· · · ·


Alpha Orionis, 58 Orionis

Proper NameBetelgeuse
Bayer DesignationAlpha Orionis
Flamsteed Number58 Orionis
HR (BSC)2061
Right Ascension5h 55m 10s
Declination+7° 24' 25"
Distance498 light years
153 parsecs
MagnitudeApparent: 0.0 to +1.6
Absolute: -5.9 to -4.3
Spectral ClassM1-M2Ia-Iab red supergiant
Optimum VisibilityDecember / January
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 nearly five hundred light years from Earth.

Older sources suggest that name comes from the Arabic ibt al jauzah, meaning 'armpit of the central one', though the more favoured modern interpretation is from yad al-Jauzā, the 'hand of Orion'. It is a particularly 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 some six hundred 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.

Size Comparison for Betelgeuse

By comparison with the Sun, Betelguese is immense. Its outer diameter changes as its composition shifts over time, but it approaches some six hundred times that of the Sun.

Imagery provided by Aladin sky atlas


Related Entries