juliensimon/iers-earth-orientation

IERS Earth Orientation Parameters

Part of the Space Weather Datasets collection on Hugging Face.

Earth Orientation Parameters from the IERS finals2000A series, spanning 1992-01-01 to 2027-05-30. Currently 12,934 daily records.

Dataset description

Earth Orientation Parameters (EOP) describe the irregularities in Earth's rotation and the motion of its poles. These parameters are essential for transforming between celestial and terrestrial reference frames, which is critical for:

• Satellite operations: precise orbit determination and manoeuvre planning
• GPS/GNSS: sub-centimetre positioning requires accurate UT1-UTC and polar motion
• Precise pointing: telescope and antenna tracking, deep-space navigation
• Geodesy: monitoring Earth's rotation rate, polar wander, and length of day

The IERS finals2000A series combines observed values (from VLBI, SLR, GPS) with predictions extending ~1 year into the future.

Earth's rotation is not uniform. The planet's spin axis wanders relative to both the crust (polar motion) and the celestial reference frame (precession and nutation), while the rotation rate itself fluctuates on timescales from hours to millennia. Polar motion consists of two main components: the Chandler wobble (a free oscillation with a period of approximately 433 days and amplitude of 0.1-0.2 arcseconds, equivalent to 3-6 meters at the pole) and an annual oscillation driven by seasonal redistribution of atmospheric and oceanic mass. Superimposed on these is a secular drift of the pole toward roughly 80 degrees W longitude at about 10 cm/year, driven by post-glacial rebound of the mantle.

The UT1-UTC difference tracks the accumulated departure of Earth's rotational angle from atomic time. Earth's rotation is gradually slowing due to tidal dissipation (primarily lunar tides in the oceans), causing UT1 to drift behind UTC at an average rate of roughly 2 milliseconds per day. This secular trend is punctuated by irregular decadal fluctuations attributed to core-mantle coupling, and by shorter-period variations from atmospheric angular momentum exchange. When |UT1-UTC| approaches 0.9 seconds, the IERS directs the insertion of a leap second. The length-of-day (LOD) excess, also provided in this dataset, is the time derivative of UT1-UTC and directly reflects these torques.

These parameters are not merely of academic interest -- they are operationally critical. A 1-milliarcsecond error in polar motion corresponds to roughly 3 cm of positioning error on Earth's surface, which propagates directly into satellite orbit determination, GNSS navigation solutions, and synthetic aperture radar interferometry. Deep-space missions require UT1-UTC to millimetre-equivalent accuracy for precise antenna pointing and Doppler tracking. The nutation offsets (dX, dY) correct the IAU 2000A precession-nutation model for the unpredictable influence of the fluid core's free core nutation, with a period near 430 days and amplitudes of order 0.1-0.3 milliarcseconds.

Schema

Column	Type	Description
date	datetime	Calendar date (UTC)
mjd	float64	Modified Julian Date
x_pole_arcsec	float64	Pole coordinate x (arcseconds)
y_pole_arcsec	float64	Pole coordinate y (arcseconds)
ut1_utc_sec	float64	UT1-UTC difference (seconds)
lod_ms	float64	Length of Day excess (milliseconds)
dx_mas	float64	Celestial pole offset dX (milliarcseconds)
dy_mas	float64	Celestial pole offset dY (milliarcseconds)

Quick stats

• 12,934 daily records (1992-01-01 to 2027-05-30)

Usage

from datasets import load_dataset

ds = load_dataset("juliensimon/iers-earth-orientation", split="train")
df = ds.to_pandas()

# Recent UT1-UTC values
recent = df[df["date"] > "2025-01-01"].sort_values("date")
print(recent[["date", "ut1_utc_sec", "x_pole_arcsec", "y_pole_arcsec"]])

# Polar motion scatter plot
import matplotlib.pyplot as plt
fig, ax = plt.subplots(figsize=(8, 8))
ax.scatter(df["x_pole_arcsec"], df["y_pole_arcsec"], s=0.5, alpha=0.3)
ax.set_xlabel("x pole (arcsec)")
ax.set_ylabel("y pole (arcsec)")
ax.set_title("Polar Motion")
plt.show()

Data source

International Earth Rotation and Reference Systems Service (IERS) finals2000A data series from the IERS Earth Orientation Centre.

Update schedule

Daily at 13:00 UTC via GitHub Actions.

Pipeline

Source code: juliensimon/space-datasets

Support

If you find this dataset useful, please give it a ❤️ on the dataset page and share feedback in the Community tab! Also consider giving a ⭐️ to the space-datasets repo.

Citation

@dataset{iers_earth_orientation,
  author = {Simon, Julien},
  title = {IERS Earth Orientation Parameters},
  year = {2026},
  publisher = {Hugging Face},
  url = {https://huggingface.co/datasets/juliensimon/iers-earth-orientation},
  note = {Based on IERS finals2000A Earth Orientation Parameters}
}

License

CC-BY-4.0