Wednesday, 14 October 2015

Astrognome Astronomy The Old North Star

The Old North Star

The North Star today is alpha Ursa Minor (the Small Bear) its name is Polaris and is the brightest star in the group. It marks the end of the tail of the small bear. To find it you have to find the pointers in Ursa Major (the Large Bear) then draw a line through them until you reach a bright star all on its own this is Polaris the North Star.

When the great pyramids were built in Egypt Polaris was not the North Star the much fainter Thuban in the constellation of Draco the Dragon had that honour. It was closest to the pole in around 2800 BC.

Although Thuban is alpha Draco it is not the brightest star in Draco. It is in fact only the 8th brightest. It is an A class giant star making it appear white in the sky,  lying at a distance of about 300 light years from Earth. Thuban can be found between the tail of the Big Bear and Kocab the fairly bright red star in Ursa Minor.

There is a suspicion that Thuban might vary in brightness, when Bayer catalogued the constellation s in 1603 it must have been brighter than Gamma which is now the brightest star in Draco.

The Earth wobbles very slightly over a period of about 26,000 years. So a line drawn from the north pole of the Earth and pointed into space will change during time.
As we have seen around 5,000 years ago Thuban was the north star, today it is Polaris in Ursa Minor, moving forward to the year 14,000 AD it will be the bright star Vega in Lyra one of the summer triangle stars that will be the north star.

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