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

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

Published by Nick Lomb on March 14, 2012 9 Comments

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

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9 Responses to “The favourite constellation of the Australian summer, Orion, is still prominent in the evening sky of autumn”

  1. April 16, 2014 at 5:16 pm, Bronwyn said:

    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.

    Reply

    • April 16, 2014 at 5:23 pm, Nick Lomb said:

      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.

      Reply

  2. March 17, 2014 at 2:46 pm, Death said:

    LOL

    Reply

    • March 17, 2014 at 3:13 pm, Nick Lomb said:

      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.

      Reply

  3. December 11, 2013 at 8:37 am, John Mack said:

    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,

    Reply

    • December 11, 2013 at 11:59 am, Nick Lomb said:

      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.

      Reply

  4. November 13, 2013 at 11:17 pm, Izzy said:

    Dude it’s been over a year, when’s the update?

    Reply

    • November 14, 2013 at 10:57 am, Nick Lomb said:

      Hello Izzy. Stars like the stars of Orion do not change in human timescales so there is no obvious need to update this post. Sydney Observatory does provide regular monthly sky guides so that people know what to look for in the sky during any month of each year.

      Reply

      • March 17, 2014 at 2:36 pm, Death said:

        Is Orion a hunter of Artimis ?

        Reply

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