Circumpolar constellation

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In astronomy, circumpolar constellations are those that, from the viewer's latitude, never set. This is a very important effect to be considered in astronomy.

The celestial north pole, currently marked by Polaris, alway has an azimuth equal to zero. Also it must be noted that its altitude for a given place is fixed and its vaue is given by the following formula: A = 90-Φ. Now all star with a declination greater than A are circumpolar.

They are also visible year round at that location. From the North Pole, all constellations north of the celestial equator, (all fully visible constellations) are circumpolar, and similarly from the South Pole. From the equator, there are no circumpolar constellations. From mid-north latitudes (40-50ºN), circumpolar constellations may include Ursa Major, Ursa Minor, Draco, Camelopardalis, Cepheus, and Cassiopeia.