Constellations -  Patterns in the sky !

 Looking at the night sky, it is possible to see patterns made by the brightest stars, for example lines, squares and crosses. Over 2,000 years ago, the Greeks identified certain groups and patterns of stars with various animals and characters from their myths. In about AD 140, the Greek astronomer Ptolemy listed over 40 constellations, including Orion (The Hunter) and Ursa Major (the Great Bear).

Since Ptolemy's time, new constellations have been added and astronomers today use 88, which cover the whole of the sky between them. Each constellation is a particular area of sky, not just the pattern of bright stars within it.

Stars that look close to each other in the sky are not necessarily near in space. The patterns we see from Earth are for the most part chance alignments, with some stars much further away than others.

Many of the brighter stars have individual names: Sirius, Capella and Algol, for example. From the 17th century, astronomers have also used star names that combine the constellation name with a letter of the Greek alphabet. Sirius is also Apha Canis Majoris (Alpha in Canis Major, the Great Dog) and Algol is Beta Persei (Beta in Perseus).

With the help of a simple star chart,   you can start to pick out the patterns of bright stars. Some patterns that stand out particularly well make good 'signposts' to the other stars. For instance, following the line made by the three stars of Orion's belt leads you to Aldebaran, the brightest star in Taurus, the Bull, and the star cluster of the Hyades, which appears roughly V-shaped. Following the line through further, you come to another cluster, the Pleiades, also called Seven Sisters.

Orion and Taurus are prominent constellations visible from the northern hemisphere in winter evenings. The constellations you can see at any particular time gradually change from day to day, so what you can see in the night sky in summer and winter is completely different.