Friday, 2 October 2015

Astrognome Astronomy, Cassiopeia


Nearly as famous as the Great Bear, Cassiopeia is nearly as prominent. It is also a very interesting group. It`s five main stars form a letter ‘W’ or ‘M’ depending on which way you view it.

In mythology Cassiopeia was a queen who boasted that her daughter Andromeda was prettier than the nymphs who lived in the ocean. Since the nymphs were the children of Neptune it got her in a lot of trouble. Neptune sent a monster to attack her land; Cassiopeia was told the only way to save her land was for Andromeda to be chained to a rock so the monster could eat her. At the last minute Perseus riding the winged horse Pegasus arrived he had just killed the Medusa and still carrying the head showed it to the monster who turned to stone. Perseus rescued Andromeda they were married and lived happily ever after.

This story is so famous they even made a film called ’The Clash of the Titans’. All these characters even the monster is in the sky.

Cassiopeia is on the opposite side of the North Star to the Great Bear. When the bear is high up Cassiopeia is low down and vice versa. During autumn evenings Cassiopeia can be seen at its best. The five main stars are of the second or third magnitude which makes them easy to find and in any case the letter W is easily found in the sky.

The Big Dipper is the Great Bear

Gamma Cassiopeia the middle star in the W is a variable star of a very strange nature. It is normally about magnitude 2.2 but it has experienced occasional outbursts rising to a brightness of magnitude 1.5 in 1935 and outshining the North Star and has fallen to a magnitude of 3.2 completely changing the appearance of Cassiopeia.
Gamma Cassiopeia is the prototype star of a small class of Gamma Cassiopeia type variables. These stars are hot B class stars, much hotter than our Sun.
Another variable star but much fainter is Rho Cassiopeia which lies close to Beta and is flanked either side by Tau and Sigma. Usually Rho is of the 5th magnitude but on rare occasions it can fall to below naked eye visibility. This happened in 1893, 1948 and 2000.

Rho is a yellow hypergiant star about 8,000 light years away and about 500,000 times a luminous as the Sun, there are less than 20 of this type of star known in our galaxy.

There is a nice open cluster of stars M52 in Cassiopeia. It was discovered in 1774 by Charles Messier. There are around 200 stars in the cluster which is about 5,000 light years distant. It is close to the star 4 Cassiopeia and can  be found in binoculars.

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