The position is given to astronomers in a spherical polar coordinate system of right ascension and declination or to astrologers in longitude along the zodiacal ecliptic, and sometimes declination. Astrological positions may be given for either noon or midnight.
An astronomical ephemeris may also provide data on astronomical phenomena of interest to astrologers and astronomers such as 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 sometimes even the position(s) of Chiron, and other minor celestial bodies.
Astrologers also use other ephemerides that include tables of imaginary celestial bodies, such as Lilith, a term they use variously for the apogee of the Moon or the second focus of the Moon's orbit. Some ephemerides also contain a monthly aspectarian, while others often include the declination of the planets as well as their longitudes, right ascensions, or Cartesian coordinates.
Typically, such ephemerides cover several centuries, past and future; the future ones can be covered because celestial mechanics is an accurate theory. Nevertheless, there are ''secular phenomena'' which cannot adequately be considered by ephemerides. The biggest uncertainties on planetary positions are due to the perturbations of numerous asteroids, most of whose masses and orbits are poorly known, rendering their effect uncertain. Reflecting the continuing influx of new data and observations, the JPL has to revise its published ephemerides at intervals of 20 years.
Solar system ephemerides are essential for the navigation of spacecraft and for all kinds of space observations of the planets, their natural satellites, stars and galaxies.
Scientific ephemerides for sky observers mostly contain the position of the mentioned celestial body in right ascension and declination, because these coordinates are the most often used on star maps and telescopes. The equinox of the coordinate system must be given. It is in nearly all cases either the actual equinox (the equinox valid for that moment, often referred to as "of date" or "current"), or that of the one of the "standard" equinoxes, typically J2000.0, B1950.0, or J1900. Star maps are almost always in one of the standard equinoxes.
Scientific ephemerides often contain further useful data about the moon, planet, asteroid, or comet beyond the pure coordinates in the sky, such as elongation to the sun, brightness, distance, velocity, apparent diameter in the sky, phase angle, times of rise, transit, and set, etc. Ephemerides of the planet Saturn also sometimes contain the apparent inclination of its ring.
An ephemeris is usually only correct for a particular location on the Earth. In many cases the differences are too small to matter, but for nearby asteroids or the Moon they can be quite important.
Global Positioning System (GPS) navigation satellites transmit electronic ephemeris data consisting of health and exact location data that GPS receivers then use (together with the signal's elapsed travel time to the receiver) to calculate their own location on Earth using trilateration.
Other modern ephemerides recently created are the EPM due to the Russian Institute for Applied Astronomy of the Russian Academy of Sciences, and the INPOP ones by the French IMCCE.
Though astrology is and always has been geocentric, heliocentric astrology is an emerging field; for this purpose a standard ephemeris cannot be utilized, and because of this specialized heliocentric ephemerides must be calculated and used instead of the default geocentric ephemerides that are used in standard Western astrology to construct the astrological chart/natal chart.
Category:Astrological texts Category:Astrometry Category:Astronomy books Category:Calendars Category:Technical factors of astrology
ca:Efemèrides cs:Efemeridy da:Efemeride de:Ephemeriden et:Efemeriid es:Efemérides eo:Efemeridoj fr:Éphéméride (astronomie) gl:Efeméride hy:Էֆիմերտե io:Efemerido it:Effemeridi lb:Ephemeriden lt:Efemeridės hu:Csillagászati évkönyv nl:Efemeriden ja:天体暦 no:Efemeride pl:Efemerydy (astronomia) pt:Efeméride ro:Efemeridă ru:Эфемерида sk:Efemerida sl:Efemeride fi:Efemeridi sv:Efemerid th:ปฏิทินดาวเคราะห์ uk:Ефемерида vi:Lịch thiên văn zh:星曆表This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
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