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Alpha Orionis, 58 Orionis

Proper NameBetelgeuse
Bayer DesignationAlpha Orionis
Flamsteed Number58 Orionis
HR (BSC)2061
Right Ascension5h 55m 10s
Declination+7° 24' 25"
Distance427 light years
131 parsecs
MagnitudeApparent: +0.3 to +0.6
Absolute: -5.3 to -5.0
Spectral ClassM2 Red Supergiant
Optimum VisibilityJanuary
NotesPulsating semiregular variable with a period of 2,335 days

One of the most famous stars in the sky, Betelgeuse is a gigantic red star lying more than 400 light years from the Earth.

Its name comes from the Arabic ibt al jauzah, meaning 'armpit of the central one'. It is particular bright and prominent star (the tenth brightest in the sky) and shines with a red-orange light. With Bellatrix, it forms the shoulders of Orion the Hunter.

Image of Betelgeuse

The mottled surface of Betelgeuse, a vast and ancient star approaching the end of its long life cycle.

Betelgeuse is a truly immense star. It is in fact one of the largest stars known, with a diameter up to one thousand times that of the Sun. This diameter is not fixed: the matter in Betelgeuse's outer shells swells and contracts by up to a quarter of its volume, over an irregular period of about five years. This factor is reflected in its shifting magnitude when viewed from Earth. Patterns of 'starspots' have also been detected on Betelgeuse's surface.

Betelgeuse, the eastern shoulder of Orion and the second brightest star in that constellation after Rigel to the south.

Betelgeuse is a star in the last stages of its life. It has evolved to the point where its raw material for nuclear fusion has almost been exhausted, and it is approaching the point - a matter of just a few million years from now - where a supernova will occur.


A view of the red giant Betelgeuse, against the backdrop of the Milky Way.

Relative Galactic Position of Betelgeuse

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


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