In astronomy the term is used declination ( from the Latin for " diffraction " ) for a spherical coordinate for position information of celestial bodies. In the equatorial coordinate systems, the declination δ is the Elevation angle on the celestial equator. For a complete position specification in addition the right ascension or hour angle is required.

The circuit in parallel to the celestial equator, on which the celestial body is located, is called declination circle (also celestial latitude). His counterpart on earth is the geographic latitude. The angle δ the declination equal to the latitude angle φ, one can imagine the wide circle of the earth projected on the imaginary celestial sphere.

δ - values ​​north of the celestial equator are positive values ​​south of it given as negative.

The values ​​of fixed stars are substantially constant and independent of the observation. However, change in the long term due to the proper motion of the stars and the changes of the celestial equator due to the precession of the Earth's axis. Therefore, the naming of the equinox is also required for precise information.

The declination of the sun varies during the year, due to the inclination of the Earth ( according to the inclination of the ecliptic to the celestial equator ), between about 23.5 ° ( the summer solstice in June ) and approximately -23.5 ° ( at the winter solstice in December ). The same goes for the moon and the planets also lie approximately in the plane of the ecliptic.