Cassiopeia

Cassiopeia is one of the most easily recognizable constellations in the night sky of the Northern Hemisphere, its five main stars forming a distinctive W shape. 

This grouping takes its name from Greek mythology, Cassiopeia being the mother of Andromeda in the Perseus legend. She reluctantly agreed to her daughter being married to Perseus, who had rescued her from being chained to a cliff by a terrible monster, but went back on the agreement and suffered the consequences.

The constellation is an excellent example of the fact that these apparent shapes in the sky are only optical illusions and that the stars that comprise them quite often have no relationship to each other. This is apparent from consideration of Beta, Alpha  and Gamma Cassiopeia, which are 54, 230 and 610 light years away from Earth respectively.

The brightest star in the constellation is Gamma Cassiopeia, which is a fast-spinning blue-white star that has ten times the mass of the Sun but is 40,000 times more luminous.

Alpha Cassiopeia is also known as Schedar. It is a yellow-orange giant that is about 500 times more luminous than the Sun.

Beta Cassiopeia, a yellow-white giant, is also known as Caph.

Also visible in Cassiopeia (through binoculars) are the star clusters Messier 52 and Messier 103. 

M52 is an open cluster that could be anything between 3,000 and 7,000 light years from Earth. It has been estimated to contain around 200 stars.

M103 is one of the most distant open clusters known, possibly as much as 9,500 light years away. It contains more than 170 stars.

© John Welford