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Ken Tapping, September 28, 2011
In the sky this week...
> Jupiter rises around 9 p.m.
> Mars comes up around 2 a.m.
> The Moon will reach First Quarter on the October 3.
There cannot be very many of us who have never spent summer evenings lying on the ground looking at the stars, especially when camping well away from town. When doing this, most of us would have also wondered how our ancestors managed, in those random scatterings of stars, to see animals, heroes and mythical beasts. These groupings of stars are called constellations. One thing almost all constellations have in common is that they don't look much like what they are supposed to represent. Aries looks nothing like a ram, Aquila nothing like an eagle, and Auriga, with its bright star Capella which is in the north east late these evenings, looks nothing like a charioteer. However, there is a constellation high in the east these evenings that looks exactly as its name says it should; three faintish stars form a triangle, and the constellation is named Triangulum – The Triangle. Moreover, there is another one of those visible in the Southern Hemisphere – Triangulum Australe – The Southern Triangle.
The “Big Dipper” does look like a pot with a handle, and in England is often referred to as “The Saucepan”. It is also called “The Plough”, because a little imagination makes it resemble the agricultural instrument. It also looks a bit like a wagon, without wheels or horses, and is called “Charles' Wain” - Charles' Wagon. However, this clustering of stars is not a constellation; it is only part of one. The constellation containing the stars of the Dipper is Ursa Major - “The Great Bear”. If you look carefully at all the bright and faint stars in the constellation, it does look something like a large quadruped with a long snout, but not much like a bear. In particular, no bear has a tail that long. Its neighbour, Ursa Minor, the “Little Bear”, with Polaris, “The North Star” or “Pole Star” at the end of its tail, also has a ridiculously long tail. It has been suggested that the bears have long tails because that's how they were pulled up into the heavens.
Another interesting thing about constellations is that they only look as they do from our viewing point. Stars appearing close in the sky may actually be at very different distances from us. Imagine looking at the lights of a town at night from a point on a nearby hill. You can connect the lights, making “constellations”. However, if you move to another hill and look again, all your constellations will have gone, or changed into different patterns.
We have a nice demonstration in the library at our observatory. The constellation of Orion, “The Hunter”, has been set up using balls hanging on strings, arranged as they really are, with the stars at differing distances. If you look from the position of the little ball representing the Earth, you see the familiar shape of Orion, which is one of the few constellations that looks something like what it represents. However, shift your point of view and Orion vanishes; we just see an unfamiliar arrangement of stars. It's interesting how we can use the constellations to navigate our ships, and to navigate spacecraft around the Solar System. However, it won't work for interstellar travelers. Imagine what the Big Dipper might look like from the side. Imagine looking at the sky of some planet orbiting another star and seeing an exotic constellation, where one of its member stars is the Sun.