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Earth Orientation

The U.S. Naval Observatory is responsible for determining and predicting the time-varying alignment of the Earth's terrestrial reference frame with respect to the celestial reference frame.  USNO is the International Earth Rotation and Reference Systems Service (IERS) Rapid Service/Prediction Center (RS/PC) for Earth Orientation.

Earth Orientation Products

The latest determinations and predictions for polar motion, UT1-UTC, celestial pole offsets, and long-term Delta T are provided.

GPS-based Products

The latest 24-hour and 48-hour sets of GPS satellite orbits, satellite and receiver clock solutions, earth orientation parameters, and UTGPS (GPS-based UT1-like quantity).

VLBI-based Products

The latest Earth Orientation Parameters derived from Very Long Baseline Interferometry (VLBI) observations and correlator data products.

EO Information Center

Information regarding commonly used variables (General Information), Information for GPS Users (GPS User Information), frequently asked questions about Earth Orientation, and format descriptions for data sets (Read Me files). 

Publications about Products

Publications providing background material (Explanatory Supplement), documentation of procedures and quality of results (Annual Reports), and technical details regarding the procedures (Scientific Publications).


Supporting software for searching through Earth orientation results and for calculating the rotation matrices between terrestrial and celestial reference frames.  Recommended support and auxiliary software for use with Earth Orientation products as input.

USNO Master Clock Time
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