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In astronomy, declination (abbreviated dec; symbol δ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or south (negative) of the celestial equator, along the hour circle passing through the point in question. [1]
In the standard (non-flipped) images, this is a counterclockwise measure relative to the axis into the direction of positive declination. In the case of observed visual binary stars , it is defined as the angular offset of the secondary star from the primary relative to the north celestial pole .
Star position is the apparent angular position of any given star in the sky, which seems fixed onto an arbitrary sphere centered on Earth. The location is defined by a pair of angular coordinates relative to the celestial equator: right ascension (α) and declination (δ). This pair based the equatorial coordinate system.
The Right ascension of the star is about 18 h. 18 h means it is a March early-hours star and in blue sky in the morning. If 12 h RA, the star would be a March all-night star as opposite the March equinox. If 6 h RA the star would be a March late-hours star, at its high (meridian) at dusk.
The location of stars, planets, and other similarly distant objects is usually expressed in the following parameters, one for each of the three spatial dimensions: their declination, right ascension (epoch-fixed hour angle), and distance. These are as located at the vernal equinox for the epoch (e.g. J2000) stated. [2]
Then the star's approximate position, suitable for identification purposes, is given in terms of declination and sidereal hour angle, followed by the star's magnitude. The final column presents citations to the sources of the data, The American Practical Navigator and the star's entry at the SIMBAD database, a project of the Strasbourg ...
δ - Dec, declination, if the Greek letter does not appear, ä letter will appear. P or P orb or T - orbital period; a - semi-major axis; b - semi-minor axis; q - periapsis, the minimum distance; Q - apoapsis, the maximum distance; e - eccentricity; i - inclination; Ω - longitude of ascending node; ω - argument of periapsis; R L - Roche lobe ...
Equirectangular plot of declination vs right ascension of the modern constellations with a dotted line denoting the ecliptic. Constellations are colour-coded by family and year established. Constellation families are collections of constellations sharing some defining characteristic, such as proximity on the celestial sphere , common historical ...