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Constellations?

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Ken Tapping, November 14, 2012

In the sky this week…

> Mars is very low in the Southwest after sunset.

> Jupiter rises around 6 pm and Venus around 5 am.

>The Moon will reach First Quarter on the 20th.

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In the library at our observatory we have a model of a chunk of space. The stars are various coloured balls hanging on strings, and everything is to scale. At one end of this model there is a little ball representing the Earth. If you look at the model from the Earth’s position you see the constellation of Orion, “The Hunter”, which we can see for real in the eastern sky these evenings. From any other direction the pattern is completely different.

The patterns of stars we have made into constellations are simply what we see from our position in space.  The stars are far enough away for those constellations to look the same from anywhere in the Solar System, but from a planet orbiting another star the sky would look different.

One other property of constellations is something anyone trying to learn them will have commented on; how could someone in our past have seen that object in that scattering of stars? Why do most constellations look nothing like what they are supposed to represent? Orion looks something like a man wearing a tunic, with a belt and a sword. However, Cygnus, “The Swan” looks like a big cross; Sagittarius, “The Archer” looks like a teapot; Hercules, the mythical hero looks like a big tombstone; Cassiopeia, “The Queen of Ethiopia”, looks like a big “W”, and Capricorn, “The Sea-Goat”, looks a lot like a boat. On the other hand, “Leo”, a spring constellation, looks quite a lot like a crouching lion, and these evenings, just below Andromeda, are three stars forming the constellation Triangulum, “The Triangle”. That one looks just like the object it is supposed to represent, and Scorpius does look quite like a scorpion.

The familiar seven-star grouping called in various countries “The Big Dipper”, “The Plough”, “Charles’ Wain”, or simply “The Saucepan” is not included because it is not a constellation; it is merely part of the constellation of “The Great Bear”, which of course does not look much like a bear.

Making constellations out of random scatterings of stars is not just something our ancestors did. In the last three hundred years or so, explorers from the Northern Hemisphere going south of the equator saw stars they had never seen before, and set up new constellations there. These include, Centaurus, “The Centaur”; Microscopium, “The Microscope”; Musca, “The Fly”; Sextans, The Sextant”; Mensa, “The Table” and Volans, “The Flying Fish”. As per normal, none of these look like what they represent, and some of the naming seems less romantic than is the case in the Northern Hemisphere. The Southern Cross looks something like a cross, but more like a kite.  Intriguingly, the Southern Hemisphere a triangle too: three stars forming Triangulum Australis, “The Southern Triangle”.

All over the world people have made constellations out of the stars in the night sky. Maybe this is part of making the great unknown more comforting or comprehensible. However irrational or illogical, putting our myths in the sky has made astronomy a much more fascinating subject. Not only does the sky contain its own mysteries, but it also says interesting things about us.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astro-physical Observatory, Penticton, BC, V2A 6J9.
Tel: 250-497-2300, Fax: 250-497-2355
E-mail : ken.tapping@nrc-cnrc.gc.ca