Observing tips


How to Recognise Stars and Constellations


Astronomy, the study of stars, planets and their movements is a fascinating subject that few people understand. Learning about stars is important as we can learn about the nature, behavior of our Earth and understanding its changing climate over the past millions of years. We can learn about the origins of our solar system and even the universe itself and think about other forms of life. We can learn about unusual objects such as quasars, neutron stars and black holes. We can perhaps learn to appreciate the vastness of our universe in terms of both its size and its age. On earth, we can understand that the pull of the Moon and the Sun gives rise to tides. Stars can also used to find directions.

How to start. . .

Stars are difficult to study because they are well out of our reach. The simplest way to learn and understand something is to just look at it. Unfortunately the night skies look different every time you look up! What with the clouds, the changing positions of the Moon and the countless random pinpoints of light, it is quite forgivable to give up before you even begin! However, believe it or not, there is a system behind all this and with a little care and patience we can learn to distinguish patterns. Is it necessary to use big and sophisticated telescopes to look at the skies? No, our naked eyes are sufficient to enjoy the night skies. If binoculars are available they can be useful when observing the Moon. If you are interested in seeing detailed features on other planets then you will need a telescope.

Our sky is made up of a constant background of stars against which a few objects such as the Moon, the planets, comets and a few other objects appear to move. The word “constant” is the key to understanding the night sky. But at first glance there is no regularity. What is the problem? Firstly, clouds always seem to block our view of the sky! However, the main reason is that the star pattern itself rotates slowly westwards every night due to the rotation of the earth on its axis. (Note that this also causes the Sun to shift westwards hour by hour during the day). Together with this daily rotation there is another westward shift due to the revolution of the Earth around the Sun.

So, if you want to look for patterns made by the stars, make sure you look at the same region of the night sky at the same time for a few days consecutively. You should select a good place from where you can observe without obstruction. The best direction to view the sky for us in Tanzania is south direction, where there are many interesting stars and star patterns.

Not all of us have the time and the weather may not allow us to observe the night sky with such dedication. Then we have to take account of the slow westward shift of the sky pattern over several days. You should look at the sky one hour earlier every two weeks. If you follow these basic, (but time-consuming!) rules you should be able to make out a few patterns.

The key is to recognize standard patterns called constellations. In the southern skies, it should be possible to make out a kite like pattern of four stars called the Southern Cross. When observed for a few hours on the same night you will realize that the long side of the cross always points south. Another interesting pattern which is easy to recognize can be seen in the east, almost overhead. This is the constellation of Scorpio, the scorpion shaped constellation formed by three to four stars making up its head and a bright red star Antares in its “neck”. A long winding trail of several stars makes up its “tail”, ending in two close stars which form the “sting”. Compare what you see in the sky with the simple star map. Once you have recognized any one pattern or constellation, the star chart can lead you to another and eventually the whole sky. Try to recognize at least one star pattern every time you have a clear view of the skies you will be on your way to enjoying astronomy to its fullest.