---
license: cc-by-4.0
pretty_name: "ICRF3 Celestial Reference Frame"
language:
  - en
description: "The third International Celestial Reference Frame (ICRF3) — the fundamental coordinate reference frame for astronomy, defined by extragalactic radio sources observed by VLBI."
task_categories:
  - tabular-classification
tags:
  - space
  - icrf
  - reference-frame
  - astrometry
  - quasar
  - vlbi
  - open-data
size_categories:
  - 1K<n<10K
---

# ICRF3 Celestial Reference Frame

The third International Celestial Reference Frame (ICRF3) is **the** fundamental coordinate
reference frame for astronomy, adopted by the International Astronomical Union in 2018.
It is defined by **4,588** extragalactic radio sources (primarily quasars) observed by
Very Long Baseline Interferometry (VLBI). This dataset contains **3,417** sources
with variability and structure parameters from the defining catalog.

## Dataset description

The ICRF is the realization of the International Celestial Reference System (ICRS) at
radio wavelengths. ICRF3 is based on nearly 40 years of VLBI observations and provides
the most accurate positions of extragalactic objects, with median positional uncertainties
of ~30 microarcseconds for the defining sources. These sources serve as the fixed reference
points against which all other celestial positions are measured.

## Schema

| Column | Type | Description |
|--------|------|-------------|
| `iers_name` | string | IERS designation of the source |
| `ra_deg` | float64 | Right ascension (degrees, ICRS) |
| `dec_deg` | float64 | Declination (degrees, ICRS) |

Additional columns from the catalog are included with snake_case names.

## Quick stats

- **3,417** ICRF3 sources

## Usage

```python
from datasets import load_dataset

ds = load_dataset("juliensimon/icrf3-reference-frame", split="train")
df = ds.to_pandas()

# All-sky distribution
print(f"{len(df):,} ICRF3 reference sources")
print(f"RA range: {df['ra_deg'].min():.2f} to {df['ra_deg'].max():.2f} deg")
print(f"Dec range: {df['dec_deg'].min():.2f} to {df['dec_deg'].max():.2f} deg")
```

## Data source

Xu, M.H., Anderson, J.M., Heinkelmann, R., et al. (2019), "Structure Effects for
3417 Celestial Reference Frame Radio Sources", ApJS, 242, 5.
Accessed via [VizieR](https://vizier.cds.unistra.fr/), CDS Strasbourg.

## Related datasets

- [pulsar-catalog](https://huggingface.co/datasets/juliensimon/pulsar-catalog) -- ATNF Pulsar Catalogue
- [open-star-clusters](https://huggingface.co/datasets/juliensimon/open-star-clusters) -- Open Star Clusters

## Pipeline

Source code: [juliensimon/space-datasets](https://github.com/juliensimon/space-datasets)

## Citation

```bibtex
@dataset{icrf3_reference_frame,
  author = {Simon, Julien},
  title = {ICRF3 Celestial Reference Frame},
  year = {2026},
  publisher = {Hugging Face},
  url = {https://huggingface.co/datasets/juliensimon/icrf3-reference-frame},
  note = {Based on Xu et al. (2019), ApJS, 242, 5 via VizieR CDS Strasbourg}
}
```

## License

[CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/)