Ephemeris

An ephemeris is a table of the computed positions of celestial bodies against time. For the navigator the working ephemeris is the Nautical Almanac, which gives hourly Greenwich Hour Angle and declination for the Sun, Moon, planets, and Aries, plus star data, all referred to GMT (UT). Modern ephemerides derive from numerical integration of the solar system, such as the JPL development ephemeris series, from which the almanac offices tabulate the year ahead. Where the almanac stops at one year, an ephemeris program or long-term ephemeris extends the same positional data over many years for planning.