Constellation of Orion
The constellation of Orion is in prime position at this time of year and is perhaps the most readily recognisable of all the constellations. Read on to learn about Orion, the great hunter of the night sky...
Two stars compete with each other to be the finest in the constellation, Alpha Orionis, or Betelgeuse (pronounced beetle-juice); and Beta Orionis, or Rigel. Betelgeuse is one of the largest stars to be seen in the sky. If it were placed where the sun is, it would engulf Earth and nearly reach Mars. It is clearly red, and it is variable. At maximum brightness it reaches a magnitude of 0.5, but can fade to below 1 over an irregular period over about 5 or 6 years. Betelgeuse was the first star to be directly imaged as a disk from Earth by the Hubble Space Telescope. Rigel is diametrically opposite Betelgeuse in the star pattern, and is brighter - shining bluish white at a magnitude of 0.1 The other bright stars in Orion are also named Bellatrix, Mintaka, Alnilam, Alnitak and Saiph.
The whole constellation sits in a tenuous gas cloud that spawned its white-hot stars. Orion is rich in doubles and multiples. Theta Orionis can be separated in a small telescope. Iota Orionis is also a double. Sigma Orionis appears double in binoculars, but small telescopes show it to be a triple, with white, bluish and reddish components. Larger instruments separate a fourth component. The easiest variable to find is the very red W Orionis at the southern end of the arc of the six Pi stars that form Orion shield.
Orion's Belt is made up of three serried stars: Delta, Epsilon and Zeta Orionis. Just below this slanting row is a misty patch. Binoculars show it to be a bright nebula, M42. Long-exposure photographs bring out its staggering beauty. A much smaller, nearly round nebula, M43, lives close to the Great Nebula. South of Zeta Orionis is the glowing IC 434 which has the form of a horses head.
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