How to find Orion

The great thing about the constellation of Orion is that it’s so easy to spot, as long as you’re looking at the right time. It’s a winter constellation (a star pattern), and during the 100 Hours of Astronomy you can see it at any time from before 6 pm until the early hours of the morning. You’ll know it when you see it, because there are three quite bright stars in a line, quite close together and evenly spaced. They are at the centre of a quadrilateral of stars, including two of the brightest in the sky.

Orion over rooftops
Orion over rooftops. Photo: Robin Scagell

Where to look

If you’re looking during mid January in the evening, Orion will be rising over in the east at around 6 pm, or later in the evening it will be more to the south, and at a different angle, as these examples show:

Orion east
Orion rising in the east about 6 pm in mid January

 

Orion in south
Orion due south about 10 pm in mid January

Later still in the evening Orion will be tilting over to the west. But you’ll still be able to recognise its shape. The three stars in a line are known as Orion’s Belt, for reasons that date back possibly thousands of years, when most of the major constellations were first described. The patterns that we see in the sky are virtually the same as they saw then, except that with no light pollution people would have seen them much more easily.  People would have told tales around the camp fire just as we watch stories on the TV today. But with no books or writing available, they would have used the patterns of stars themselves as a story board.

So it is with Orion, the Hunter. Many different civilisations saw this pattern as some sort of hunter or giant, though the name Orion dates from ancient Greek times. He is usually shown facing to the right, facing the constellation of Taurus, the Bull, with an upraised shield with a lion’s head marked by a curved line of stars, and a raised club in his other hand.

Constellation figures for Canis Major, Lepus, Orion and Taurus superimposed on the stars. Artwork by Richard Bizley

And here’s a map of the whole sky for 12 January at 8 pm. Because it’s designed for looking above you rather than at the ground, east and west are reversed compared with a conventional map.

Sky for 12 Jan 2019
Map created using Stellarium software

Find the Orion Nebula

Once you’ve found Orion itself, look for the Orion Nebula. This is below the thee stars that mark Orion’s Belt, and in a dark sky you can see it with the naked eye. But even from a light-polluted location you can get a glimpse of it using binoculars. But don’t expect to see the glorious colours that you see in photos – our eyes just aren’t sensitive enough to see them.

Orion Nebula finder
The three stars of Orion’s Belt are your guide to locating the Orion Nebula. Photo: Robin Scagell

The photo shows roughly what you’ll see through binoculars. The nebula itself is fainter than it shows in the photo, but you should be able to see that the middle star of the three that hang down from the Belt of Orion is slightly hazy.

This area is the birthplace of stars, and all the bright stars of Orion (with the exception of Betelgeuse at top left) are very bright and young stars that have been born in this area within the past few million of years. But don’t expect to see a new star suddenly pop into existence – the process takes hundreds of thousands of years. Here’s a close-up photo made with a telescope:

M42
The Orion Nebula (catalogue number M42) as photographed through a 200 mm amateur telescope. Photo: Robin Scagell

Star colours

Compare the colours of the bright stars at top left and bottom right of the pattern, Betelgeuse and Rigel. Can you spot the difference? Betelgeuse is noticeably redder than Rigel. This difference is due to the temperatures of the two stars. Betelgeuse is what’s known as a red supergiant, and although it has swollen up to giant size, its temperature is comparatively low, about 3500 K (K means Kelvin, the scientific temperature scale which is like Celsius but which starts from absolute zero, about –273º C). This is about the same temperature as a halogen light bulb. Rigel, on the other hand, has a temperature of around 12,000 K.
Betelgeuse is in the last stages of its life as a bright star. In the not-too-distant future it will become a supernova, and will outshine all the other stars in the sky, and become visible even in daylight. Then after a few months it will fade away to obscurity. This could happen at any time – any time, that is, within the next million years or so. It could even happen during the 100 Hours of Astronomy – but then again, it probably won’t!

Orion
Compare the colours of Betelgeuse and Rigel

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