Greenwich Time Zone
Monthly Ephemeris (Links on the Right)
A list of computed positions occupied by a celestial body over successive intervals of time.
(-Matrix Software, Astro*Index)
pl. Ephemerides. An almanac listing the ephemeral or rapidly changing position which each of the solar system bodies will occupy on each day of the year: their Longitude, Latitude, Declination, and similar astronomical phenomena. The astronomer's Ephemeris lists these positions in heliocentric terms; that of the astrologer, in geocentric terms. A set of Ephemerides which includes the year of the native's birth, is essential in the erection of a horoscope. Ephemerides were first devised by astrologers to facilitate the erection of a horoscope. Finally, when they became of common use to navigators and astronomers, they were given official recognition by the Government, and issued as the Nautical Almanac. The oldest almanac in the British Museum bears the date 143I. It is said that Columbus navigated by the aid of an Astrologer's Ephemeris.
Some of the notable ephemerides have been: Vincent Wing, 1658-81; John Gadbury, 1682-1702; Edmund Weaver, 1740-46; Thomas White, 1762-1850 (also reappeared in 1883); George Parker, in Celestial Atlas, 1780-90; John Partridge, in Merlinus Liberatus, 1851-59; E. W. Williams, in the Celestial Messenger, 1858; W. J. Simmonite, 1801-61; Raphael, 1820 to date.
The old astronomical day which began at noon was abolished on Jan. 1, 1925, and since then the astronomical day has begun at midnight. Gradually this is reflected in the making of Ephemerides. Therefore it is important to verify whether the ephemeris one is using for any given year since around 1930 shows the planets' places at noon or midnight. This can be determined at a glance by noting the sidereal time on Jan. 1: if it is around 18h the ephemeris is for noon; if around 6h, it is for midnight; if neither of these, it is probably calculated for some longitude other than that of Greenwich.
(-Nicholas de Vore's Encyclopedia of Astrology)