AbstractThe U.S. Naval Observatory Navnet program monitors changes in the rotation of the Earth on a regular basis using radio interferometric observations acquired with telescopes in Alaska, Hawaii, Florida, West Virginia and, in the past, Maryland; other radio telescopes have also participated occasionally. These observations have been used to derive a radio interferometric celestial reference system, Navy 1990-5, using two years of dual frequency measurements from 24-hour-duration observing sessions. A total of 84 extragalactic radio sources, mostly quasars, have been observed by the Navnet program to date, of which 70 currently have source position formal errors of one milli second of arc or less. The root mean square of the difference between source position estimates from the Navnet data and an independently derived catalog using completely different data is less than one milli second of arc in both right ascension and declination after the adjustment of an arbitrary rotational offset between the two celestial reference frames.
Time and frequency activities at the U.S. naval observatory
