U.S. Naval Observatory Earth Orientation Department

Data Products

  • IERS Bulletin A (The National Earth Orientation Service Bulletin)
  • The Bulletin A Web Page
  • The most recent Earth Orientation Parameters (x, y, and UT1-UTC)
  • The Radio Optical Reference Frame (RORF)
  • The Radio Reference Frame Image Database (RRFID)
  • The Optical Image Database (OID)
  • Obtaining NEOS VLBI data
  • The Explanatory Supplement to IERS Bulletins A and B
  • Historical differences between International Atomic Time (TAI) and Coordinated Universal Time (UTC)
  • What is Earth Orientation?
  • What is a leap second?
  • Would you like to regularly receive EOP data? If so, please fill out and submit a product request form (requires a 'forms' capable browser).


  • 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 Washington Correlator (WACO)


  • United States Naval Observatory (USNO)
  • International Astronomical Union (IAU)
  • International Earth Rotation Service (IERS)
  • International VLBI Service (IVS)
  • VLBI Group of NASA's Space Geodesy Program
  • International GPS Service (IGS)
  • Home [Data Products] [Programs] [Publications] [FAQ] [Site Index]

    Last modified: 29 July 2009 Approved by EO Dept. Head, USNO