International Earth Rotation Service

The Sub-bureau for Rapid Service and Predictions of Earth Orientation Parameters of the IERS, located at the United States Naval Observatory, monitors the Earth's rotation. Part of its mission involves the determination of a time scale based on the current rate of the rotation of the Earth. UT1 is the non-uniform time based on the Earth's rotation.

External references:

• IERS site: http://www.iers.org
• IERS Bulletin, where leap seconds are announced: http://www.iers.org/iers/publications/bulletins/bull_c/
• IERS Archive, to view old announcements: http://www.iers.org/iers/earth/rotation/utc/table2
• Public domain article on leap seconds (http://tycho.usno.navy.mil/leapsec)