in synchronous rotation with Saturn, and permanently shows one face to the planet. Longitudes on Titan are measured westward, starting from the meridian passing through this point. Its orbital eccentricity is 0.0288, and the orbital plane is inclined 0.348 degrees relative to the Saturnian equator.
The small and irregularly shaped satellite Hyperion is locked in a 3:4 orbital resonance with Titan—that is, Hyperion orbits three times for every four times Titan orbits. Hyperion probably formed in a stable orbital island, whereas the massive Titan absorbed or ejected any other bodies that made close approaches.
Bulk characteristics | Titan (moon) | Wikipedia | 405 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Titan is 5,149.46 km (3,199.73 mi) in diameter; it is 6% larger than the planet Mercury and 50% larger than Earth's Moon. Titan is the tenth-largest object known in the Solar system, including the Sun. Before the arrival of Voyager 1 in 1980, Titan was thought to be slightly larger than Ganymede, which has a diameter 5,262 km (3,270 mi), and thus the largest moon in the Solar System. This was an overestimation caused by Titan's dense, opaque atmosphere, with a haze layer 100–200 km above its surface. This increases its apparent diameter. Titan's diameter and mass (and thus its density) are similar to those of the Jovian moons Ganymede and Callisto. Based on its bulk density of 1.881 g/cm3, Titan's composition is 40–60% rock, with the rest being water ice and other materials.
Titan is probably partially differentiated into distinct layers with a 3,400 km (2,100 mi) rocky center. This rocky center is believed to be surrounded by several layers composed of different crystalline forms of ice, and/or water. The exact structure depends heavily on the heat flux from within Titan itself, which is poorly constrained. The interior may still be hot enough for a liquid layer consisting of a "magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice. The heat flow from inside Titan may even be too high for high pressure ices to form, with the outermost layers instead consisting primarily of liquid water underneath a surface crust. The presence of ammonia allows water to remain liquid even at a temperature as low as (for eutectic mixture with water). | Titan (moon) | Wikipedia | 368 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
The Cassini probe discovered evidence for the layered structure in the form of natural extremely-low-frequency radio waves in Titan's atmosphere. Titan's surface is thought to be a poor reflector of extremely-low-frequency radio waves, so they may instead be reflecting off the liquid–ice boundary of a subsurface ocean. Surface features were observed by the Cassini spacecraft to systematically shift by up to 30 km (19 mi) between October 2005 and May 2007, which suggests that the crust is decoupled from the interior, and provides additional evidence for an interior liquid layer. Further supporting evidence for a liquid layer and ice shell decoupled from the solid core comes from the way the gravity field varies as Titan orbits Saturn. Comparison of the gravity field with the RADAR-based topography observations also suggests that the ice shell may be substantially rigid.
Atmosphere
Titan is the only moon in the Solar System with an atmosphere denser than Earth's, with a surface pressure of , and it is one of only two moons whose atmospheres are able to support clouds, hazes, and weather—the other being Neptune's moon Triton. The presence of a significant atmosphere was first suspected by Catalan astronomer Josep Comas i Solà, who observed distinct limb darkening on Titan in 1903. Due to the extensive, hazy atmosphere, Titan was once thought to be the largest moon in the Solar System until the Voyager missions revealed that Ganymede is slightly larger. The haze also shrouded Titan's surface from view, so direct images of its surface could not be taken until the Cassini–Huygens mission in 2004. | Titan (moon) | Wikipedia | 330 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
The primary constituents of Titan's atmosphere are nitrogen, methane, and hydrogen. The precise atmospheric composition varies depending on altitude and latitude due to methane cycling between a gas and a liquid in Titan's lower atmospherethe methane cycle. Nitrogen is the most abundant gas, with a concentration of around 98.6% in the stratosphere that decreases to 95.1% in the troposphere. Direct observations by the Huygens probe determined that methane concentrations are highest near the surface, with a concentration of 4.92% that remains relatively constant up to 8 km (5.0 mi) above the surface. Methane concentrations then gradually decrease with increasing altitude, down to a concentration of 1.41% in the stratosphere. Methane also increases in concentration near Titan's winter pole, probably due to evaporation from the surface in high-latitude regions. Hydrogen is the third-most abundant gas, with a concentration of around 0.1%. There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene, and propane, and other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, argon, and helium. The hydrocarbons are thought to form in Titan's upper atmosphere in reactions resulting from the breakup of methane by the Sun's ultraviolet light, producing a thick orange smog.
Energy from the Sun should have converted all traces of methane in Titan's atmosphere into more complex hydrocarbons within 50 million years—a short time compared to the age of the Solar System. This suggests that methane must be replenished by a reservoir on or within Titan itself. The ultimate origin of the methane in its atmosphere may be its interior, released via eruptions from cryovolcanoes.
On April 3, 2013, NASA reported that complex organic chemicals, collectively called tholins, likely arise on Titan, based on studies simulating the atmosphere of Titan.
On June 6, 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan. | Titan (moon) | Wikipedia | 445 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
On September 30, 2013, propene was detected in the atmosphere of Titan by NASA's Cassini spacecraft, using its composite infrared spectrometer (CIRS). This is the first time propene has been found on any moon or planet other than Earth and is the first chemical found by the CIRS. The detection of propene fills a mysterious gap in observations that date back to NASA's Voyager 1 spacecraft's first close planetary flyby of Titan in 1980, during which it was discovered that many of the gases that make up Titan's brown haze were hydrocarbons, theoretically formed via the recombination of radicals created by the Sun's ultraviolet photolysis of methane.
Climate
Titan's surface temperature is about . At this temperature, water ice has an extremely low vapor pressure, so the little water vapor present appears limited to the stratosphere. Titan receives about 1% as much sunlight as Earth. Before sunlight reaches the surface, about 90% has been absorbed by the thick atmosphere, leaving only 0.1% of the amount of light Earth receives.
Atmospheric methane creates a greenhouse effect on Titan's surface, without which Titan would be much colder. Conversely, haze in Titan's atmosphere contributes to an anti-greenhouse effect by absorbing sunlight, canceling a portion of the greenhouse effect and making its surface significantly colder than its upper atmosphere.
Titan's clouds, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze. The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto its surface.
Clouds typically cover 1% of Titan's disk, though outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. One hypothesis asserts that the southern clouds are formed when heightened levels of sunlight during the southern summer generate uplift in the atmosphere, resulting in convection. This explanation is complicated by the fact that cloud formation has been observed not only after the southern summer solstice but also during mid-spring. Increased methane humidity at the south pole possibly contributes to the rapid increases in cloud size. It was summer in Titan's southern hemisphere until 2010, when Saturn's orbit, which governs Titan's motion, moved Titan's northern hemisphere into the sunlight. When the seasons switch, it is expected that ethane will begin to condense over the south pole.
Surface features | Titan (moon) | Wikipedia | 499 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
The surface of Titan has been described as "complex, fluid-processed, [and] geologically young". Titan has been around since the Solar System's formation, but its surface is much younger, between 100 million and 1 billion years old. Geological processes may have reshaped Titan's surface. Titan's atmosphere is four times as thick as Earth's, making it difficult for astronomical instruments to image its surface in the visible light spectrum. The Cassini spacecraft used infrared instruments, radar altimetry and synthetic aperture radar (SAR) imaging to map portions of Titan during its close fly-bys. The first images revealed a diverse geology, with both rough and smooth areas. There are features that may be volcanic in origin, disgorging water mixed with ammonia onto the surface. There is also evidence that Titan's ice shell may be substantially rigid, which would suggest little geologic activity.
There are also streaky features, some of them hundreds of kilometers in length, that appear to be caused by windblown particles. Examination has also shown the surface to be relatively smooth; the few features that seem to be impact craters appeared to have been partially filled in, perhaps by raining hydrocarbons or cryovolcanism. Radar altimetry suggests topographical variation is low, typically no more than 150 meters. Occasional elevation changes of 500 meters have been discovered and Titan has mountains that sometimes reach several hundred meters to more than one kilometer in height.
Titan's surface is marked by broad regions of bright and dark terrain. These include Xanadu, a large, reflective equatorial area about the size of Australia. It was first identified in infrared images from the Hubble Space Telescope in 1994, and later viewed by the Cassini spacecraft. The convoluted region is filled with hills and cut by valleys and chasms. It is criss-crossed in places by dark lineaments—sinuous topographical features resembling ridges or crevices. These may represent tectonic activity, which would indicate that Xanadu is geologically young. Alternatively, the lineaments may be liquid-formed channels, suggesting old terrain that has been cut through by stream systems. There are dark areas of similar size elsewhere on Titan, observed from the ground and by Cassini; at least one of these, Ligeia Mare, Titan's second-largest sea, is almost a pure methane sea.
Lakes and seas | Titan (moon) | Wikipedia | 494 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Following the Voyager flybys, Titan was confirmed to have an atmosphere capable of supporting liquid hydrocarbons on its surface. However, the first tentative detection only came in 1995, when data from the Hubble Space Telescope and radar observations suggested expansive hydrocarbon lakes, seas, or oceans. The existence of liquid hydrocarbons on Titan was finally confirmed in situ by the Cassini orbiter, with the Cassini mission team announcing "definitive evidence of the presence of lakes filled with liquid methane on Saturn's moon Titan" in January 2007.
The observed lakes and seas of Titan are largely restricted to its polar regions, where colder temperatures allow the presence of permanent liquid hydrocarbons. Near Titan's north pole are Kraken Mare, the largest sea; Ligeia Mare, the second-largest sea; and Punga Mare, each filling broad depressions and cumulatively representing roughly 80% of Titan's sea and lake coverage— 691,000 km² (267,000 sq mi) combined. All three maria's sea levels are similar, suggesting that they may be hydraulically connected. The southern polar region, meanwhile, hosts four dry broad depressions, potentially representing dried-up seabeds. Additional smaller lakes occupy Titan's polar regions, covering a cumulative surface area of 215,000 km² (83,000 sq mi). Lakes in Titan's lower-latitude and equatorial regions have been proposed, though none have been confirmed; seasonal or transient equatorial lakes may pool following large rainstorms. Cassini RADAR data has been used to conduct bathymetry of Titan's seas and lakes. Using detected subsurface reflections, the measured maximum depth of Ligeia Mare is roughly , and that of Ontario Lacus is roughly . | Titan (moon) | Wikipedia | 356 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Titan's lakes and seas are dominated by methane (), with smaller amounts of ethane () and dissolved nitrogen (). The fraction of these components varies across different bodies: observations of Ligeia Mare are consistent with 71% , 12% , and 17% by volume; whilst Ontario Lacus is consistent with 49% , 41% , and 10% by volume. As Titan is synchronously locked with Saturn, there exists a permanent tidal bulge of roughly at the sub- and anti-Saturnian points. Titan's orbital eccentricity means that tidal acceleration varies by 9%, though the long orbital period means that these tidal cycles are very gradual. A team of researchers led by Ralph D. Lorenz evaluated that the tidal range of Titan's major seas are around .
