The favourite constellation of the Australian summer, Orion, is still prominent in the evening sky of autumn

March 14, 2012

Orion_12 March 2012_Nick Lomb

The constellation of Orion imaged on the evening of 12 March 2012 with the main stars labelled. Image and copyright Nick Lomb ©, all rights reserved

There is a lot to see in the evening sky this March 2012. The Moon is out of the way until near the end of the month and the two brightest planets Venus and Jupiter are close together in the north-west. On the other side of the sky Mars is still bright in the east after its recent opposition. The planets are augmented by the International Space Station making bright evening passes and there are occasional bright flashes from Iridium satellites.

Among all this activity it is also worth looking at some old favourites such as the constellation of Orion that is prominent high in the western sky. Orion is one of the easiest constellations to recognise with four bright stars in a rectangle and three stars in a row in the middle. In Australia many people refer to part of the constellation as the Saucepan – the three stars of the belt form the base and the dagger with the Great Nebula of Orion in the middle represent the handle.

The international GLOBE at night project wants people to observe one of two or three constellations in the evening sky to report on the brightness of their sky. Orion is one of the two southern hemisphere constellations available for this purpose. There are two opportunities left this year to contribute, until 22 March 2012 and 11 to 20 April 2012. Contributing an observation is easy to do and there is a cool webapp so that observations can be submitted in real-time.

The brightest star in the constellation is the blue supergiant Rigel that represents the left foot of the giant Orion according to Greek mythology. Strangely, the star is named Beta Orionis even though it is the brightest star. It is at a distance of 860 light years from us and radiates 85 000 times as much energy as our Sun. There is a faint companion that is itself double and is so far from the main star that it takes over 20 000 years to make one circuit.

The Alpha star in the constellation and the second brightest star is the huge red supergiant Betelgeuse. It is so huge that if it replaced the Sun it would engulf all the four inner planets, Mercury, Venus, Earth and Mars. It is at a distance of about 570 light years and radiates 85 000 times as much energy as our Sun.

Another one of the four stars forming the outer rectangle of Orion is Saiph. This star is a blue supergiant like Rigel, but even hotter. This high temperature means that more of its energy is radiated as ultraviolet and so it appears fainter than Rigel to our eyes.

The fourth of the stars forming Orion’s rectangle is Bellatrix. This is again a hot blue star that at a distance of 240 light year is closer to us than most of the other stars in Orion.

Finally, let’s mention Meissa that according to the old mythological drawings is the head of the giant Orion. This is a double star with one component being a rare O-class star with the extreme temperature of about 35 000 Kelvin while its companion is a little cooler 27 000 Kelvin. (The Kelvin temperature scale used by astronomers is the same as the ordinary Celsius scale, but with 273 added so that the freezing point of water is at 273 K.)

So on these dark autumn evenings once you had your fill of the bright planets and satellites, have a look at the giant Orion and then maybe report what you see to Globe at Night.

Reference: Stars by Jim Kaler


20 responses to “The favourite constellation of the Australian summer, Orion, is still prominent in the evening sky of autumn

  • Hi my name is Marianne. While I was traveling in a plane on my way home from Hong Kong to Adelaide in the early hours of the 10th October 2016 I saw an amazing sight of stars. I couldn’t believe what I was seeing through my window. I noticed 3 very bright stars in a row but many more stars that looked to be in a dome of stars. I did some googling and maybe I saw the celestial sphere ( dome of stars ) and for sure I saw Orion’s Belt. I’m sure at that time I was flying near the equator. I would love to know more about what I saw, if it is rare to see and if I might ever see that again. Regards Marianne.

    • Marianne, the three stars probably were Orion’s belt. The celestial sphere is the whole (imaginary) sphere on which all the stars can be imagined to be placed. We see this apparent dome from anywhere. Maybe you were looking at the arc of stars at the end of Orion’s arm – they represent a shield or the pelt of a lion, but look more like a bow to me! The sight of Orion in the east is not rare and is available any spring evening around midnight.

  • Hi and thank you for the article above.

    Since I was a teenager (I’m 72 now), I’ve always looked to the skies at night, hoping to find my favourite group of stars. Looking up at what I now know to be the Orion Belt cluster, I saw a bull’s head. To me, it’s always been ‘The Bull’.

    The three most distinguishable stars are the 3 stars in a row, which are the bull’s snout (or nose). Rigel was the top part of the bull’s neck and Cursa was the bottom part. The Great Nebula were the eyes and Saiph was the tip of the horn/s.

    Betelgeuse was just a weird movie to me (and I paid little attention to that star in the heavens below my bull’s head). Bellatrix may well have come from the comic strip of Asterix, which also never entered the realm of my vision when looking up at ‘my bull’.

    I always knew that what I was looking upon in the night sky had to be something special and to just find out now (sorry… I never bothered to check things out until now), I’m pleased that at last I know its name and what it means to the stargazers here on earth.

    Thank you again for this great article.

    Warm regards,

    • Frank, Thank you for your post. With your description I can also see your Bull in profile, particularly when Orion is low in the western sky. In fact it looks much better than Taurus, the ‘official’ Bull. It is a reminder that the constellations we use today are simply the set that astronomers agreed to use in the 1930s, that there are many other interpretations and that you are, of course, free to make up your own patterns if you wish!

  • Me and my Family were outside looking through my telescope and then I saw the saucepan. I recognised it straight away because I learnt about it at school last year. I did some more reasearch as soon as I saw it and found out it was connected Orion.

  • Me and my dad were outside looking through my telescope and I then saw the constellation of the saucepan. I recognised it straight away because I learnt it at school last year.

  • Is there a star called the Northern Star? It was the name of my Stallion and I have called his son Orion’s Reflection which is why I was looking up the constellation of Orion.

    • Hello Bronwyn. There is a star called the Northern Star, but it is not visible from Australia. Also known as Polaris, it is the star about which all stars in the northern hemisphere sky appear to circle. Orion’s reflection is a nice name; in the constellation of Orion there are a number of what are called “reflection nebulae” such as the beautiful Messier 78.

    • Hello D. In Greek mythology Artemis was the goddess of the hunt and Orion was her hunting companion. According to one version of the story she was in love with Orion, but killed him accidentally.

  • I live in Spain and my son has just last week arrived in Perth, He learnt from me the beauty of the nite sky, and when he told me he could see Orion I doubted him, he said its upside down and I really thought he has really lost it, well now I know different, Well impressed with this web site and the information gleaned,

    • Thanks for your comments John. I am pleased that you like the Sydney Observatory website for we do try to provide useful and interesting information. Now that it is early summer in Australia Orion is once again prominent in the eastern sky. And yes it is upside down compared to the view that you are used to from the northern hemisphere.

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