Tuesday, 8 September 2015

Astrognome Astronomy Alpha Capricorni

Alpha Capricorni

If you can locate the Square of Pegasus and draw a line from the top left hand star through the square and past the bottom right hand star and continue this line you will reach the brightest star in the rather faint constellation of Capricorn the Sea Goat. Capricorn is quite low down in the sky and mist will obscure your view. Its always fun to try to find these constellations!



Alpha or Al Giedi which comes from the Arabic word meaning 'billy goat 'is a naked eye double star, but it is not a tru physical double merely an optical double. Alpha (2) at magnitude 3.6 is confusingly brighter than Alpha (1) at magnitude 4.2. They are separated by 378 seconds of arc.Alpha (2) is 117 light years away while Alpha (1) is 1600 light years away. This means that Alpha (1) is actually a much brighter star, it is only fainter because it is much further away.

In ancient times the two Alphas were closer together than they are now. The closer star has moved a little bit further away from its neighbour. It was however not until the 17th century that the two stars were seen separately with the naked eye.

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