juliensimon/iers-earth-orientation

IERS Earth Orientation Parameters

Credit: NASA

Part of a dataset collection on Hugging Face.

Dataset description

Earth Orientation Parameters (EOP) from the IERS finals2000A series. Includes polar motion, UT1-UTC, length of day, and nutation offsets. Updated daily.

Earth Orientation Parameters 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, GPS/GNSS positioning, telescope and antenna tracking, deep-space navigation, and geodesy.

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.

This dataset is suitable for tabular regression tasks.

Schema

Column	Type	Description	Sample	Null %
mjd	int64	Modified Julian Date = Julian Date - 2400000.5; a compact decimal day count used throughout astronomy and geodesy; J2000.0 corresponds to MJD 51544.5; enables direct arithmetic on time differences without calendar conversions	48622	0.0%
x_pole_arcsec	float64	x-component of polar motion in arcseconds; eastward offset of Earth's instantaneous rotation pole from the IERS Reference Pole along the Greenwich meridian; typical range +/-0.5 arcsec; a 1 mas error causes ~3 cm surface positioning error	0.182987	0.4%
sigma_x_pole_arcsec	float64	1-sigma formal uncertainty on x_pole_arcsec; reflects quality of the combined VLBI/SLR/GPS solution; typically 0.01-0.1 mas for modern observations	0.000672	0.4%
y_pole_arcsec	float64	y-component of polar motion in arcseconds; offset of Earth's rotation pole along the 90 deg W meridian; required together with x_pole_arcsec to transform between celestial (ICRF) and terrestrial (ITRF) coordinate frames	0.168775	0.4%
sigma_y_pole_arcsec	float64	1-sigma formal uncertainty on y_pole_arcsec; same origin and magnitude as sigma_x_pole_arcsec	0.000345	0.4%
ut1_utc_sec	float64	Difference UT1 - UTC in seconds; UT1 tracks Earth's actual rotational angle while UTC uses fixed SI seconds; bounded to +/-0.9 s by periodic leap-second insertions; essential for sidereal time and spacecraft antenna pointing calculations	-0.1251659	0.4%
sigma_ut1_utc_sec	float64	1-sigma formal uncertainty on ut1_utc_sec; typically sub-millisecond for recent observations	2.07e-05	0.4%
lod_ms	float64	Excess length of day above 86400 SI seconds, in milliseconds; positive = Earth rotating slower than nominal; reflects the instantaneous time derivative of UT1-UTC; driven mainly by atmospheric angular momentum exchange on sub-annual timescales	1.8335	3.3%
dx_mas	float64	Celestial pole offset dX in milliarcseconds; observed deviation of the celestial intermediate pole from the IAU 2000/2006 precession-nutation model along the X axis; corrects for unpredictable fluid-core free nutation with ~430-day period	-0.086	2.6%
dy_mas	float64	Celestial pole offset dY in milliarcseconds; observed deviation along the Y axis complementing dX; together dX and dY provide the residual nutation corrections needed for the highest-precision celestial mechanics and VLBI analysis	0.13	2.6%
date	datetime64[us]	Calendar date in UTC of the EOP measurement; daily cadence from 1962-01-01 to present; values after the last bulletin date are IERS short-term predictions, not observations	1992-01-01 00:00:00	0.0%

Quick stats

• 12,983 daily records (1992-01-01 to 2027-07-18)
• UT1-UTC range (since 2020): -0.2562 to 0.0948 s

Usage

from datasets import load_dataset

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

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

https://www.iers.org/

Update schedule

Daily at 13:00 UTC via GitHub Actions.

If you find this dataset useful, please consider giving it a like on Hugging Face. It helps others discover it.

About the author

Created by Julien Simon — AI Operating Partner at Fortino Capital. Part of the Space Datasets collection.

Citation

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

License

CC-BY-4.0