ephemeris - Scientific ephemeris

A table giving the computed positions and brightness of an orbiting celestial object such as a planet or comet. It is calculated from the object's orbital elements, which include the orbit period, inclination, eccentricity, and positional direction of the object at the moment when the orbit crosses the equatorial plane of the primary body. The name is also used for a book, published annually, which lists all predictable astronomical phenomena for the coming year, such as planetary, lunar, and eclipse data.

An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) was, traditionally, a table providing the positions (given in a Cartesian coordinate system, or in right ascension and declination or, for astrologers, in longitude along the zodiacal ecliptic), of the Sun, the Moon, the planets, asteroids or comets in the sky at a given moment in time;

For scientific uses, a modern planetary ephemeris comprises software that generates positions of the planets and often of their satellites, or of asteroids or comets at virtually any time desired by the user.

Typically, such ephemerides cover several centuries, past and future;

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.

An ephemeris may also provide data on astronomical phenomena of interest to astrologers and astronomers such as solar and lunar eclipses, apparent retrogradation/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, Lilith, and other minor celestial bodies. 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. 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.

Scientific ephemeris

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.

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, appearent diameter in the sky, phase angle, times of rise, transit, and set, etc.

An ephemeris is usually only correct for a particular location on the Earth.