Tectonics and cryovolcanism
Through Cassini RADAR mapping of Titan's surface, numerous landforms have been interpreted as candidate cryovolcanic and tectonic features by multiple authors. A 2016 analysis of mountainous ridges on Titan revealed that ridges are concentrated in Titan's equatorial regions, implying that ridges either form more frequently in or are better preserved in low-latitude regions. The ridges—primarily oriented east to west—are linear to arcuate in shape, with the authors of the analysis comparing them to terrestrial fold belts indicative of horizontal compression or convergence. They note that the global distribution of Titan's ridges could be indicative of global contraction, with a thickened ice shell causing regional uplift. | Titan (moon) | Wikipedia | 306 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
The identification of cryovolcanic features on Titan remains controversial and inconclusive, primarily due to limitations of Cassini imagery and coverage. Cassini RADAR and VIMS imagery revealed several candidate cryovolcanic features, particularly flow-like terrains in western Xanadu and steep-sided lakes in the northern hemisphere that resemble maar craters on Earth, which are created by explosive subterranean eruptions. The likeliest cryovolcano features is a complex of landforms that includes two mountains, Doom Mons and Erebor Mons; a large depression, Sotra Patera; and a system of flow-like features, Mohini Fluctus. Between 2005 and 2006, parts of Sotra Patera and Mohini Fluctus became significantly brighter whilst the surrounding plains remained unchanged, potentially indicative of ongoing cryovolcanic activity. Indirect lines of evidence for cryovolcanism include the presence of Argon-40 in Titan's atmosphere. Radiogenic 40Ar is sourced from the decay of 40K, and has likely been produced within Titan over the course of billions of years within its rocky core. 40Ar's presence in Titan's atmosphere is thus supportive of active geology on Titan, with cryovolcanism being one possible method of bringing the isotope up from the interior.
Impact craters
Titan's surface has comparatively few impact craters, with erosion, tectonics, and cryovolcanism possibly working to erase them over time. Compared to the craters of similarly sized and structured Ganymede and Callisto, those of Titan are much shallower. Many have dark floors of sediment; geomorphological analysis of impact craters largely suggests that erosion and burial are the primary mechanisms of crater modification. Titan's craters are also not evenly distributed, as the polar regions are almost devoid of any identified craters whilst the majority are located in the equatorial dune fields. This inequality may be the result of oceans that once occupied Titan's poles, polar sediment deposition by past rainfall, or increased rates of erosion in the polar regions.
Plains and dunes
The majority of Titan's surface is covered by plains. Of the several types of plains observed, the most extensive are the Undifferentiated Plains that encompass vast, radar-dark uniform regions.
These mid-latitude plains—located largely between 20 and 60° north or south—appear younger than all major geological features except dunes and several craters. The Undifferentiated Plains likely were formed by wind-driven processes and composed of organic-rich sediment. | Titan (moon) | Wikipedia | 512 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Another extensive type of terrain on Titan are sand dunes, grouped together into vast dune fields or "sand seas" located within 30° north or south. Titanian dunes are typically 1–2 km (0.62–1.24 mi) wide and spaced 1–4 (0.62–2.49 mi) apart, with some individual dunes over 100 km (62 mi) in length. Limited radar-derived height data suggests that the dunes are tall, with the dunes appearing dark in Cassini SAR imagery. Interactions between the dunes and obstacle features, such as mountains, indicate that sand is generally transported in a west-to-east direction. The sand that constructs the dunes is dominated by organic material, probably from Titan's atmosphere; possible sources of sand include river channels or the Undifferentiated Plains.
Observation and exploration
Titan is never visible to the naked eye, but can be observed through small telescopes or strong binoculars. Amateur observation is difficult because of the proximity of Titan to Saturn's brilliant globe and ring system; an occulting bar, covering part of the eyepiece and used to block the bright planet, greatly improves viewing. Titan has a maximum apparent magnitude of +8.2, and mean opposition magnitude 8.4. This compares to +4.6 for the similarly sized Ganymede, in the Jovian system.
Observations of Titan prior to the space age were limited. In 1907 Catalan astronomer Josep Comas i Solà observed limb darkening of Titan, the first evidence that the body has an atmosphere. In 1944 Gerard P. Kuiper used a spectroscopic technique to detect an atmosphere of methane.
Pioneer and Voyager
The first probe to visit the Saturnian system was Pioneer 11 in 1979, which revealed that Titan was probably too cold to support life. It took images of Titan, including Titan and Saturn together in mid to late 1979. The quality was soon surpassed by the two Voyagers. | Titan (moon) | Wikipedia | 392 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Titan was examined by both Voyager 1 and 2 in 1980 and 1981, respectively. Voyager 1's trajectory was designed to provide an optimized Titan flyby, during which the spacecraft was able to determine the density, composition, and temperature of the atmosphere, and obtain a precise measurement of Titan's mass. Atmospheric haze prevented direct imaging of the surface, though in 2004 intensive digital processing of images taken through Voyager 1's orange filter did reveal hints of the light and dark features now known as Xanadu and Shangri-la, which had been observed in the infrared by the Hubble Space Telescope. Voyager 2, which would have been diverted to perform the Titan flyby if Voyager 1 had been unable to, did not pass near Titan and continued on to Uranus and Neptune.
Cassini–Huygens
The Cassini–Huygens spacecraft reached Saturn on July 1, 2004, and began the process of mapping Titan's surface by radar. A joint project of the European Space Agency (ESA) and NASA, Cassini–Huygens proved a very successful mission. The Cassini probe flew by Titan on October 26, 2004, and took the highest-resolution images ever of Titan's surface, at only 1,200 km (750 mi) , discerning patches of light and dark that would be invisible to the human eye.
On July 22, 2006, Cassini made its first targeted, close fly-by at 950 km (590 mi) from Titan; the closest flyby was at 880 km (550 mi) on June 21, 2010. Liquid has been found in abundance on the surface in the north polar region, in the form of many lakes and seas discovered by Cassini.
Huygens landing
Huygens was an atmospheric probe that touched down on Titan on January 14, 2005, discovering that many of its surface features seem to have been formed by fluids at some point in the past. Titan is the most distant body from Earth to have a space probe land on its surface. | Titan (moon) | Wikipedia | 409 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
The Huygens probe landed just off the easternmost tip of a bright region now called Adiri. The probe photographed pale hills with dark "rivers" running down to a dark plain. Current understanding is that the hills (also referred to as highlands) are composed mainly of water ice. Dark organic compounds, created in the upper atmosphere by the ultraviolet radiation of the Sun, may rain from Titan's atmosphere. They are washed down the hills with the methane rain and are deposited on the plains over geological time scales.
After landing, Huygens photographed a dark plain covered in small rocks and pebbles, which are composed of water ice. The two rocks just below the middle of the image on the right are smaller than they may appear: the left-hand one is 15 centimeters across, and the one in the center is 4 centimeters across, at a distance of about 85 centimeters from Huygens. There is evidence of erosion at the base of the rocks, indicating possible fluvial activity. The ground surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice.
In March 2007, NASA, ESA, and COSPAR decided to name the Huygens landing site the Hubert Curien Memorial Station in memory of the former president of the ESA.
Dragonfly
The Dragonfly mission, developed and operated by the Johns Hopkins Applied Physics Laboratory, is scheduled to launch in July 2028. It consists of a large drone powered by an RTG to fly in the atmosphere of Titan as New Frontiers 4. Its instruments will study how far prebiotic chemistry may have progressed. The mission is planned to arrive at Titan in the mid-2030s.
Proposed or conceptual missions | Titan (moon) | Wikipedia | 337 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
There have been several conceptual missions proposed in recent years for returning a robotic space probe to Titan. Initial conceptual work has been completed for such missions by NASA (and JPL), and ESA. At present, none of these proposals have become funded missions. The Titan Saturn System Mission (TSSM) was a joint NASA/ESA proposal for exploration of Saturn's moons. It envisions a hot-air balloon floating in Titan's atmosphere for six months. It was competing against the Europa Jupiter System Mission (EJSM) proposal for funding. In February 2009 it was announced that ESA/NASA had given the EJSM mission priority ahead of the TSSM. The proposed Titan Mare Explorer (TiME) was a low-cost lander that would splash down in Ligeia Mare in Titan's northern hemisphere. The probe would float whilst investigating Titan's hydrocarbon cycle, sea chemistry, and Titan's origins. It was selected for a Phase-A design study in 2011 as a candidate mission for the 12th NASA Discovery Program opportunity, but was not selected for flight.
Another mission to Titan proposed in early 2012 by Jason Barnes, a scientist at the University of Idaho, is the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR): an uncrewed plane (or drone) that would fly through Titan's atmosphere and take high-definition images of the surface of Titan. NASA did not approve the requested $715 million, and the future of the project is uncertain.
A conceptual design for another lake lander was proposed in late 2012 by the Spanish-based private engineering firm SENER and the Centro de Astrobiología in Madrid. The concept probe is called Titan Lake In-situ Sampling Propelled Explorer (TALISE). The major difference compared to the TiME probe would be that TALISE is envisioned with its own propulsion system and would therefore not be limited to simply drifting on the lake when it splashes down.
A Discovery Program contestant for its mission #13 is Journey to Enceladus and Titan (JET), an astrobiology Saturn orbiter that would assess the habitability potential of Enceladus and Titan.
In 2015, the NASA Innovative Advanced Concepts program (NIAC) awarded a Phase II grant to a design study of a Titan Submarine to explore the seas of Titan.
Prebiotic conditions and life | Titan (moon) | Wikipedia | 478 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Titan is thought to be a prebiotic environment rich in complex organic compounds, but its surface is in a deep freeze at so it is currently understood that life cannot exist on the moon's frigid surface. However, Titan seems to contain a global ocean beneath its ice shell, and within this ocean, conditions are potentially suitable for microbial life.
The Cassini–Huygens mission was not equipped to provide evidence for biosignatures or complex organic compounds; it showed an environment on Titan that is similar, in some ways, to ones hypothesized for the primordial Earth. Scientists surmise that the atmosphere of early Earth was similar in composition to the current atmosphere on Titan, with the important exception of a lack of water vapor on Titan.
Formation of complex molecules
The Miller–Urey experiment and several following experiments have shown that with an atmosphere similar to that of Titan and the addition of UV radiation, complex molecules and polymer substances like tholins can be generated. The reaction starts with dissociation of nitrogen and methane, forming hydrogen cyanide and acetylene. Further reactions have been studied extensively.
It has been reported that when energy was applied to a combination of gases like those in Titan's atmosphere, five nucleotide bases, the building blocks of DNA and RNA, were among the many compounds produced. In addition, amino acids—the building blocks of protein—were found. It was the first time nucleotide bases and amino acids had been found in such an experiment without liquid water being present.
Possible subsurface habitats
Laboratory simulations have led to the suggestion that enough organic material exists on Titan to start a chemical evolution analogous to what is thought to have started life on Earth. The analogy assumes the presence of liquid water for longer periods than is currently observable; several hypotheses postulate that liquid water from an impact could be preserved under a frozen isolation layer. It has also been hypothesized that liquid-ammonia oceans could exist deep below the surface. Another model suggests an ammonia–water solution as much as 200 km (120) deep beneath a water-ice crust with conditions that, although extreme by terrestrial standards, are such that life could survive. Heat transfer between the interior and upper layers would be critical in sustaining any subsurface oceanic life. Detection of microbial life on Titan would depend on its biogenic effects, with the atmospheric methane and nitrogen examined.
Methane and life at the surface | Titan (moon) | Wikipedia | 498 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
It has been speculated that life could exist in the lakes of liquid methane on Titan, just as organisms on Earth live in water. Such organisms would inhale H2 in place of O2, metabolize it with acetylene instead of glucose, and exhale methane instead of carbon dioxide. However, such hypothetical organisms would be required to metabolize at a deep freeze temperature of .
All life forms on Earth (including methanogens) use liquid water as a solvent; it is speculated that life on Titan might instead use a liquid hydrocarbon, such as methane or ethane, although water is a stronger solvent than methane. Water is also more chemically reactive, and can break down large organic molecules through hydrolysis. A life form whose solvent was a hydrocarbon would not face the risk of its biomolecules being destroyed in this way.
