Orion

Orion is a winter constellation and few would dispute the status of Orion as the finest constellation in the sky. Only a few of the 88 constellations possess even one star of the first magnitude. Orion has two, the red supergiant Betelgeuse and brilliant white Rigel, as well as five further stars of the second magnitude. Three of the second magnitude stars form a striking alignment which has been associated since ancient times with the belt of a mighty hunter. The nebulous glow surrounding the two stars below the belt represents Orion’s sword. Betelgeuse and another second magnitude star, Bellatrix, mark his shoulders, and Rigel and the final second magnitude star, Saiph, his knees.

Despite the brilliance of his stars, Orion is a curiously obscure figure in ancient mythology. Hercules for instance, is a “superhero” with far better credentials, but is represented by a constellation that possesses no star brighter than the third magnitude.

Most of Orion’s brightest stars are physically associated, travelling together in the same direction through space. These are very luminous stars compared with our own Sun and also very young, having been born only a few million years ago in the vast region of gas & dust that festoons much of the constellation, but which is centred on the Great Orion Nebula, M42, located in the sword region. Star birth is still continuing in M42 and it is one of the very finest objects in the sky for small telescopes.

As well as M42 and the other areas of nebulosity, Orion boasts a great number of other interesting sights for binoculars and amateur telescopes. Rigel and two of the belt stars, Mintaka and Alnitak are telescopic doubles. Sigma Orionis, the fourth magnitude star just below Alnitak is a multiple system, four members of which can be seen with small telescopes and there is a fainter triple in the same low power field. An even more famous multiple system is at the heart of M42. This is Theta 1 Orionis, better known as “The Trapezium”. One of the most famous objects in Orion, the Horsehead Nebula, is however very difficult to see without a special filter.

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