The latitudinal (north-south) coordinate in the astronomical 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, 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 horizon).

The longitudinal (east-west) coordinate in equatorial coordinates is the right ascension, α.