In 2005, astrobiologist Chris McKay argued that if methanogenic life did exist on the surface of Titan, it would likely have a measurable effect on the mixing ratio in the Titan troposphere: levels of hydrogen and acetylene would be measurably lower than otherwise expected. Assuming metabolic rates similar to those of methanogenic organisms on Earth, the concentration of molecular hydrogen would drop by a factor of 1000 on the Titanian surface solely due to a hypothetical biological sink. McKay noted that, if life is indeed present, the low temperatures on Titan would result in very slow metabolic processes, which could conceivably be hastened by the use of catalysts similar to enzymes. He also noted that the low solubility of organic compounds in methane presents a more significant challenge to any possible form of life. Forms of active transport, and organisms with large surface-to-volume ratios could theoretically lessen the disadvantages posed by this fact. | Titan (moon) | Wikipedia | 369 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
In 2010, Darrell Strobel, from Johns Hopkins University, identified a greater abundance of molecular hydrogen in the upper atmospheric layers of Titan compared to the lower layers, arguing for a downward flow at a rate of roughly 1028 molecules per second and disappearance of hydrogen near Titan's surface; as Strobel noted, his findings were in line with the effects McKay had predicted if methanogenic life-forms were present. The same year, another study showed low levels of acetylene on Titan's surface, which were interpreted by McKay as consistent with the hypothesis of organisms consuming hydrocarbons. Although restating the biological hypothesis, he cautioned that other explanations for the hydrogen and acetylene findings are more likely: the possibilities of yet unidentified physical or chemical processes (e.g. a surface catalyst accepting hydrocarbons or hydrogen), or flaws in the current models of material flow. Composition data and transport models need to be substantiated, etc. Even so, despite saying that a non-biological catalytic explanation would be less startling than a biological one, McKay noted that the discovery of a catalyst effective at would still be significant. With regards to the acetylene findings, Mark Allen, the principal investigator with the NASA Astrobiology Institute Titan team, provided a speculative, non-biological explanation: sunlight or cosmic rays could transform the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.
As NASA notes in its news article on the June 2010 findings: "To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere." As the NASA statement also says: "some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface."
In February 2015, a hypothetical cell membrane capable of functioning in liquid methane at cryogenic temperatures (deep freeze) conditions was modeled. Composed of small molecules containing carbon, hydrogen, and nitrogen, it would have the same stability and flexibility as cell membranes on Earth, which are composed of phospholipids, compounds of carbon, hydrogen, oxygen, and phosphorus. This hypothetical cell membrane was termed an "azotosome", a combination of "azote", French for nitrogen, and "liposome". | Titan (moon) | Wikipedia | 481 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Obstacles
Despite these biological possibilities, there are formidable obstacles to life on Titan, and any analogy to Earth is inexact. At a vast distance from the Sun, Titan is frigid, and its atmosphere lacks CO2. At Titan's surface, water exists only in solid form. Because of these difficulties, scientists such as Jonathan Lunine have viewed Titan less as a likely habitat for life than as an experiment for examining hypotheses on the conditions that prevailed prior to the appearance of life on Earth. Although life itself may not exist, the prebiotic conditions on Titan and the associated organic chemistry remain of great interest in understanding the early history of the terrestrial biosphere. Using Titan as a prebiotic experiment involves not only observation through spacecraft, but laboratory experiments, and chemical and photochemical modeling on Earth.
Panspermia hypothesis
It is hypothesized that large asteroid and cometary impacts on Earth's surface may have caused fragments of microbe-laden rock to escape Earth's gravity, suggesting the possibility of panspermia. Calculations indicate that these would encounter many of the bodies in the Solar System, including Titan. On the other hand, Jonathan Lunine has argued that any living things in Titan's cryogenic hydrocarbon lakes would need to be so different chemically from Earth life that it would not be possible for one to be the ancestor of the other.
Future conditions
Conditions on Titan could become far more habitable in the far future. Five billion years from now, as the Sun becomes a sub-red giant, its surface temperature could rise enough for Titan to support liquid water on its surface, making it habitable. As the Sun's ultraviolet output decreases, the haze in Titan's upper atmosphere will be depleted, lessening the anti-greenhouse effect on the surface and enabling the greenhouse created by atmospheric methane to play a far greater role. These conditions together could create a habitable environment, and could persist for several hundred million years. This is proposed to have been sufficient time for simple life to spawn on Earth, though the higher viscosity of ammonia-water solutions coupled with low temperatures would cause chemical reactions to proceed more slowly on Titan. | Titan (moon) | Wikipedia | 440 | 47402 | https://en.wikipedia.org/wiki/Titan%20%28moon%29 | Physical sciences | Solar System | null |
Instrumentation is a collective term for measuring instruments, used for indicating, measuring, and recording physical quantities. It is also a field of study about the art and science about making measurement instruments, involving the related areas of metrology, automation, and control theory. The term has its origins in the art and science of scientific instrument-making.
Instrumentation can refer to devices as simple as direct-reading thermometers, or as complex as multi-sensor components of industrial control systems. Instruments can be found in laboratories, refineries, factories and vehicles, as well as in everyday household use (e.g., smoke detectors and thermostats).
Measurement parameters
Instrumentation is used to measure many parameters (physical values), including:
Pressure, either differential or static
Flow
Temperature
Levels of liquids, etc.
Moisture or humidity
Density
Viscosity
ionising radiation
Frequency
Current
Voltage
Inductance
Capacitance
Resistivity
Chemical composition
Chemical properties
Toxic gases
Position
Vibration
Weight
History
The history of instrumentation can be divided into several phases.
Pre-industrial
Elements of industrial instrumentation have long histories. Scales for comparing weights and simple pointers to indicate position are ancient technologies. Some of the earliest measurements were of time. One of the oldest water clocks was found in the tomb of the ancient Egyptian pharaoh Amenhotep I, buried around 1500 BCE. Improvements were incorporated in the clocks. By 270 BCE they had the rudiments of an automatic control system device.
In 1663 Christopher Wren presented the Royal Society with a design for a "weather clock". A drawing shows meteorological sensors moving pens over paper driven by clockwork. Such devices did not become standard in meteorology for two centuries. The concept has remained virtually unchanged as evidenced by pneumatic chart recorders, where a pressurized bellows displaces a pen. Integrating sensors, displays, recorders, and controls was uncommon until the industrial revolution, limited by both need and practicality.
Early industrial
Early systems used direct process connections to local control panels for control and indication, which from the early 1930s saw the introduction of pneumatic transmitters and automatic 3-term (PID) controllers. | Instrumentation | Wikipedia | 431 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
The ranges of pneumatic transmitters were defined by the need to control valves and actuators in the field. Typically, a signal ranged from 3 to 15 psi (20 to 100kPa or 0.2 to 1.0 kg/cm2) as a standard, was standardized with 6 to 30 psi occasionally being used for larger valves.
Transistor electronics enabled wiring to replace pipes, initially with a range of 20 to 100mA at up to 90V for loop powered devices, reducing to 4 to 20mA at 12 to 24V in more modern systems. A transmitter is a device that produces an output signal, often in the form of a 4–20 mA electrical current signal, although many other options using voltage, frequency, pressure, or ethernet are possible. The transistor was commercialized by the mid-1950s.
Instruments attached to a control system provided signals used to operate solenoids, valves, regulators, circuit breakers, relays and other devices. Such devices could control a desired output variable, and provide either remote monitoring or automated control capabilities.
Each instrument company introduced their own standard instrumentation signal, causing confusion until the 4–20 mA range was used as the standard electronic instrument signal for transmitters and valves. This signal was eventually standardized as ANSI/ISA S50, "Compatibility of Analog Signals for Electronic Industrial Process Instruments", in the 1970s. The transformation of instrumentation from mechanical pneumatic transmitters, controllers, and valves to electronic instruments reduced maintenance costs as electronic instruments were more dependable than mechanical instruments. This also increased efficiency and production due to their increase in accuracy. Pneumatics enjoyed some advantages, being favored in corrosive and explosive atmospheres.
Automatic process control | Instrumentation | Wikipedia | 344 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
In the early years of process control, process indicators and control elements such as valves were monitored by an operator, that walked around the unit adjusting the valves to obtain the desired temperatures, pressures, and flows. As technology evolved pneumatic controllers were invented and mounted in the field that monitored the process and controlled the valves. This reduced the amount of time process operators needed to monitor the process. Latter years, the actual controllers were moved to a central room and signals were sent into the control room to monitor the process and outputs signals were sent to the final control element such as a valve to adjust the process as needed. These controllers and indicators were mounted on a wall called a control board. The operators stood in front of this board walking back and forth monitoring the process indicators. This again reduced the number and amount of time process operators were needed to walk around the units. The most standard pneumatic signal level used during these years was 3–15 psig.
Large integrated computer-based systems
Process control of large industrial plants has evolved through many stages. Initially, control would be from panels local to the process plant. However, this required a large manpower resource to attend to these dispersed panels, and there was no overall view of the process. The next logical development was the transmission of all plant measurements to a permanently staffed central control room. Effectively this was the centralization of all the localized panels, with the advantages of lower manning levels and easy overview of the process. Often the controllers were behind the control room panels, and all automatic and manual control outputs were transmitted back to plant.
However, whilst providing a central control focus, this arrangement was inflexible as each control loop had its own controller hardware, and continual operator movement within the control room was required to view different parts of the process. With coming of electronic processors and graphic displays it became possible to replace these discrete controllers with computer-based algorithms, hosted on a network of input/output racks with their own control processors. These could be distributed around plant, and communicate with the graphic display in the control room or rooms. The distributed control concept was born. | Instrumentation | Wikipedia | 424 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
The introduction of DCSs and SCADA allowed easy interconnection and re-configuration of plant controls such as cascaded loops and interlocks, and easy interfacing with other production computer systems. It enabled sophisticated alarm handling, introduced automatic event logging, removed the need for physical records such as chart recorders, allowed the control racks to be networked and thereby located locally to plant to reduce cabling runs, and provided high level overviews of plant status and production levels.
Application
In some cases, the sensor is a very minor element of the mechanism. Digital cameras and wristwatches might technically meet the loose definition of instrumentation because they record and/or display sensed information. Under most circumstances neither would be called instrumentation, but when used to measure the elapsed time of a race and to document the winner at the finish line, both would be called instrumentation.
Household
A very simple example of an instrumentation system is a mechanical thermostat, used to control a household furnace and thus to control room temperature. A typical unit senses temperature with a bi-metallic strip. It displays temperature by a needle on the free end of the strip. It activates the furnace by a mercury switch. As the switch is rotated by the strip, the mercury makes physical (and thus electrical) contact between electrodes.
Another example of an instrumentation system is a home security system. Such a system consists of
sensors (motion detection, switches to detect door openings), simple algorithms to detect intrusion, local control (arm/disarm) and remote monitoring of the system so that the police can be summoned. Communication is an inherent part of the design. | Instrumentation | Wikipedia | 332 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
Kitchen appliances use sensors for control.
A refrigerator maintains a constant temperature by actuating the cooling system when the temperature becomes too high.
An automatic ice machine makes ice until a limit switch is thrown.
Pop-up bread toasters allow the time to be set.
Non-electronic gas ovens will regulate the temperature with a thermostat controlling the flow of gas to the gas burner. These may feature a sensor bulb sited within the main chamber of the oven. In addition, there may be a safety cut-off flame supervision device: after ignition, the burner's control knob must be held for a short time in order for a sensor to become hot, and permit the flow of gas to the burner. If the safety sensor becomes cold, this may indicate the flame on the burner has become extinguished, and to prevent a continuous leak of gas the flow is stopped.
