Circumpolar Stars

If you are in the northern hemisphere, then some stars that are close to the north celestial pole will never rise or set but simply circle around the pole once a day. These are known as circumpolar stars. Roughly speaking, these will be the stars whose declination, when added to your latitude on the earth, comes to more than 90°. For example, at latitude 40°N, all those stars with a declination greater than about 50° will circle around in the sky. The exact figure will depend upon the altitude of your northern horizon.

The same is true if you are in the southern hemisphere, except that the south celestial pole is now the relevant one, and the declination of the star (negative) plus your latitude (also counted as negative for the purpose) must now add up to less than -90°. In other words, at latitude 30°S, the circumpolar stars will be those with a declination less than about -60°.

See also:

Altitude; Celestial Sphere; Declination; Heliacal Rise.

References and further reading

Krupp, Edwin C. Echoes of the Ancient Skies, 5, 104. Oxford: Oxford University Press, 1983.

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