The Earth Orientation Department of the U.S. Naval Observatory determines and predicts the time-varying alignment of the Earth's terrestrial reference frame with respect to the celestial reference frame. The Earth Orientation Parameters (EOP) determined are the coordinates of the Earth's pole (polar motion), the rotation angle about the pole (Universal Time or UT1), precession, and nutation. The Earth Orientation Department also determines and maintains the positions of the extragalactic radio sources which form the basis for the quasi-inertial celestial reference frame within which the EOP parameters are determined. To accomplish it's mission, the department conducts operations and research in the following areas:

• Earth Orientation Parameters (EOP) analysis and prediction;
• Global Positioning System (GPS) data analysis;
• the Radio Reference Frame; and
• Very Long Baseline Interferometry (VLBI) data analysis.

The VLBI data are correlated and analyzed at the Washington Correlator (WACO), which is operated and maintained by the Earth Orientation Department, in close cooperation with the VLBI Group of the National Aeronautics and Space Administration's Space Geodesy Program. The WACO is located in Washington, D.C. on the grounds of the U.S. Naval Observatory.