ASCENSION DEFINITION ASTRONOMY FREE

(See zenith longitude, terrestrial latitude, terrestrial).Īstronomical unit (a.u.): the radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2 p These coordinates are influenced by local gravity anomalies.

Prior to 1984, the E-terms of annual aberration (see aberration, annual aberration, E-terms of) were also added to the geometric position.Īstronomical coordinates: the longitude and latitude of a point on the Earth relative to the geoid. An astrometric position is obtained by adding to the geometric position, computed from gravitational theory, the correction for light-time. Additional small variations result from irregularities in the rotation of the Earth on it axis.Īspect: the apparent position of any of the planets or the Moon relative to the Sun, as seen from Earth.Īstrometric ephemeris: an ephemeris of a solar system body in which the tabulated positions are essentially comparable to catalog mean places of stars at a standard epoch. The rate of diurnal motion undergoes seasonal variation because of the obliquity of the ecliptic and because of the eccentricity of the Earth's orbit. Thus the position at which the object would actually be seen from the center of the Earth, displaced by planetary aberration (except the diurnal part - see aberration, planetary aberration, diurnal) and referred to the true equator and equinox.Īpparent solar time: the measure of time based on the diurnal motion of the true Sun. Altitude is 90 °Īnomaly: angular measurement of a body in its orbit from its perihelion.Īphelion: the point in a planetary orbit that is at the greatest distance from the Sun.Īpogee: the point at which a body in orbit around the Earth reaches its farthest distance from the Earth.Īpparent place: the position on a celestial sphere, centered at the Earth, determined by removing from the directly observed position of a celestial body the effects that depend on the topocentric location of the observer: i.e., refraction, diurnal aberration (see aberration, diurnal) and geocentric (diurnal) parallax. (See aberration, diurnal: aberration, annual: aberration, secular).Īltitude: the angular distance of a celestial body above or below the horizon, measured along the great circle passing through the body and the zenith. Stellar aberration is divided into diurnal, annual, and secular components.

Secular aberration is usually disregarded.Īberration, stellar: the apparent angular displacement of the observed position of a celestial body resulting from the motion of the observer. (See aberration, planetary).Īberration, annual: the component of stellar aberration (see aberration, stellar) resulting from the motion of the Earth about the Sun.Īberration, diurnal: the component of stellar aberration (see aberration, stellar) resulting from the observer's diurnal motion about the center of the Earth.Īberration, E-terms of: terms of annual aberration (see aberration, annual) depending on the eccentricity and longitude of perihelion (see longitude of pericenter) of the Earth.Īberration, elliptic: see aberration, E-terms of.Īberration, planetary: the apparent angular displacement of the observed position of a celestial body produced by motion of the observer (see aberration, stellar) and the actual motion of the observed object.Īberration, secular: the component of stellar aberration (see aberration, stellar) resulting from the essentially uniform and rectilinear motion of the entire solar system in space. Aberration: the apparent angular displacement of the observed position of a celestial object from its geometric position, caused by the finite velocity of light in combination with the motions of the observer and of the observed object.

Ascension definition astronomy