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The Pole Star, The North Star, Cynosura,
Alpha Ursae Minoris, 1 Ursae Minoris

Proper NamesCynosura, North Star, Polaris, Pole Star
Bayer DesignationAlpha Ursae Minoris
Flamsteed Number1 Ursae Minoris
HR (BSC)424
ConstellationUrsa Minor
Right Ascension2h 31m 49s
Declination+89° 15' 51"
Distance433 light years
133 parsecs
MagnitudeApparent: +2.00
Absolute: -3.61
Spectral ClassF7:Ib-II bright yellow supergiant
Optimum VisibilityAlways visible from northern latitudes
NotesThe main supergiant star has four known companions: two F-type dwarfs in relatively close orbits, and two others orbiting further from the primary. Polaris is a pulsating variable of the Cepheid type, the closest star of this important category to the Solar System.

A view of the pulsating supergiant Polaris. In the foreground is a much less massive dwarf star, one of several companions of the immense yellow Pole Star.

Relative Galactic Position of Polaris

The Galactic position and direction of Polaris relative to Earth's Sun. Note that, at this extreme scale, the two stars are effectively in the same place.

The famous Pole Star lies less than one degree from the Northern Celestial Pole, and so always lies north from an Earth-bound observer's point of view. Its name comes from Latin, Stella Polaris, meaning simply 'Pole Star'. Its alternative and much rarer name, Cynosura, comes from the Greek for 'tail of the dog'.

Polaris, the famous Pole Star, lies almost exactly at the Northern Celestial Pole.

Imagery provided by Aladin sky atlas

The circumpolar stars

As the Earth turns on its axis, the stars in the sky seem to turn around the Northern Celestial Pole. This image shows the paths traced by the stars as the swarm around the Pole over a period of eight hours. As the nearest bright star to the Pole, Polaris appears as the small bright crescent in the centre of the image.

Physically, Polaris is a massive star of the 'F' (bright yellow) classification. It is particularly notable as being one of the nearest Cepheid variables to Earth; it is less then half the distance of Delta Cephei itself. This is important because Polaris' four-day cycle of swelling and contraction is directly related to its mass, which is in turn related to its luminosity. This means that we can calculate the star's absolute magnitude with some certainty, and comparing this with its observed apparent magnitude, we can compute its distance. Polaris' mean absolute magnitude is -3.50, and its mean apparent magnitude is +2.11, which gives us a distance of just over 433 light years.


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