NOTICE TO USERS
Commander, Naval Meteorology and Oceanography Command is consolidating the command's web presence in accordance with Department of Defense (DoD) and Navy guidance. The U.S. Naval Oceanography portal will be the single access point for all public facing Meteorology and Oceanography products and services. This publicly-accessible portal is currently online at http://www.usno.navy.mil and is being populated. In the near future, non-DoD users will be redirected to this portal.
DoD customers can access all operational data, products and services via the NIPRnet Naval Oceanography Portal site at https://oceanography.navy.mil (CAC required).
Terrestrial Time (TT) is a time scale established by the International Astronomical Union (IAU) to serve as the independent argument for apparent geocentric ephemerides. That is, TT is used for the prediction or recording of the positions of celestial bodies as measured by an observer on Earth. It is the successor to Ephemeris Time (ET), but is based on the SI second.
Terrestrial Time is effectively equal to International Atomic Time (TAI) plus 32.184 seconds exactly.
The epoch designated "J2000.0" is specified as Julian date 2451545.0 TT, or 2000 January 1, 12h TT. This epoch can also be expressed as 2000 January 1, 11:59:27.816 TAI or 2000 January 1, 11:58:55.816 UTC.
