Declination, one of the coordinates of the
equatorial coordinate system, is the celestial sphere's analog
to latitude.
The declination of a point in the sky is that point's
angular distance from the celestial equator,
the latter of which is the plane through the Earth's equator.
Declination and right ascension (the analog of longitude)
together specify a direction, i.e., a point in the celestial sphere.
Declination is measured in degrees within the range of +90°
to -90°, with +90° corresponding to north along the direction
of the Earth's axis. The North star is approximately along
the line of this axis and has a declination just above +89°.
The celestial equator is 0° declination.
The constellationOrion spans the plane of the celestial equator,
so some points in the region assigned to Orion have a declination of 0°.
A positive declination indicates the northern hemisphere, i.e.,
if some point within celestial sphere that has a positive declination
passes through the zenith of some place on Earth, that place
is in the Earth's northern hemisphere.
Analogously, points directly above southern-hemisphere locations
have a negative declination.
The same word, declination, is used outside astronomy
with different meaning: regarding navigation on Earth using a compass,
the word indicates the angular distance between north and magnetic north,
an angle which varies over the surface of the Earth.