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Earth Orientation Department

The U.S. Naval Observatory's Earth Orientation Department is responsible for determining and predicting the time-varying alignment of the Earth's terrestrial reference frame with respect to the celestial reference frame, commonly referred to as Earth Orientation Parameters (EOPs).  USNO is the International Earth Rotation and Reference Systems Service (IERS) Rapid Service/Prediction Center (RS/PC) for Earth Orientation.
EOPs are derived from a number of different sources.  The most precise parameters are determined by a network of radio telescopes that work together in a technique called Very Long Baseline Interferometry, or VLBI.  USNO maintains a VLBI station at Kokee Park, Kauai, Hawai'i and collaborates with many other radio observatories to observe quasars and Active Galactic Nuclei (AGNs).  These objects are the super-massive black holes that reside in the centers of extremely distant galaxies billions of light-years away.  By observing the same object at the same time with several of these radio telescopes we can measure the precise location of the object on the plane of the sky and also measure the precise location of each telescope on the ground.  Data from these diverse telescopes is sent to USNO via dedicated Internet connections or on physical media where it is processed on a dedicated computer system, the VLBI Correlator.  EOPs are updated daily for distribution by the IERS.

Earth Orientation Products

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


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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