Electric ovens use a temperature sensor and will turn on heating elements when the temperature is too low. More advanced ovens will actuate fans in response to temperature sensors, to distribute heat or to cool.
A common toilet refills the water tank until a float closes the valve. The float is acting as a water level sensor.
Automotive
Modern automobiles have complex instrumentation. In addition to displays of engine rotational speed and vehicle linear speed, there are also displays of battery voltage and current, fluid levels, fluid temperatures, distance traveled, and feedback of various controls (turn signals, parking brake, headlights, transmission position). Cautions may be displayed for special problems (fuel low, check engine, tire pressure low, door ajar, seat belt unfastened). Problems are recorded so they can be reported to diagnostic equipment. Navigation systems can provide voice commands to reach a destination. Automotive instrumentation must be cheap and reliable over long periods in harsh environments. There may be independent airbag systems that contain sensors, logic and actuators. Anti-skid braking systems use sensors to control the brakes, while cruise control affects throttle position. A wide variety of services can be provided via communication links on the OnStar system. Autonomous cars (with exotic instrumentation) have been shown.
Aircraft
Early aircraft had a few sensors. "Steam gauges" converted air pressures into needle deflections that could be interpreted as altitude and airspeed. A magnetic compass provided a sense of direction. The displays to the pilot were as critical as the measurements. | Instrumentation | Wikipedia | 487 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
A modern aircraft has a far more sophisticated suite of sensors and displays, which are embedded into avionics systems. The aircraft may contain inertial navigation systems, global positioning systems, weather radar, autopilots, and aircraft stabilization systems. Redundant sensors are used for reliability. A subset of the information may be transferred to a crash recorder to aid mishap investigations. Modern pilot displays now include computer displays including head-up displays.
Air traffic control radar is a distributed instrumentation system. The ground part sends an electromagnetic pulse and receives an echo (at least). Aircraft carry transponders that transmit codes on reception of the pulse. The system displays an aircraft map location, an identifier and optionally altitude. The map location is based on sensed antenna direction and sensed time delay. The other information is embedded in the transponder transmission.
Laboratory instrumentation
Among the possible uses of the term is a collection of laboratory test equipment controlled by a computer through an IEEE-488 bus (also known as GPIB for General Purpose Instrument Bus or HPIB for Hewlitt Packard Instrument Bus). Laboratory equipment is available to measure many electrical and chemical quantities. Such a collection of equipment might be used to automate the testing of drinking water for pollutants.
Instrumentation engineering
Instrumentation engineering is the engineering specialization focused on the principle and operation of measuring instruments that are used in design and configuration of automated systems in areas such as electrical and pneumatic domains, and the control of quantities being measured.
They typically work for industries with automated processes, such as chemical or manufacturing plants, with the goal of improving system productivity, reliability, safety, optimization and stability.
To control the parameters in a process or in a particular system, devices such as microprocessors, microcontrollers or PLCs are used, but their ultimate aim is to control the parameters of a system. | Instrumentation | Wikipedia | 379 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
Instrumentation engineering is loosely defined because the required tasks are very domain dependent. An expert in the biomedical instrumentation of laboratory rats has very different concerns than the expert in rocket instrumentation. Common concerns of both are the selection of appropriate sensors based on size, weight, cost, reliability, accuracy, longevity, environmental robustness, and frequency response. Some sensors are literally fired in artillery shells. Others sense thermonuclear explosions until destroyed. Invariably sensor data must be recorded, transmitted or displayed. Recording rates and capacities vary enormously. Transmission can be trivial or can be clandestine, encrypted and low power in the presence of jamming. Displays can be trivially simple or can require consultation with human factors experts. Control system design varies from trivial to a separate specialty.
Instrumentation engineers are responsible for integrating the sensors with the recorders, transmitters, displays or control systems, and producing the Piping and instrumentation diagram for the process. They may design or specify installation, wiring and signal conditioning. They may be responsible for commissioning, calibration, testing and maintenance of the system.
In a research environment it is common for subject matter experts to have substantial instrumentation system expertise. An astronomer knows the structure of the universe and a great deal about telescopes – optics, pointing and cameras (or other sensing elements). That often includes the hard-won knowledge of the operational procedures that provide the best results. For example, an astronomer is often knowledgeable of techniques to minimize temperature gradients that cause air turbulence within the telescope.
Instrumentation technologists, technicians and mechanics specialize in troubleshooting, repairing and maintaining instruments and instrumentation systems.
Typical industrial transmitter signal types
Pneumatic loop (20-100KPa/3-15PSI) – Pneumatic
Current loop (4-20mA) – Electrical
HART – Data signalling, often overlaid on a current loop
Foundation Fieldbus – Data signalling
Profibus – Data signalling
Impact of modern development
Ralph Müller (1940) stated, "That the history of physical science is largely the history of instruments and their intelligent use is well known. The broad generalizations and theories which have arisen from time to time have stood or fallen on the basis of accurate measurement, and in several instances new instruments have had to be devised for the purpose. There is little evidence to show that the mind of modern man is superior to that of the ancients. His tools are incomparably better." | Instrumentation | Wikipedia | 489 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
Davis Baird has argued that the major change associated with Floris Cohens identification of a "fourth big scientific revolution" after World War II is the development of scientific instrumentation, not only in chemistry but across the sciences. In chemistry, the introduction of new instrumentation in the 1940s was "nothing less than a scientific and technological revolution" in which classical wet-and-dry methods of structural organic chemistry were discarded, and new areas of research opened up.
As early as 1954, W. A. Wildhack discussed both the productive and destructive potential inherent in process control.
The ability to make precise, verifiable and reproducible measurements of the natural world, at levels that were not previously observable, using scientific instrumentation, has "provided a different texture of the world". This instrumentation revolution fundamentally changes human abilities to monitor and respond, as is illustrated in the examples of DDT monitoring and the use of UV spectrophotometry and gas chromatography to monitor water pollutants. | Instrumentation | Wikipedia | 203 | 47403 | https://en.wikipedia.org/wiki/Instrumentation | Technology | Measuring instruments | null |
The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher (closer to outer space) and the cooler layers lower (closer to the planetary surface of the Earth). The increase of temperature with altitude is a result of the absorption of the Sun's ultraviolet (UV) radiation by the ozone layer, where ozone is exothermically photolyzed into oxygen in a cyclical fashion. This temperature inversion is in contrast to the troposphere, where temperature decreases with altitude, and between the troposphere and stratosphere is the tropopause border that demarcates the beginning of the temperature inversion.
Near the equator, the lower edge of the stratosphere is as high as , at mid-latitudes around , and at the poles about . Temperatures range from an average of near the tropopause to an average of near the mesosphere. Stratospheric temperatures also vary within the stratosphere as the seasons change, reaching particularly low temperatures in the polar night (winter). Winds in the stratosphere can far exceed those in the troposphere, reaching near in the Southern polar vortex.
Discovery
In 1902, Léon Teisserenc de Bort from France and Richard Assmann from Germany, in separate but coordinated publications and following years of observations, published the discovery of an isothermal layer at around 11–14 km (6.8-8.7 mi), which is the base of the lower stratosphere. This was based on temperature profiles from mostly unmanned and a few manned instrumented balloons.
Ozone layer | Stratosphere | Wikipedia | 362 | 47454 | https://en.wikipedia.org/wiki/Stratosphere | Physical sciences | Atmosphere: General | Earth science |
The mechanism describing the formation of the ozone layer was described by British mathematician and geophysicist Sydney Chapman in 1930, and is known as the Chapman cycle or ozone–oxygen cycle. Molecular oxygen absorbs high energy sunlight in the UV-C region, at wavelengths shorter than about 240 nm. Radicals produced from the homolytically split oxygen molecules combine with molecular oxygen to form ozone. Ozone in turn is photolysed much more rapidly than molecular oxygen as it has a stronger absorption that occurs at longer wavelengths, where the solar emission is more intense. Ozone (O3) photolysis produces O and O2. The oxygen atom product combines with atmospheric molecular oxygen to reform O3, releasing heat. The rapid photolysis and reformation of ozone heat the stratosphere, resulting in a temperature inversion. This increase of temperature with altitude is characteristic of the stratosphere; its resistance to vertical mixing means that it is stratified. Within the stratosphere temperatures increase with altitude (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 26.6°F).
This vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. However, exceptionally energetic convection processes, such as volcanic eruption columns and overshooting tops in severe supercell thunderstorms, may carry convection into the stratosphere on a very local and temporary basis. Overall, the attenuation of solar UV at wavelengths that damage DNA by the ozone layer allows life to exist on the surface of the planet outside of the ocean. All air entering the stratosphere must pass through the tropopause, the temperature minimum that divides the troposphere and stratosphere. The rising air is literally freeze dried; the stratosphere is a very dry place. The top of the stratosphere is called the stratopause, above which the temperature decreases with height.
Formation and destruction | Stratosphere | Wikipedia | 417 | 47454 | https://en.wikipedia.org/wiki/Stratosphere | Physical sciences | Atmosphere: General | Earth science |
Sydney Chapman gave a correct description of the source of stratospheric ozone and its ability to generate heat within the stratosphere; he also wrote that ozone may be destroyed by reacting with atomic oxygen, making two molecules of molecular oxygen. We now know that there are additional ozone loss mechanisms and that these mechanisms are catalytic, meaning that a small amount of the catalyst can destroy a great number of ozone molecules. The first is due to the reaction of hydroxyl radicals (•OH) with ozone. •OH is formed by the reaction of electrically excited oxygen atoms produced by ozone photolysis, with water vapor. While the stratosphere is dry, additional water vapor is produced in situ by the photochemical oxidation of methane (CH4). The HO2 radical produced by the reaction of OH with O3 is recycled to OH by reaction with oxygen atoms or ozone. In addition, solar proton events can significantly affect ozone levels via radiolysis with the subsequent formation of OH. Nitrous oxide (N2O) is produced by biological activity at the surface and is oxidised to NO in the stratosphere; the so-called NOx radical cycles also deplete stratospheric ozone. Finally, chlorofluorocarbon molecules are photolysed in the stratosphere releasing chlorine atoms that react with ozone giving ClO and O2. The chlorine atoms are recycled when ClO reacts with O in the upper stratosphere, or when ClO reacts with itself in the chemistry of the Antarctic ozone hole.
Paul J. Crutzen, Mario J. Molina and F. Sherwood Rowland were awarded the Nobel Prize in Chemistry in 1995 for their work describing the formation and decomposition of stratospheric ozone.
Aircraft flight
Commercial airliners typically cruise at altitudes of which is in the lower reaches of the stratosphere in temperate latitudes. This optimizes fuel efficiency, mostly due to the low temperatures encountered near the tropopause and low air density, reducing parasitic drag on the airframe. Stated another way, it allows the airliner to fly faster while maintaining lift equal to the weight of the plane. (The fuel consumption depends on the drag, which is related to the lift by the lift-to-drag ratio.) It also allows the airplane to stay above the turbulent weather of the troposphere.
The Concorde aircraft cruised at Mach 2 at about , and the SR-71 cruised at Mach 3 at , all within the stratosphere. | Stratosphere | Wikipedia | 512 | 47454 | https://en.wikipedia.org/wiki/Stratosphere | Physical sciences | Atmosphere: General | Earth science |
Because the temperature in the tropopause and lower stratosphere is largely constant with increasing altitude, very little convection and its resultant turbulence occurs there. Most turbulence at this altitude is caused by variations in the jet stream and other local wind shears, although areas of significant convective activity (thunderstorms) in the troposphere below may produce turbulence as a result of convective overshoot.
