In astronomy, declination (abbreviated dec; symbol δ) is one of the two direction coordinates of a point on the celestial sphere in the equatorial coordinate system, the other being either right ascension or hour angle. Declination's angular distance is measured north or south of the celestial equator, along the hour circle passing through the point in question.[1
Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere. Points north of thecelestial equator have positive declinations, while those south have negative declinations. Any units of angular measure can be used for declination, but it is customarily measured in the degrees ( ° ), minutes ( ' ), and seconds ( " ) of sexagesimal measure, with 90° equivalent to 1⁄4 circle. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere.
An object at the
- celestial equator has a declination of 0°
- north celestial pole has a declination of +90°
- south celestial pole has a declination of −90°
The sign is customarily included whether positive or negative.