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declination

This is a fundamental term and concept in celestial navigation.

It is the latitude of the geographical position of any celestial body. Stars have very nearly constant declinations; they can have any value between N 90 and S 90. Declinations of individual stars have a very small drift over the years due to precession of the equinoxes and proper motion.

The sun's declination varies slowly throughout the year from N 23.45 to S 23.45, at a maximum rate of 1' per hour.

The declinations of the moon and planets vary in a more complex manner between about N 30 to S 30.

The N,S label is conventionally placed before the declination to distinguish it from geographic latitude, which is written with the label after the value, ie a star with declination N 19 passes over all points on earth once a day that have latitude 19 N.

See Geographical Position and see d-value.

See also Tricky Terms in Navigation.

Abbreviation:  dec

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