When you first turn your attention to the night sky, it is easy to think that the stars are simply tiny pinpoints of light, randomly scattered in the inky blackness. However, when you look through the star charts and you will soon realize that the stars can be recognized by the patterns they form and the way in which one group relates to another.
In the Northern Hemisphere, the important star guides are the Plough (Dipper) section of Ursa Major, the W of Cassiopeia, the T of Cepheus and the box of Perseus. Once these have been located, you should be able to find the square of Pegasus, and from it Aries, Taurus and Cygnus.
Note, too, the constellations with bright stars - Lyra with Vega, Taurus with Aldebaran, Boötes with Arcturus, Auriga with Capella, Leo with Regulus and Canis Major with Sirius. Orion with Betelgeuse and Rigel is probably the easiest constellation to find after the Plough (Dipper).
For observers in the Southern Hemisphere, Crux (the Southern Cross) acts as the first reference point. Nearby is Carina (the Keel) with Triangulum on the other side. Also notable are Aquarius, Vela (the Sails), the box, or 'body', of Corvus (the Raven) and the nearby box of Crater (the Cup).
Observers in the Southern Hemisphere also have the Large and Small Magellanic Clouds to guide them. The Small Cloud lies on the opposite side of the South Celestial Pole to Crux, and north of it are Tucana (the Toucan), then Phoenix and Cetus (the Whale). The Large Cloud is close to Volans, and north of it are Lepus (the Hare) and Orion.
Other guides in the night sky are the planets. When possible, look for Mars, Jupiter and Saturn.
To find out when specific constellations are visible, a planisphere is needed. Remember that at the same time one month later, each constellation will have moved westward by 30° . Stars at right ascension 0 hours will be due south at 10pm on 22 March; those at RA 2 hours will due south at the same time on 22 April, at RA 4 hours on 22 May, and so on. In other words, there is a 30° shift in right ascension every month. With this in mind, and by looking at the star charts, you can work out which constellations lie due south at any time of the year.
(above) A planisphere shows on a flat surface the stars visible at certain dates and times. (left) The planisphere shows visible stars in Northern Hemisphere in London in mid-December. (right) The planisphere shows stars in Southern Hemisphere in Adelaide and Cape Town in mid-June.