On October 24, 2014, Alan Eustace became the record holder for reaching the altitude record for a manned balloon at . Eustace also broke the world records for vertical speed skydiving, reached with a peak velocity of 1,321 km/h (822 mph) and total freefall distance of – lasting four minutes and 27 seconds.
Circulation and mixing
The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which the horizontal mixing of gaseous components proceeds much more rapidly than does vertical mixing. The overall circulation of the stratosphere is termed as Brewer-Dobson circulation, which is a single-celled circulation, spanning from the tropics up to the poles, consisting of the tropical upwelling of air from the tropical troposphere and the extra-tropical downwelling of air. Stratospheric circulation is a predominantly wave-driven circulation in that the tropical upwelling is induced by the wave force by the westward propagating Rossby waves, in a phenomenon called Rossby-wave pumping.
An interesting feature of stratospheric circulation is the quasi-biennial oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers, such as ozone or water vapor. | Stratosphere | Wikipedia | 383 | 47454 | https://en.wikipedia.org/wiki/Stratosphere | Physical sciences | Atmosphere: General | Earth science |
Another large-scale feature that significantly influences stratospheric circulation is the breaking planetary waves resulting in intense quasi-horizontal mixing in the midlatitudes. This breaking is much more pronounced in the winter hemisphere where this region is called the surf zone. This breaking is caused due to a highly non-linear interaction between the vertically propagating planetary waves and the isolated high potential vorticity region known as the polar vortex. The resultant breaking causes large-scale mixing of air and other trace gases throughout the midlatitude surf zone. The timescale of this rapid mixing is much smaller than the much slower timescales of upwelling in the tropics and downwelling in the extratropics.
During northern hemispheric winters, sudden stratospheric warmings, caused by the absorption of Rossby waves in the stratosphere, can be observed in approximately half of winters when easterly winds develop in the stratosphere. These events often precede unusual winter weather <ref>M.P. Baldwin and T.J. Dunkerton. 'Stratospheric Harbingers of Anomalous Weather Regimes , Science Magazine.</ref> and may even be responsible for the cold European winters of the 1960s.
Stratospheric warming of the polar vortex results in its weakening. When the vortex is strong, it keeps the cold, high-pressure air masses contained in the Arctic; when the vortex weakens, air masses move equatorward, and results in rapid changes of weather in the mid latitudes.
Upper-atmospheric lightning
Upper-atmospheric lightning is a family of short-lived electrical-breakdown phenomena that occur well above the altitudes of normal lightning and storm clouds. Upper-atmospheric lightning is believed to be electrically induced forms of luminous plasma. Lightning extending above the troposphere into the stratosphere is referred to as blue jet, and that reaching into the mesosphere as red sprite.
Life
Bacteria
Bacterial life survives in the stratosphere, making it a part of the biosphere. In 2001, dust was collected at a height of 41 kilometres in a high-altitude balloon experiment and was found to contain bacterial material when examined later in the laboratory. | Stratosphere | Wikipedia | 453 | 47454 | https://en.wikipedia.org/wiki/Stratosphere | Physical sciences | Atmosphere: General | Earth science |
Birds
Some bird species have been reported to fly at the upper levels of the troposphere. On November 29, 1973, a Rüppell's vulture (Gyps rueppelli) was ingested into a jet engine above the Ivory Coast. Bar-headed geese (Anser indicus'') sometimes migrate over Mount Everest, whose summit is . | Stratosphere | Wikipedia | 74 | 47454 | https://en.wikipedia.org/wiki/Stratosphere | Physical sciences | Atmosphere: General | Earth science |
The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of Earth's atmosphere, with temperatures below . The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at altitudes from above sea level, and the upper boundary (the mesopause) is usually from .
The stratosphere and mesosphere are sometimes collectively referred to as the "middle atmosphere", which spans altitudes approximately between above Earth's surface. The mesopause, at an altitude of , separates the mesosphere from the thermosphere—the second-outermost layer of Earth's atmosphere. On Earth, the mesopause nearly co-incides with the turbopause, below which different chemical species are well-mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform because the scale heights of different chemical species differ according to their molecular masses.
The term near space is also sometimes used to refer to altitudes within the mesosphere. This term does not have a technical definition, but typically refers to the region roughly between the Armstrong limit (about 62,000 ft or 19 km, above which humans require a pressure suit in order to survive) and the Kármán line (where astrodynamics must take over from aerodynamics in order to achieve flight); or, by another definition, to the space between the highest altitude commercial airliners fly at (about 40,000 ft (12.2 km)) and the lowest perigee of satellites being able to orbit the Earth (about 45 mi (73 km)). Some sources distinguish between the terms "near space" and "upper atmosphere", so that only the layers closest to the Kármán line are described as "near space". | Mesosphere | Wikipedia | 463 | 47460 | https://en.wikipedia.org/wiki/Mesosphere | Physical sciences | Atmosphere: General | Earth science |
Temperature
Within the mesosphere, temperature decreases with increasing height. This is a result of decreasing absorption of solar radiation by the rarefied atmosphere having a diminishing relative ozone concentration as altitude increases (ozone being the main absorber in the UV wavelengths that survived absorption by the thermosphere). Additionally, this is also a result of increasing cooling by CO2 radiative emission. The top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere. Temperatures in the upper mesosphere fall as low as about , varying according to latitude and season.
Dynamic features
The main most important features in this region are strong zonal (East-West) winds, atmospheric tides, internal atmospheric gravity waves (commonly called "gravity waves"), and planetary waves. Most of these tides and waves start in the troposphere and lower stratosphere, and propagate to the mesosphere. In the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate. This dissipation deposits momentum into the mesosphere and largely drives global circulation.
Noctilucent clouds are located in the mesosphere. The upper mesosphere is also the region of the ionosphere known as the D layer, which is only present during the day when some ionization occurs with nitric oxide being ionized by Lyman series-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the free electron and ion form back into a neutral molecule.
A deep sodium layer is located between . Made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the airglow. The sodium has an average concentration of 400,000 atoms per cubic centimetre. This band is regularly replenished by sodium sublimating from incoming meteors. Astronomers have begun utilizing this sodium band to create "guide stars" as part of the adaptive optical correction process used to produce ultra-sharp ground-based observations. Other metal layers, e.g. iron and potassium, exist in the upper mesosphere/lower thermosphere region as well. | Mesosphere | Wikipedia | 467 | 47460 | https://en.wikipedia.org/wiki/Mesosphere | Physical sciences | Atmosphere: General | Earth science |
Beginning in October 2018, a distinct type of aurora has been identified, originating in the mesosphere. Often referred to as 'dunes' due to their resemblance to sandy ripples on a beach, the green undulating lights extend toward the equator. They have been identified as originating about above the surface. Since auroras are caused by ultra-high-speed solar particles interacting with atmospheric molecules, the green color of these dunes has tentatively been explained by the interaction of those solar particles with oxygen molecules. The dunes therefore occur where mesospheric oxygen is more concentrated.
Millions of meteors enter the Earth's atmosphere, averaging 40,000 tons per year. The ablated material, called meteoric smoke, is thought to serve as condensation nuclei for noctilucent clouds.
Exploration
The mesosphere lies above altitude records for aircraft, while only the lowest few kilometers are accessible to balloons, for which the altitude record is . Meanwhile, the mesosphere is below the minimum altitude for orbital spacecraft due to high atmospheric drag. It has only been accessed through the use of sounding rockets, which are only capable of taking mesospheric measurements for a few minutes per mission. As a result, it is the least-understood part of the atmosphere, resulting in the humorous moniker ignorosphere. The presence of red sprites and blue jets (electrical discharges or lightning within the lower mesosphere), noctilucent clouds, and density shears within this poorly understood layer are of current scientific interest.
On February 1, 2003, broke up on reentry at about altitude, in the lower mesosphere, killing all seven crew members.
Phenomena in mesosphere and near space
Airglow
Atmospheric tides
Ionosphere
Meteors
Noctilucent clouds
Polar aurora
Sprite (lightning)
Upper atmospheric lightning (Transient luminous event) | Mesosphere | Wikipedia | 382 | 47460 | https://en.wikipedia.org/wiki/Mesosphere | Physical sciences | Atmosphere: General | Earth science |
The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the thermosphere thus constitutes the larger part of the ionosphere. Taking its name from the Greek θερμός (pronounced thermos) meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass (see turbosphere). Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to or more. Radiation causes the atmospheric particles in this layer to become electrically charged, enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375 mi) above sea level, the atmosphere turns into space, although, by the judging criteria set for the definition of the Kármán line (100 km), most of the thermosphere is part of space. The border between the thermosphere and exosphere is known as the thermopause.
The highly attenuated gas in this layer can reach . Despite the high temperature, an observer or object will experience low temperatures in the thermosphere, because the extremely low density of the gas (practically a hard vacuum) is insufficient for the molecules to conduct heat. A normal thermometer will read significantly below , at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact. In the anacoustic zone above , the density is so low that molecular interactions are too infrequent to permit the transmission of sound.
The dynamics of the thermosphere are dominated by atmospheric tides, which are driven predominantly by diurnal heating. Atmospheric waves dissipate above this level because of collisions between the neutral gas and the ionospheric plasma.
The thermosphere is uninhabited with the exception of the International Space Station, which orbits the Earth within the middle of the thermosphere between and the Tiangong space station, which orbits between . | Thermosphere | Wikipedia | 462 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
Neutral gas constituents
It is convenient to separate the atmospheric regions according to the two temperature minima at an altitude of about (the tropopause) and at about (the mesopause) (Figure 1). The thermosphere (or the upper atmosphere) is the height region above , while the region between the tropopause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near an altitude of and causes the ozone layer.
The density of the Earth's atmosphere decreases nearly exponentially with altitude. The total mass of the atmosphere is M = ρA H ≃ 1 kg/cm2 within a column of one square centimeter above the ground (with ρA = 1.29 kg/m3 the atmospheric density on the ground at z = 0 m altitude, and H ≃ 8 km the average atmospheric scale height). Eighty percent of that mass is concentrated within the troposphere. The mass of the thermosphere above about is only 0.002% of the total mass. Therefore, no significant energetic feedback from the thermosphere to the lower atmospheric regions can be expected.
Turbulence causes the air within the lower atmospheric regions below the turbopause at about to be a mixture of gases that does not change its composition. Its mean molecular weight is 29 g/mol with molecular oxygen (O2) and nitrogen (N2) as the two dominant constituents. Above the turbopause, however, diffusive separation of the various constituents is significant, so that each constituent follows its barometric height structure with a scale height inversely proportional to its molecular weight. The lighter constituents atomic oxygen (O), helium (He), and hydrogen (H) successively dominate above an altitude of about and vary with geographic location, time, and solar activity. The ratio
N2/O which is a measure of the electron density at the ionospheric F region is highly affected by these variations. These changes follow from the diffusion of the minor constituents through the major gas component during dynamic processes. | Thermosphere | Wikipedia | 430 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
The thermosphere contains an appreciable concentration of elemental sodium located in a thick band that occurs at the edge of the mesosphere, above Earth's surface. The sodium has an average concentration of 400,000 atoms per cubic centimeter. This band is regularly replenished by sodium sublimating from incoming meteors. Astronomers have begun using this sodium band to create "guide stars" as part of the optical correction process in producing ultra-sharp ground-based observations.
