The latitudinal (north-south) coordinate in the
equatorial coordinate system. Declination, denoted by the
Greek letter δ, is measured in units of degrees,
arcminutes, and arcseconds. There are 60 arcseconds in one arcminute and
60 arcminutes in one degree. It is measured with reference to the
projection of the Earth's equator onto the sky. The declination
of objects directly overhead corresponds to one's latitude on Earth, i.e. if
you are standing on the equator, objects with zero degrees declination are
directly overhead. If you are standing at the south pole, objects with
-90 degrees declination are directly overhead, and if at the north pole,
objects with +90 degrees declination are overhead. Note that Polaris,
the north star is almost-but-not-quite at a declination of +90 degrees
(according to simbad.harvard.edu, it is at +89d 15' 50.8'').
Objects which never set below the local horizon are called circumpolar.
In the northern and southern
hemispheres, they correspond to objects with declinations of
δ = +90 - (your latitude)
δ = -90 - (your latitude)
respectively, assuming that southern latitudes are negative as measured
from the equator. Thus, if you live at +40 degrees latitude, objects with
declinations higher than +50 degrees are circumpolar (ignoring obstructions
and increased atmospheric extinction near the
The longitudinal (east-west) coordinate in equatorial
coordinates is the right ascension, α.