A Constellation Primer

So what is a constellation? The one most important thing is that constellations are not real -that is  they are not naturally grouped stars, but convenient memory aids, created by astronomers to be able to remember the location of stars and other objects, in other words mnemonics. So when you look up at, say the big dipper, you may well be looking at stars that are a great distance apart from each other.

Looking at the illustration on the left, and the photo on the right, it is immediately clear that identifying the constellations in the night sky is no easy task, and requires much practice. Even then, even the most experienced amateur astronomers can still doubt about some constellations. So if you are just starting out in astronomy, make this your first objective; get familiar with the constellations and don't be lured into using telescopes or finding deep-sky objects, because if you can't find the basic constellations, you're not going to find any galaxies, believe me! Get yourself a good planisphere and start practicing. Every time you go observing, even if you have a specific objective, always find time to look up and identify as many constellations as you can.

Types of constellations

Constellations can be either seasonal, or circumpolar.

1. Circumpolar constellations

Due to the movement of the Earth around the Sun, we can see different constellations in the night sky, at different moments during the year. Can you guess what the only exceptions are? Well, it's the circumpolar constellation; circumpolar means around the pole star. They are always visible at your latitude, no matter what time of the year it is. Look at this.

The circumpolar constellations never dip below your horizon, they just move in circles around the pole star. The five circumpolar constellations for northern latitudes are  Ursa minor,  Ursa major,  Drago,  Cepheus, and  Cassiopeia.

So how can you calculate what you will be able to see at your lattitude, apart from the circumpolar constellations? OK, it's this simple:  90º minus your latitude, eg. 45º, gives 45º. So your circumpolar constellations are those which lie within 45º of the pole star.
 

So for northern hemispheres, the circumpolar constellations are Ursa Major, Ursa Minor, Draco, Cepheus, and Cassiopeia. In the southern hemisphere, these constellations are never visible, just as for us in the north, the southern circumpolar constellations Centaurs, Crux and Carina will never be seen.  So it's a good idea to get  familiar with our five northern hemisphere circumpolar constellations. Remember their relative positions to each other because this will help you in turn, to remember the positions of other constellations that will dip below your horizon.