Open Writing

I read in a newspaper recently that the glare from the night lighting in our major cities is beginning to make the stars fade from our sight. In Sydney, Australia, the 5th star in the Southern Cross can no longer be seen, and in the northern hemisphere, other well-known constellations are also affected. Before we city-dwellers forget the splendour of the night sky, let's take a look at one constellation that is recognised in both hemispheres, Orion, the Hunter.

In the northern hemisphere, he is easy to identify, with one arm raised above his head, the other holding his shield. He appears low on the horizon from late Autumn to early Spring. However, due to the tip of the earth's axis and the progression of the seasons, in Australia we see him reclining or almost upside down.

First of all, what is a constellation? It's an apparent grouping of prominent stars in the sky, which our ancestors saw as outlines of gods, mythical figures and animals. They built stories around these figures, which are the basis of modern astrology. The stars that form these constellations appear when seen from Earth to be grouped together as a two dimensional picture on a black background. However, they are not really located together in space, and are actually at vastly differing distances from us and from each other, in three dimensions. Over millennia, these groups will change shape, but from the perspective of a terrestrial watcher they appear changeless.

The grouping which we call Orion was first named by the ancient Greeks. However, other ancient civilisations have seen different forms depicted in these same stars—the Sumerians saw a shepherd, the Chinese a soldier, Indian mystics a deer, and the Egyptians saw Osiris, the God of the dead. The legend of Orion the hunter has it that he angered the sun god Apollo by the rape of his sister Artemis. Apollo created a giant scorpion, which was sent to kill him. Orion now lives in the heavens, where Scorpio is still seen chasing him.

There are seven major stars that make up Orion. They are some of the brightest stars in the sky, so are easy to see with the naked eye. However if we look a little closer, with the aid of a small telescope, much more is revealed.

The most famous star is Betelgeuse, marking Orion's right shoulder. It is a huge red giant, 300 times the diameter of our own sun, and appears to vary in brightness. 450 light-years from us, it is a star at the end of its life, and will eventually explode in a supernova. Rigel, marking Orion's left leg, is even brighter, an enormous blue-white giant. Astronomers have discovered that although Rigel appears to be a single star, it is in fact a binary, which means that two stars are locked together, endlessly circling each other. They are 773 light-years away. There are several binary stars in Orion, though most are too faint to been seen without a powerful telescope. Bellatrix on the left shoulder is 240 light-years away, and Saiph, marking the right leg is 720 light-years.

If we look at the three stars that make up Orion's belt, there are more surprises. They are called Alnitak, Alnilam and Mintaka, and are all about 1500 light years from us. As they are so much further away, but still appear bright to us, they must be immensely brighter than the other closer stars, actually 20,000 to 40,000 times brighter than our own sun.

Orion's sword, which appears to hang from his belt, is marked by three more stars. But the middle one of these is actually not a star at all. A telescope resolves the image and shows us a nebula. This is a cloud of inter-stellar gas and dust, in which new stars are formed. It is in fact a star nursery, and the light from these proto-stars shines so brightly that the whole cloud glows. The Orion nebula is also about 1500 light-years from us. When we look at objects which are so far away, it's interesting to pause and think that the light from them has taken 1500 years to reach us. Therefore we are not seeing them as they are today, but as they were 1500 years ago.

For a great picture of the Orion stars, have a look at

http://www.biochem.szote.u-szeged.hu/astrojan/orion.htm

Or drive out of the city and look up at the night sky. There's nothing like the real thing.

© Wendy Ogbourne

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Wendy writes for Bonzer! magazine. Please visit www.bonzer.org.au