Energy input
Energy budget
The thermospheric temperature can be determined from density observations as well as from direct satellite measurements. The temperature vs. altitude z in Fig. 1 can be simulated by the so-called Bates profile:
(1)
with T∞ the exospheric temperature above about 400 km altitude,
To = 355 K, and zo = 120 km reference temperature and height, and s an empirical parameter depending on T∞ and decreasing with T∞. That formula is derived from a simple equation of heat conduction. One estimates a total heat input of qo≃ 0.8 to 1.6 mW/m2 above zo = 120 km altitude. In order to obtain equilibrium conditions, that heat input qo above zo is lost to the lower atmospheric regions by heat conduction.
The exospheric temperature T∞ is a fair measurement of the solar XUV radiation. Since solar radio emission F at 10.7 cm wavelength is a good indicator of solar activity, one can apply the empirical formula for quiet magnetospheric conditions.
(2)
with T∞ in K, Fo in 10−2 W m−2 Hz−1 (the Covington index) a value of F averaged over several solar cycles. The Covington index varies typically between 70 and 250 during a solar cycle, and never drops below about 50. Thus, T∞ varies between about 740 and 1350 K. During very quiet magnetospheric conditions, the still continuously flowing magnetospheric energy input contributes by about 250 K to the residual temperature of 500 K in eq.(2). The rest of 250 K in eq.(2) can be attributed to atmospheric waves generated within the troposphere and dissipated within the lower thermosphere. | Thermosphere | Wikipedia | 457 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
Solar XUV radiation
The solar X-ray and extreme ultraviolet radiation (XUV) at wavelengths < 170 nm is almost completely absorbed within the thermosphere. This radiation causes the various ionospheric layers as well as a temperature increase at these heights (Figure 1).
While the solar visible light (380 to 780 nm) is nearly constant with the variability of not more than about 0.1% of the solar constant, the solar XUV radiation is highly variable in time and space. For instance, X-ray bursts associated with solar flares can dramatically increase their intensity over preflare levels by many orders of magnitude over some time of tens of minutes. In the extreme ultraviolet, the Lyman α line at 121.6 nm represents an important source of ionization and dissociation at ionospheric D layer heights. During quiet periods of solar activity, it alone contains more energy than the rest of the XUV spectrum. Quasi-periodic changes of the order of 100% or greater, with periods of 27 days and 11 years, belong to the prominent variations of solar XUV radiation. However, irregular fluctuations over all time scales are present all the time. During the low solar activity, about half of the total energy input into the thermosphere is thought to be solar XUV radiation. That solar XUV energy input occurs only during daytime conditions, maximizing at the equator during equinox. | Thermosphere | Wikipedia | 286 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
Solar wind
The second source of energy input into the thermosphere is solar wind energy which is transferred to the magnetosphere by mechanisms that are not well understood. One possible way to transfer energy is via a hydrodynamic dynamo process. Solar wind particles penetrate the polar regions of the magnetosphere where the geomagnetic field lines are essentially vertically directed. An electric field is generated, directed from dawn to dusk. Along the last closed geomagnetic field lines with their footpoints within the auroral zones, field-aligned electric currents can flow into the ionospheric dynamo region where they are closed by electric Pedersen and Hall currents. Ohmic losses of the Pedersen currents heat the lower thermosphere (see e.g., Magnetospheric electric convection field). Also, penetration of high energetic particles from the magnetosphere into the auroral regions enhance drastically the electric conductivity, further increasing the electric currents and thus Joule heating. During the quiet magnetospheric activity, the magnetosphere contributes perhaps by a quarter to the thermosphere's energy budget. This is about 250 K of the exospheric temperature in eq.(2). During the very large activity, however, this heat input can increase substantially, by a factor of four or more. That solar wind input occurs mainly in the auroral regions during both day and night.
Atmospheric waves
Two kinds of large-scale atmospheric waves within the lower atmosphere exist: internal waves with finite vertical wavelengths which can transport wave energy upward, and external waves with infinitely large wavelengths that cannot transport wave energy. Atmospheric gravity waves and most of the atmospheric tides generated within the troposphere belong to the internal waves. Their density amplitudes increase exponentially with height so that at the mesopause these waves become turbulent and their energy is dissipated (similar to breaking of ocean waves at the coast), thus contributing to the heating of the thermosphere by about 250 K in eq.(2). On the other hand, the fundamental diurnal tide labeled (1, −2) which is most efficiently excited by solar irradiance is an external wave and plays only a marginal role within the lower and middle atmosphere. However, at thermospheric altitudes, it becomes the predominant wave. It drives the electric Sq-current within the ionospheric dynamo region between about 100 and 200 km height. | Thermosphere | Wikipedia | 487 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
Heating, predominately by tidal waves, occurs mainly at lower and middle latitudes. The variability of this heating depends on the meteorological conditions within the troposphere and middle atmosphere, and may not exceed about 50%.
Dynamics
Within the thermosphere above an altitude of about , all atmospheric waves successively become external waves, and no significant vertical wave structure is visible. The atmospheric wave modes degenerate to the spherical functions Pnm with m a meridional wave number and n the zonal wave number (m = 0: zonal mean flow; m = 1: diurnal tides; m = 2: semidiurnal tides; etc.). The thermosphere becomes a damped oscillator system with low-pass filter characteristics. This means that smaller-scale waves (greater numbers of (n,m)) and higher frequencies are suppressed in favor of large-scale waves and lower frequencies. If one considers very quiet magnetospheric disturbances and a constant mean exospheric temperature (averaged over the sphere), the observed temporal and spatial distribution of the exospheric temperature distribution can be described by a sum of spheric functions:
(3)
Here, it is φ latitude, λ longitude, and t time, ωa the angular frequency of one year, ωd the angular frequency of one solar day, and τ = ωdt + λ the local time. ta = June 21 is the date of northern summer solstice, and τd = 15:00 is the local time of maximum diurnal temperature. | Thermosphere | Wikipedia | 321 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
The first term in (3) on the right is the global mean of the exospheric temperature (of the order of 1000 K). The second term [with P20 = 0.5(3 sin2(φ)−1)] represents the heat surplus at lower latitudes and a corresponding heat deficit at higher latitudes (Fig. 2a). A thermal wind system develops with the wind toward the poles in the upper level and winds away from the poles in the lower level. The coefficient ΔT20 ≈ 0.004 is small because Joule heating in the aurora regions compensates that heat surplus even during quiet magnetospheric conditions. During disturbed conditions, however, that term becomes dominant, changing sign so that now heat surplus is transported from the poles to the equator. The third term (with P10 = sin φ) represents heat surplus on the summer hemisphere and is responsible for the transport of excess heat from the summer into the winter hemisphere (Fig. 2b). Its relative amplitude is of the order ΔT10 ≃ 0.13. The fourth term (with P11(φ) = cos φ) is the dominant diurnal wave (the tidal mode (1,−2)). It is responsible for the transport of excess heat from the daytime hemisphere into the nighttime hemisphere (Fig. 2d). Its relative amplitude is ΔT11≃ 0.15, thus on the order of 150 K. Additional terms (e.g., semiannual, semidiurnal terms, and higher-order terms) must be added to eq.(3). However, they are of minor importance. Corresponding sums can be developed for density, pressure, and the various gas constituents. | Thermosphere | Wikipedia | 351 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
Thermospheric storms
In contrast to solar XUV radiation, magnetospheric disturbances, indicated on the ground by geomagnetic variations, show an unpredictable impulsive character, from short periodic disturbances of the order of hours to long-standing giant storms of several days' duration. The reaction of the thermosphere to a large magnetospheric storm is called a thermospheric storm. Since the heat input into the thermosphere occurs at high latitudes (mainly into the auroral regions), the heat transport is represented by the term P20 in eq.(3) is reversed. Also, due to the impulsive form of the disturbance, higher-order terms are generated which, however, possess short decay times and thus quickly disappear. The sum of these modes determines the "travel time" of the disturbance to the lower latitudes, and thus the response time of the thermosphere with respect to the magnetospheric disturbance. Important for the development of an ionospheric storm is the increase of the ratio N2/O during a thermospheric storm at middle and higher latitude. An increase of N2 increases the loss process of the ionospheric plasma and causes therefore a decrease of the electron density within the ionospheric F-layer (negative ionospheric storm).
Climate change
A contraction of the thermosphere has been observed as a possible result in part due to increased carbon dioxide concentrations, the strongest cooling and contraction occurring in that layer during solar minimum. The most recent contraction in 2008–2009 was the largest such since at least 1967. | Thermosphere | Wikipedia | 331 | 47463 | https://en.wikipedia.org/wiki/Thermosphere | Physical sciences | Atmosphere: General | Earth science |
In optics, the aperture of an optical system (including a system consisted of a single lens) is a hole or an opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image of the aperture and focal length of an optical system determine the cone angle of a bundle of rays that comes to a focus in the image plane.
An optical system typically has many openings or structures that limit ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that primarily determines the cone of rays that an optical system accepts (see entrance pupil). As a result, it also determines the ray cone angle and brightness at the image point (see exit pupil). The aperture stop generally depends on the object point location; on-axis object points at different object planes may have different aperture stops, and even object points at different lateral locations at the same object plane may have different aperture stops (vignetted). In practice, many object systems are designed to have a single aperture stop at designed working distance and field of view.
In some contexts, especially in photography and astronomy, aperture refers to the opening diameter of the aperture stop through which light can pass. For example, in a telescope, the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a aperture. The aperture stop is not necessarily the smallest stop in the system. Magnification and demagnification by lenses and other elements can cause a relatively large stop to be the aperture stop for the system. In astrophotography, the aperture may be given as a linear measure (for example, in inches or millimetres) or as the dimensionless ratio between that measure and the focal length. In other photography, it is usually given as a ratio.
A usual expectation is that the term aperture refers to the opening of the aperture stop, but in reality, the term aperture and the aperture stop are mixed in use. Sometimes even stops that are not the aperture stop of an optical system are also called apertures. Contexts need to clarify these terms. | Aperture | Wikipedia | 505 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
The word aperture is also used in other contexts to indicate a system which blocks off light outside a certain region. In astronomy, for example, a photometric aperture around a star usually corresponds to a circular window around the image of a star within which the light intensity is assumed.
Application | Aperture | Wikipedia | 56 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
The aperture stop is an important element in most optical designs. Its most obvious feature is that it limits the amount of light that can reach the image/film plane. This can be either unavoidable due to the practical limit of the aperture stop size, or deliberate to prevent saturation of a detector or overexposure of film. In both cases, the size of the aperture stop determines the amount of light admitted by an optical system. The aperture stop also affects other optical system properties:
The opening size of the stop is one factor that affects DOF (depth of field). A smaller stop (larger f number) produces a longer DOF because it only allows a smaller angle of the cone of light reaching the image plane so the spread of the image of an object point is reduced. A longer DOF allows objects at a wide range of distances from the viewer to all be in focus at the same time.
The stop limits the effect of optical aberrations by limiting light such that the light does not reach edges of optics where aberrations are usually stronger than the optics centers. If the opening of the stop (called the aperture) is too large, then the image will be distorted by stronger aberrations. More sophisticated optical system designs can mitigate the effect of aberrations, allowing a larger aperture and therefore greater light collecting ability.
The stop determines whether the image will be vignetted. Larger stops can cause the light intensity reaching the film or detector to fall off toward the edges of the picture, especially when, for off-axis points, a different stop becomes the aperture stop by virtue of cutting off more light than did the stop that was the aperture stop on the optic axis.
