ephemeris

ephemeris (pl., ephemerides), table listing the position of one or more celestial bodies for each day of the year. The French publication Connaissance de Temps is the oldest of the national astronomical ephemerides, founded in 1679. The Nautical Almanac and Astronomical Ephemeris (usually abbreviated to the Nautical Almanac ), an annual publication by the British Royal Observatory at Greenwich since 1767, has been a leading compilation of ephemerides since its inception. Its original purpose was to provide the astronomical information necessary to derive longitude at sea. In 1852 the U.S. Naval Observatory began publishing a book called the American Ephemeris and Nautical Almanac, which contained similar information to that published at Greenwich but adjusted for the meridian at Washington, D.C. Beginning with the edition for 1958, Great Britain and the United States, in a joint effort, issued ephemerides that are identical in content, although they remain separate publications with different names (the British volume was renamed The Astronomical Ephemeris ); in 1981 the British and American publications were combined as The Astronomical Almanac. This ephemeris (adapted to the Greenwich meridian) is issued well in advance of the dates covered and contains such information as the daily right ascension and declination of the sun, moon, planets, and other celestial bodies, and daily data on the sunrise, sunset, moonrise, and moonset. Among other publications issued are The Ephemeris (U.S.) and The Star Almanac for Land Surveyors (Brit.), which are star ephemerides used by surveyors, and the Air Almanac (Brit./U.S.), used in air navigation. By international agreement the basic calculations of astronomical ephemerides are shared among a number of countries including France, Germany, Spain, and Russia. The Ephemerides of Minor Planets is compiled and published annually by the Institute of Theoretical Astronomy, St. Petersburg (formerly Leningrad). In addition, the International Astronomical Union issues ephemerides for every newly discovered comet and for many newly found asteroids. Through the Minor Planet Center in Cambridge, Mass., astronomers can obtain ephemerides of any asteroid or comet.

ephemeris A table giving the predicted positions of a celestial object at given times; pl.ephemerides. Collections of ephemerides for various objects are published in yearly almanacs, such as The Astronomical Almanac.