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Alpha Carinae

Proper NameCanopus
Bayer DesignationAlpha Carinae
Flamsteed NumberNone
HR (BSC)2326
Right Ascension6h 23m 57s
Declination-52° 41' 44"
Distance309 light years
95 parsecs
MagnitudeApparent: -0.6
Absolute: -5.5
Spectral ClassA9II white bright giant
Optimum VisibilityJanuary (Usually visible from southern latitudes)
NotesThe most luminous star within the Solar System's local area of the Galaxy, Canopus generates more than 13,000 times as much light energy as the Sun. It is yellow-white in colour (and indeed earlir sources prefer to classify it as an F-type yellow-white star rather than its more recent A-type white classification).

Despite its distance from the Earth (more than 300 light years), Canopus shines so strongly that it is still the second brightest star in the sky - only Sirius in Canis Major is brighter.

The origin of this star's name is not absolutely certain, but it is most likely named for Canopus, the pilot aboard Menelaus' ship when he sailed to the Trojan War to recover his wife Helen. This would make sense for a star within a constellation named for a ship (though Canopus did not in fact sail on the Argo, after which the constellation Argo Navis was named). Alternatively, there may be a connection with an old Egyptian port that also shared the name Canopus.

Imagery provided by Aladin sky atlas

Canopus is a star of an unusual type that is that is difficult to classify with specificity, and there is some disagreement over the details of its physical properties. It was conventionally categorised as a bright yellow star, and is classed as F-type in many older catalogues, but adjustments based on its rotational speed have led to a white A-type classification being preferred. Similarly, it is commonly classified in older sources as a supergiant (which would make it the closest supergiant to the Solar System) but more recent sources prefer to define it as a bright giant instead.

Regardless of the details of its classification, there is no doubt that Canopus is an immense and brilliant star. It is nearly seventy times the diameter of the Sun, meaning that, if it lay at the center of the Solar System, its outer layers would reach almost to the orbit of Mercury. It is highly luminous, producing some 14,000 times as much light as the Sun, and its surface temperature is about ten times greater than the Sun's.

Canopus is part of the Scorpius-Centaurus association, a group of more than a thousand hot stars scattered across the southern skies that share a common origin. The stars of this association are mainly spread through the constellations Scorpius, Centaurus, Lupus and Crux, all eastward of Carina, so Canopus is an outlying westward member of the group.


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