The stop location determines the telecentricity. If the aperture stop of a lens is located at the front focal plane of the lens, then it becomes image-space telecentricity, i.e., the lateral size of the image is insensitive to the image plane location. If the stop is at the back focal plane of the lens, then it becomes object-space telecentricity where the image size is insensitive to the object plane location. The telecentricity helps precise two-dimensional measurements because measurement systems with the telecentricity are insensitive to axial position errors of samples or the sensor. | Aperture | Wikipedia | 481 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
In addition to an aperture stop, a photographic lens may have one or more field stops, which limit the system's field of view. When the field of view is limited by a field stop in the lens (rather than at the film or sensor) vignetting results; this is only a problem if the resulting field of view is less than was desired.
In astronomy, the opening diameter of the aperture stop (called the aperture) is a critical parameter in the design of a telescope. Generally, one would want the aperture to be as large as possible, to collect the maximum amount of light from the distant objects being imaged. The size of the aperture is limited, however, in practice by considerations of its manufacturing cost and time and its weight, as well as prevention of aberrations (as mentioned above).
Apertures are also used in laser energy control, close aperture z-scan technique, diffractions/patterns, and beam cleaning. Laser applications include spatial filters, Q-switching, high intensity x-ray control.
In light microscopy, the word aperture may be used with reference to either the condenser (that changes the angle of light onto the specimen field), field iris (that changes the area of illumination on specimens) or possibly objective lens (forms primary images). See Optical microscope.
In photography
The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or image sensor. In combination with variation of shutter speed, the aperture size will regulate the film's or image sensor's degree of exposure to light. Typically, a fast shutter will require a larger aperture to ensure sufficient light exposure, and a slow shutter will require a smaller aperture to avoid excessive exposure.
A device called a diaphragm usually serves as the aperture stop and controls the aperture (the opening of the aperture stop). The diaphragm functions much like the iris of the eye – it controls the effective diameter of the lens opening (called pupil in the eyes). Reducing the aperture size (increasing the f-number) provides less light to sensor and also increases the depth of field (by limiting the angle of cone of image light reaching the sensor), which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. In general, the smaller the aperture (the larger the f-number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus. | Aperture | Wikipedia | 508 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter (the diameter of the entrance pupil). A lens typically has a set of marked "f-stops" that the f-number can be set to. A lower f-number denotes a greater aperture which allows more light to reach the film or image sensor. The photography term "one f-stop" refers to a factor of (approx. 1.41) change in f-number which corresponds to a change in aperture diameter, which in turn corresponds to a factor of 2 change in light intensity (by a factor 2 change in the aperture area).
Aperture priority is a semi-automatic shooting mode used in cameras. It permits the photographer to select an aperture setting and let the camera decide the shutter speed and sometimes also ISO sensitivity for the correct exposure. This is also referred to as Aperture Priority Auto Exposure, A mode, AV mode (aperture-value mode), or semi-auto mode.
Typical ranges of apertures used in photography are about – or – , covering six stops, which may be divided into wide, middle, and narrow of two stops each, roughly (using round numbers) – , – , and – or (for a slower lens) – , – , and – . These are not sharp divisions, and ranges for specific lenses vary.
Maximum and minimum apertures
The specifications for a given lens typically include the maximum and minimum aperture (opening) sizes, for example, – . In this case, is currently the maximum aperture (the widest opening on a full-frame format for practical use), and is the minimum aperture (the smallest opening). The maximum aperture tends to be of most interest and is always included when describing a lens. This value is also known as the lens "speed", as it affects the exposure time. As the aperture area is proportional to the light admitted by a lens or an optical system, the aperture diameter is proportional to the square root of the light admitted, and thus inversely proportional to the square root of required exposure time, such that an aperture of allows for exposure times one quarter that of . ( is 4 times larger than in the aperture area.) | Aperture | Wikipedia | 449 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
Lenses with apertures opening or wider are referred to as "fast" lenses, although the specific point has changed over time (for example, in the early 20th century aperture openings wider than were considered fast. The fastest lenses for the common 35 mm film format in general production have apertures of or , with more at and , and many at or slower; is unusual, though sees some use. When comparing "fast" lenses, the image format used must be considered. Lenses designed for a small format such as half frame or APS-C need to project a much smaller image circle than a lens used for large format photography. Thus the optical elements built into the lens can be far smaller and cheaper.
In exceptional circumstances lenses can have even wider apertures with f-numbers smaller than 1.0; see lens speed: fast lenses for a detailed list. For instance, both the current Leica Noctilux-M 50mm ASPH and a 1960s-era Canon 50mm rangefinder lens have a maximum aperture of . Cheaper alternatives began appearing in the early 2010s, such as the Cosina Voigtländer Nokton (several in the range) and () Super Nokton manual focus lenses in the for the Micro Four-Thirds System, and the Venus Optics (Laowa) Argus .
Professional lenses for some movie cameras have f-numbers as small as . Stanley Kubrick's film Barry Lyndon has scenes shot by candlelight with a NASA/Zeiss 50mm f/0.7, the fastest lens in film history. Beyond the expense, these lenses have limited application due to the correspondingly shallower depth of field (DOF) – the scene must either be shallow, shot from a distance, or will be significantly defocused, though this may be the desired effect.
Zoom lenses typically have a maximum relative aperture (minimum f-number) of to through their range. High-end lenses will have a constant aperture, such as or , which means that the relative aperture will stay the same throughout the zoom range. A more typical consumer zoom will have a variable maximum relative aperture since it is harder and more expensive to keep the maximum relative aperture proportional to the focal length at long focal lengths; to is an example of a common variable aperture range in a consumer zoom lens. | Aperture | Wikipedia | 466 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
By contrast, the minimum aperture does not depend on the focal length – it is limited by how narrowly the aperture closes, not the lens design – and is instead generally chosen based on practicality: very small apertures have lower sharpness due to diffraction at aperture edges, while the added depth of field is not generally useful, and thus there is generally little benefit in using such apertures. Accordingly, DSLR lens typically have minimum aperture of , , or , while large format may go down to , as reflected in the name of Group f/64. Depth of field is a significant concern in macro photography, however, and there one sees smaller apertures. For example, the Canon MP-E 65mm can have effective aperture (due to magnification) as small as . The pinhole optic for Lensbaby creative lenses has an aperture of just .
Aperture area
The amount of light captured by an optical system is proportional to the area of the entrance pupil that is the object space-side image of the aperture of the system, equal to:
Where the two equivalent forms are related via the f-number N = f / D, with focal length f and entrance pupil diameter D.
The focal length value is not required when comparing two lenses of the same focal length; a value of 1 can be used instead, and the other factors can be dropped as well, leaving area proportion to the reciprocal square of the f-number N.
If two cameras of different format sizes and focal lengths have the same angle of view, and the same aperture area, they gather the same amount of light from the scene. In that case, the relative focal-plane illuminance, however, would depend only on the f-number N, so it is less in the camera with the larger format, longer focal length, and higher f-number. This assumes both lenses have identical transmissivity.
Aperture control | Aperture | Wikipedia | 386 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
Though as early as 1933 Torkel Korling had invented and patented for the Graflex large format reflex camera an automatic aperture control, not all early 35mm single lens reflex cameras had the feature. With a small aperture, this darkened the viewfinder, making viewing, focusing, and composition difficult. Korling's design enabled full-aperture viewing for accurate focus, closing to the pre-selected aperture opening when the shutter was fired and simultaneously synchronising the firing of a flash unit. From 1956 SLR camera manufacturers separately developed automatic aperture control (the Miranda T 'Pressure Automatic Diaphragm', and other solutions on the Exakta Varex IIa and Praktica FX2) allowing viewing at the lens's maximum aperture, stopping the lens down to the working aperture at the moment of exposure, and returning the lens to maximum aperture afterward. The first SLR cameras with internal ("through-the-lens" or "TTL") meters (e.g., the Pentax Spotmatic) required that the lens be stopped down to the working aperture when taking a meter reading. Subsequent models soon incorporated mechanical coupling between the lens and the camera body, indicating the working aperture to the camera for exposure while allowing the lens to be at its maximum aperture for composition and focusing; this feature became known as open-aperture metering. | Aperture | Wikipedia | 277 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
For some lenses, including a few long telephotos, lenses mounted on bellows, and perspective-control and tilt/shift lenses, the mechanical linkage was impractical, and automatic aperture control was not provided. Many such lenses incorporated a feature known as a "preset" aperture, which allows the lens to be set to working aperture and then quickly switched between working aperture and full aperture without looking at the aperture control. A typical operation might be to establish rough composition, set the working aperture for metering, return to full aperture for a final check of focus and composition, and focusing, and finally, return to working aperture just before exposure. Although slightly easier than stopped-down metering, operation is less convenient than automatic operation. Preset aperture controls have taken several forms; the most common has been the use of essentially two lens aperture rings, with one ring setting the aperture and the other serving as a limit stop when switching to working aperture. Examples of lenses with this type of preset aperture control are the Nikon PC Nikkor 28 mm and the SMC Pentax Shift 6×7 75 mm . The Nikon PC Micro-Nikkor 85 mm lens incorporates a mechanical pushbutton that sets working aperture when pressed and restores full aperture when pressed a second time.
Canon EF lenses, introduced in 1987, have electromagnetic diaphragms, eliminating the need for a mechanical linkage between the camera and the lens, and allowing automatic aperture control with the Canon TS-E tilt/shift lenses. Nikon PC-E perspective-control lenses, introduced in 2008, also have electromagnetic diaphragms, a feature extended to their E-type range in 2013.
Optimal aperture
Optimal aperture depends both on optics (the depth of the scene versus diffraction), and on the performance of the lens.
Optically, as a lens is stopped down, the defocus blur at the Depth of Field (DOF) limits decreases but diffraction blur increases. The presence of these two opposing factors implies a point at which the combined blur spot is minimized (Gibson 1975, 64); at that point, the f-number is optimal for image sharpness, for this given depth of field – a wider aperture (lower f-number) causes more defocus, while a narrower aperture (higher f-number) causes more diffraction. | Aperture | Wikipedia | 483 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
As a matter of performance, lenses often do not perform optimally when fully opened, and thus generally have better sharpness when stopped down some – this is sharpness in the plane of critical focus, setting aside issues of depth of field. Beyond a certain point, there is no further sharpness benefit to stopping down, and the diffraction occurred at the edges of the aperture begins to become significant for imaging quality. There is accordingly a sweet spot, generally in the – range, depending on lens, where sharpness is optimal, though some lenses are designed to perform optimally when wide open. How significant this varies between lenses, and opinions differ on how much practical impact this has.
While optimal aperture can be determined mechanically, how much sharpness is required depends on how the image will be used – if the final image is viewed under normal conditions (e.g., an 8″×10″ image viewed at 10″), it may suffice to determine the f-number using criteria for minimum required sharpness, and there may be no practical benefit from further reducing the size of the blur spot. But this may not be true if the final image is viewed under more demanding conditions, e.g., a very large final image viewed at normal distance, or a portion of an image enlarged to normal size (Hansma 1996). Hansma also suggests that the final-image size may not be known when a photograph is taken, and obtaining the maximum practicable sharpness allows the decision to make a large final image to be made at a later time; see also critical sharpness.
