Skywatch - Orion

Of all the constellations Orion has to be my personal favourite. To fully appreciate Orion you need a telescope but it's good viewing even with binoculars. For those of you who do have access to, or are considering buying a telescope here's what to look out for.

When choosing a telescope there are a number things to take into consideration. Perhaps most important is size and stability. It is best to buy a telescope with the largest objective lens or mirror you can afford. Usually a reflecting telescope will provide larger optics than a refractor the same size as mirrors tend to be cheaper than lenses. As a result it allows more light to your eye and you get brighter images of distant or faint galaxies.

The telescope needs to be well mounted as well for clarity of vision. If you have a limited budget you might initially opt for a reflector with a 4in (100mm) mirror. For the more serious (or wealthier) among you choose one of 8in (200mm) or more.

For those of you that don't know this is what Orion looks like.

Orion has been recognised as a distinctive group of stars for thousands of years. The Chaldeans knew it as Tammuz after the month when the familiar 'belt' first rose before the sunrise. The Syrians called it Al Jabbar (the Giant) and the Egyptians called it Sahu, the soul of Osiris. To the ancient Greeks, Orion was a giant hunter.

Artemis the goddess of the moon and the hunt, fell in love with Orion and forgot her task of lighting the night sky. Her twin Apollo saw Orion swimmingfar out at sea and challenged Artemis to hit what was no more than a dot in the waves. Artemis shot an arrow and killed him. When Orions body washed up in the waves, Artemis saw what she had done and was inconsollable. She put his body in the sky along with his hunting dogs.

The imagery of Orion is that of a hunter on one knee, holding a club in one hand and a lions head in the other. He has a belt with a sword hanging below it.

Observing with the naked eye:

Betelgeuse (alpha orionis) - The name comes from the arabic 'house of twins' apparently because of the adjacent constellation of Gemini. Betelgeuse is a variable starwhich varies in magnitude between 0.3 and 1.2 over a period of 7 years. However the semi-regular nature of the variation means changes can be observed in as little as a few weeks.

Rigel (beta orionis) - The name comes from the arabic 'foot'. Rigel is a super giant about 1,400 light years away and is about 50,000 times as luminous as the sun.

Orion Nebula (M42) - This star nursery is one of the marvels of the night sky. It is also known as the 'Great Nebula' and is plainly visible to the naked eye. It can be clearly seen with binoculars. The swirls of nebulosity spread out from its core of four stars called the 'Trapezium', which power the nebula.

Observing with binoculars:

M43 - This is a small patch of nebulosity just north of the main body of the Orion Nebula. In fact the M42 complex is simply the brightest part of a gas cloud covering the constellation of Orion at a difference of 1,500 light years.

NGC2169 - This is a small bright open cluster of about 30 stars.

Observing with a telescope:

The Horsehead Nebula (IC434) - Also known as Barnard 33 this dark nebula is projected against a background of diffuse nebulosity, alongside the bright belt star zeta orionis it can be quite difficult to see usually requiring and 8in (200mm) telescope and a dark sky.