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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Ephemeris | 1/2 | https://en.wikipedia.org/wiki/Ephemeris | reference | science, encyclopedia | 2026-05-05T08:33:24.329178+00:00 | kb-cron |
In astronomy and celestial navigation, an ephemeris (; pl. ephemerides ; from Latin ephemeris 'diary', from Ancient Greek ἐφημερίς (ephēmerís) 'diary, journal') is a book with tables that gives the trajectory of naturally occurring astronomical objects and artificial satellites in the sky, i.e., the position (and possibly velocity) over time. Historically, positions were given as printed tables of values, given at regular intervals of date and time. The calculation of these tables was one of the first applications of mechanical computers. Modern ephemerides are often provided in electronic form. However, printed ephemerides are still produced, as they are useful when computational devices are not available. The astronomical position calculated from an ephemeris is often given in the spherical polar coordinate system of right ascension and declination, together with the distance from the origin if applicable. Some of the astronomical phenomena of interest to astronomers are eclipses, apparent retrograde motion/planetary stations, planetary ingresses, sidereal time, positions for the mean and true nodes of the moon, the phases of the Moon, and the positions of minor celestial bodies such as Chiron. Ephemerides are used in celestial navigation and astronomy. They are also used by astrologers. GPS signals include ephemeris data used to calculate the position of satellites in orbit.
== History ==
1st millennium BC – Ephemerides in Babylonian astronomy. 2nd century AD – the Almagest and the Handy Tables of Ptolemy 8th century AD – the zīj of Ibrāhīm al-Fazārī 9th century AD – the zīj of Muḥammad ibn Mūsā al-Khwārizmī 11th century AD – the zīj of Ibn Yunus 12th century AD – the Tables of Toledo – based largely on Arabic zīj sources of Islamic astronomy – were edited by Gerard of Cremona to form the standard European ephemeris until the Alfonsine Tables. 13th century AD – the Zīj-i Īlkhānī (Ilkhanic Tables) were compiled at the Maragheh observatory in Persia. 13th century AD – the Alfonsine Tables were compiled in Spain to correct anomalies in the Tables of Toledo, remaining the standard European ephemeris until the Prutenic Tables almost 300 years later. 13th century AD - the Dresden Codex, an extant Mayan ephemeris 1408 – Chinese ephemeris table (copy in Pepysian Library, Cambridge, UK (refer book '1434'); Chinese tables believed known to Regiomontanus). 1474 – Regiomontanus publishes his day-to-day Ephemerides in Nürnberg, Germany. 1496 – the Almanach Perpetuum of Abraão ben Samuel Zacuto (one of the first books published with a movable type and printing press in Portugal) 1504 – While shipwrecked on the island of Jamaica, Christopher Columbus successfully predicted a lunar eclipse for the natives, using the ephemeris of the German astronomer Regiomontanus. 1531 – Work of Johannes Stöffler is published posthumously at Tübingen, extending the ephemeris of Regiomontanus through 1551. 1551 – the Prutenic Tables of Erasmus Reinhold were published, based on Copernicus's theories. 1554 – Johannes Stadius published Ephemerides novae et auctae, the first major ephemeris computed according to Copernicus' heliocentric model, using parameters derived from the Prutenic Tables. Although the Copernican model provided an elegant solution to the problem of computing apparent planetary positions (it avoided the need for the equant and better explained the apparent retrograde motion of planets), it still relied on the use of epicycles, leading to some inaccuracies – for example, periodic errors in the position of Mercury of up to ten degrees. One of the users of Stadius's tables is Tycho Brahe. 1627 – the Rudolphine Tables of Johannes Kepler based on elliptical planetary motion became the new standard. 1679 – La Connaissance des Temps ou calendrier et éphémérides du lever & coucher du Soleil, de la Lune & des autres planètes, first published yearly by Jean Picard and still extant. 1975 – Owen Gingerich, using modern planetary theory and digital computers, calculates the actual positions of the planets in the 16th century and graphs the errors in the planetary positions predicted by the ephemerides of Stöffler, Stadius and others. According to Gingerich, the error patterns "are as distinctive as fingerprints and reflect the characteristics of the underlying tables. That is, the error patterns for Stöffler are different from those of Stadius, but the error patterns of Stadius closely resemble those of Maestlin, Magini, Origanus, and others who followed the Copernican parameters."