In biology | Aperture | Wikipedia | 327 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
In many living optical systems, the eye consists of an iris which adjusts the size of the pupil, through which light enters. The iris is analogous to the diaphragm, and the pupil (which is the adjustable opening in the iris) the aperture. Refraction in the cornea causes the effective aperture (the entrance pupil in optics parlance) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it can range from as narrow as 2 mm () in diameter in a brightly lit place to 8 mm () in the dark as part of adaptation. In rare cases in some individuals are able to dilate their pupils even beyond 8 mm (in scotopic lighting, close to the physical limit of the iris. In humans, the average iris diameter is about 11.5 mm, which naturally influences the maximal size of the pupil as well, where larger iris diameters would typically have pupils which are able to dilate to a wider extreme than those with smaller irises. Maximum dilated pupil size also decreases with age.
The iris controls the size of the pupil via two complementary sets muscles, the sphincter and dilator muscles, which are innervated by the parasympathetic and sympathetic nervous systems respectively, and act to induce pupillary constriction and dilation respectively. The state of the pupil is closely influenced by various factors, primarily light (or absence of light), but also by emotional state, interest in the subject of attention, arousal, sexual stimulation, physical activity, accommodation state, and cognitive load. The field of view is not affected by the size of the pupil.
Some individuals are also able to directly exert manual and conscious control over their iris muscles and hence are able to voluntarily constrict and dilate their pupils on command. However, this ability is rare and potential use or advantages are unclear.
Equivalent aperture range | Aperture | Wikipedia | 390 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
In digital photography, the 35mm-equivalent aperture range is sometimes considered to be more important than the actual f-number. Equivalent aperture is the f-number adjusted to correspond to the f-number of the same size absolute aperture diameter on a lens with a 35mm equivalent focal length. Smaller equivalent f-numbers are expected to lead to higher image quality based on more total light from the subject, as well as lead to reduced depth of field. For example, a Sony Cyber-shot DSC-RX10 uses a 1" sensor, 24 – 200 mm with maximum aperture constant along the zoom range; has equivalent aperture range , which is a lower equivalent f-number than some other cameras with smaller sensors.
However, modern optical research concludes that sensor size does not actually play a part in the depth of field in an image. An aperture's f-number is not modified by the camera's sensor size because it is a ratio that only pertains to the attributes of the lens. Instead, the higher crop factor that comes as a result of a smaller sensor size means that, in order to get an equal framing of the subject, the photo must be taken from further away, which results in a less blurry background, changing the perceived depth of field. Similarly, a smaller sensor size with an equivalent aperture will result in a darker image because of the pixel density of smaller sensors with equivalent megapixels. Every photosite on a camera's sensor requires a certain amount of surface area that is not sensitive to light, a factor that results in differences in pixel pitch and changes in the signal-noise ratio. However, neither the changed depth of field, nor the perceived change in light sensitivity are a result of the aperture. Instead, equivalent aperture can be seen as a rule of thumb to judge how changes in sensor size might affect an image, even if qualities like pixel density and distance from the subject are the actual causes of changes in the image.
In scanning or sampling
The terms scanning aperture and sampling aperture are often used to refer to the opening through which an image is sampled, or scanned, for example in a Drum scanner, an image sensor, or a television pickup apparatus. The sampling aperture can be a literal optical aperture, that is, a small opening in space, or it can be a time-domain aperture for sampling a signal waveform.
For example, film grain is quantified as graininess via a measurement of film density fluctuations as seen through a 0.048 mm sampling aperture.
In popular culture | Aperture | Wikipedia | 512 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
Aperture Science, a fictional company in the Portal fictional universe, is named after the optical system. The company's logo heavily features an aperture in its logo, and has come to symbolize the series, fictional company, and the Aperture Science Laboratories Computer-Aided Enrichment Center that the game series takes place in. | Aperture | Wikipedia | 62 | 47474 | https://en.wikipedia.org/wiki/Aperture | Physical sciences | Optics | Physics |
An aquifer is an underground layer of water-bearing material, consisting of permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude (or aquifuge), which is a solid, impermeable area underlying or overlying an aquifer, the pressure of which could lead to the formation of a confined aquifer. The classification of aquifers is as follows: Saturated versus unsaturated; aquifers versus aquitards; confined versus unconfined; isotropic versus anisotropic; porous, karst, or fractured; transboundary aquifer.
Groundwater from aquifers can be sustainably harvested by humans through the use of qanats leading to a well. This groundwater is a major source of fresh water for many regions, however can present a number of challenges such as overdrafting (extracting groundwater beyond the equilibrium yield of the aquifer), groundwater-related subsidence of land, and the salinization or pollution of the groundwater.
Properties
Depth
Aquifers occur from near-surface to deeper than . Those closer to the surface are not only more likely to be used for water supply and irrigation, but are also more likely to be replenished by local rainfall. Although aquifers are sometimes characterized as "underground rivers or lakes," they are actually porous rock saturated with water.
Many desert areas have limestone hills or mountains within them or close to them that can be exploited as groundwater resources. Part of the Atlas Mountains in North Africa, the Lebanon and Anti-Lebanon ranges between Syria and Lebanon, the Jebel Akhdar in Oman, parts of the Sierra Nevada and neighboring ranges in the United States' Southwest, have shallow aquifers that are exploited for their water. Overexploitation can lead to the exceeding of the practical sustained yield; i.e., more water is taken out than can be replenished.
Along the coastlines of certain countries, such as Libya and Israel, increased water usage associated with population growth has caused a lowering of the water table and the subsequent contamination of the groundwater with saltwater from the sea. | Aquifer | Wikipedia | 512 | 47481 | https://en.wikipedia.org/wiki/Aquifer | Physical sciences | Hydrology | Earth science |
In 2013 large freshwater aquifers were discovered under continental shelves off Australia, China, North America and South Africa. They contain an estimated half a million cubic kilometers of "low salinity" water that could be economically processed into potable water. The reserves formed when ocean levels were lower and rainwater made its way into the ground in land areas that were not submerged until the ice age ended 20,000 years ago. The volume is estimated to be 100 times the amount of water extracted from other aquifers since 1900.
Groundwater recharge
Classification
An aquitard is a zone within the Earth that restricts the flow of groundwater from one aquifer to another. An aquitard can sometimes, if completely impermeable, be called an aquiclude or aquifuge. Aquitards are composed of layers of either clay or non-porous rock with low hydraulic conductivity.
Saturated versus unsaturated
Groundwater can be found at nearly every point in the Earth's shallow subsurface to some degree, although aquifers do not necessarily contain fresh water. The Earth's crust can be divided into two regions: the saturated zone or phreatic zone (e.g., aquifers, aquitards, etc.), where all available spaces are filled with water, and the unsaturated zone (also called the vadose zone), where there are still pockets of air that contain some water, but can be filled with more water.
Saturated means the pressure head of the water is greater than atmospheric pressure (it has a gauge pressure > 0). The definition of the water table is the surface where the pressure head is equal to atmospheric pressure (where gauge pressure = 0). | Aquifer | Wikipedia | 360 | 47481 | https://en.wikipedia.org/wiki/Aquifer | Physical sciences | Hydrology | Earth science |
Unsaturated conditions occur above the water table where the pressure head is negative (absolute pressure can never be negative, but gauge pressure can) and the water that incompletely fills the pores of the aquifer material is under suction. The water content in the unsaturated zone is held in place by surface adhesive forces and it rises above the water table (the zero-gauge-pressure isobar) by capillary action to saturate a small zone above the phreatic surface (the capillary fringe) at less than atmospheric pressure. This is termed tension saturation and is not the same as saturation on a water-content basis. Water content in a capillary fringe decreases with increasing distance from the phreatic surface. The capillary head depends on soil pore size. In sandy soils with larger pores, the head will be less than in clay soils with very small pores. The normal capillary rise in a clayey soil is less than but can range between .
The capillary rise of water in a small-diameter tube involves the same physical process. The water table is the level to which water will rise in a large-diameter pipe (e.g., a well) that goes down into the aquifer and is open to the atmosphere.
Aquifers versus aquitards
Aquifers are typically saturated regions of the subsurface that produce an economically feasible quantity of water to a well or spring (e.g., sand and gravel or fractured bedrock often make good aquifer materials).
An aquitard is a zone within the Earth that restricts the flow of groundwater from one aquifer to another. A completely impermeable aquitard is called an aquiclude or aquifuge. Aquitards contain layers of either clay or non-porous rock with low hydraulic conductivity. | Aquifer | Wikipedia | 395 | 47481 | https://en.wikipedia.org/wiki/Aquifer | Physical sciences | Hydrology | Earth science |
In mountainous areas (or near rivers in mountainous areas), the main aquifers are typically unconsolidated alluvium, composed of mostly horizontal layers of materials deposited by water processes (rivers and streams), which in cross-section (looking at a two-dimensional slice of the aquifer) appear to be layers of alternating coarse and fine materials. Coarse materials, because of the high energy needed to move them, tend to be found nearer the source (mountain fronts or rivers), whereas the fine-grained material will make it farther from the source (to the flatter parts of the basin or overbank areas—sometimes called the pressure area). Since there are less fine-grained deposits near the source, this is a place where aquifers are often unconfined (sometimes called the forebay area), or in hydraulic communication with the land surface.
Confined versus unconfined
An unconfined aquifer has no impermeable barrier immediately above it, such that the water level can rise in response to recharge. A confined aquifer has an overlying impermeable barrier that prevents the water level in the aquifer from rising any higher. An aquifer in the same geologic unit may be confined in one area and unconfined in another. Unconfined aquifers are sometimes also called water table or phreatic aquifers, because their upper boundary is the water table or phreatic surface (see Biscayne Aquifer). Typically (but not always) the shallowest aquifer at a given location is unconfined, meaning it does not have a confining layer (an aquitard or aquiclude) between it and the surface. The term "perched" refers to ground water accumulating above a low-permeability unit or strata, such as a clay layer. This term is generally used to refer to a small local area of ground water that occurs at an elevation higher than a regionally extensive aquifer. The difference between perched and unconfined aquifers is their size (perched is smaller). Confined aquifers are aquifers that are overlain by a confining layer, often made up of clay. The confining layer might offer some protection from surface contamination. | Aquifer | Wikipedia | 486 | 47481 | https://en.wikipedia.org/wiki/Aquifer | Physical sciences | Hydrology | Earth science |
If the distinction between confined and unconfined is not clear geologically (i.e., if it is not known if a clear confining layer exists, or if the geology is more complex, e.g., a fractured bedrock aquifer), the value of storativity returned from an aquifer test can be used to determine it (although aquifer tests in unconfined aquifers should be interpreted differently than confined ones). Confined aquifers have very low storativity values (much less than 0.01, and as little as ), which means that the aquifer is storing water using the mechanisms of aquifer matrix expansion and the compressibility of water, which typically are both quite small quantities. Unconfined aquifers have storativities (typically called specific yield) greater than 0.01 (1% of bulk volume); they release water from storage by the mechanism of actually draining the pores of the aquifer, releasing relatively large amounts of water (up to the drainable porosity of the aquifer material, or the minimum volumetric water content).
Isotropic versus anisotropic
In isotropic aquifers or aquifer layers the hydraulic conductivity (K) is equal for flow in all directions, while in anisotropic conditions it differs, notably in horizontal (Kh) and vertical (Kv) sense.
Semi-confined aquifers with one or more aquitards work as an anisotropic system, even when the separate layers are isotropic, because the compound Kh and Kv values are different (see hydraulic transmissivity and hydraulic resistance).
When calculating flow to drains or flow to wells in an aquifer, the anisotropy is to be taken into account lest the resulting design of the drainage system may be faulty.
Porous, karst, or fractured | Aquifer | Wikipedia | 401 | 47481 | https://en.wikipedia.org/wiki/Aquifer | Physical sciences | Hydrology | Earth science |
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