Declination

Declination (dec) is an astronomical term associated with the equatorial coordinate system. Dec is comparable to latitude, projected unto the celestial sphere, and is measured in degrees north of the celestial equator. Therefore, points north of the celestial equator have positive declination, while those to the south have negative declination.

An object on the celestial equator has a dec of 0°.
An object above the north pole has a dec of +90°.
An object above the south pole has a dec of −90°.

Note that the sign must be included even if positive.

A celestial object that passes over zenith, has a declination equal to the observer's latitude, with northern latitudes yielding positive declinations. A pole star therefore has the declination +90° or -90°. Conversely, celestial objects with a declination higher than , where l is the latitude, are visible the whole sidereal day. Such stars are called circumpolar, while the phenomenon of a sun not setting is called midnight sun.

Table of contents

1 Varying declination

1.1 Sun
1.2 Moon
1.3 Stars

Varying declination

The declination of all celestial objects vary over time, in different periods.

Sun

's path over the celestial sphere changes with the varying declination during the year, marking the Azimuths in °N where the sun rises and sets at summer and winter solstice at a place of 56°N latitude.]] The declination of the Sun varies with the seasons. The declination equals +/- the tilt of the earth axis, and has it maximum at the northen hemisphere summer solstice and the minimum at winter solstice. The extreme values are +23°26' and -23°26' respectively. The declination of the sun at the equinoxes is +/-0°.

Moon

The Moon also has an annual cycle, with maximum declination at northern hemisphere midwinter and minimum at midsummer. There is also a approximately 19 year long cycle, varying the maximum declination from +28°35' to +18°18' and the minimum from -18°18' to -28°35'.

Stars

The Stars have approximately the same declination from year to year, and vary in whole degrees after passing of centuries.