Declination

The measurement of angular distances to the North or South of the celestial sphere which is an extension of the Earth's equator projected out into space. The declination is measured in degrees, minutes and seconds of arc. A planet is said to have a positive declination when it is located north of the celestial sphere and negative declination when located South of it. The value always lies between 0 and 90 degrees, with 0 degrees being a location on the celestial sphere, +90 degrees at the North Celestial Pole and –90 degrees at the South Celestial Pole. A planet's exact location can be given when the values of the declination and rectascension are taken together.

If one compares the coordinate system of the celestial Sphere with that of the Earth – the former being a projected extension of the latter out into outer space – the declination is equivalent to position of latitude on the Earth's surface.

The declination is not to be confused with the ecliptic latitude which measures the horizontal angle of a planet to the ecliptic.