Learning the constellations step-by-step

Step 2 to learning the constellations

Though the constellations in the northern part of the sky are easy to find, it’s in the rest of the sky that all the action happens. Looking south, the stars are different every month and move throughout the night. Everything moves from left to right in the northern hemisphere, so the stars over in the east are rising and will be due south in two or three hours. Those that are in the south now will be setting. They change also orientation as they rise and set. The left-to-right movement applies not just to the daily movement of the sky, If you wait until the early hours of the morning you’ll see constellations that won’t be in the evening sky for months.

Constellation movement
How the orientation of Leo changes from rising in the east to setting in the west over the course of 12 hours

So this all means that you need a map of the sky that shows exactly what is on display at the time you are observing. These days, people often use smartphone apps to show them what’s up at any particular time. These are great, because you just hold the phone up to the sky and it shows a glorious view of what it would be like without any light pollution, shows the names of the constellations and bright stars, and probably shows the position of some deep-sky objects as well. Job done, you might think. But this isn’t really learning the sky. They are an ideal short-cut to knowing the names, but you really need to find things for yourself before you can remember them. So use them as a guide only.

If you don’t have a smartphone, you can use an online map. There are two versions on the SPA website – this one, which is interactive so you can adjust it to any date and time, and this one, which shows the evening sky for this month and is aimed at Young Stargazers. Or you can download free software such as Stellarium for use on your computer.  Alternatives to online maps are the various annual stargazing almanacs, and also planispheres, which are handy circular sky maps with a mask that you can set by lining up the date and time so they show just the stars visible at that moment.

So far so good. Now you need to start picking out the constellations. One problem is that the maps are tiny compared with the real sky, but if you’ve managed to identify the Plough and Cassiopeia in the previous step you already have an idea of how the maps translate into the real thing. Now you need to start with one obvious pattern only and find that. There are particular constellations that always stand out, as shown in the examples later in this article. Our maps deliberately don’t show too many stars. Just stick to the main patterns, using the patterns shown by the lines to help you pick them out.

Now you can work from the known to the unknown, building up your knowledge bit by bit. This method is a technique called star hopping, and even experienced observers use it to find objects when using binoculars or telescopes.

Quite often there are bright planets up there as well, which are often brighter than most of the stars. Online maps and annual sky guides usually include these, which is important as often they can make the sky look quite different. The planets are only found along the line, often marked on maps, known as the ecliptic. The constellations along the ecliptic make up what’s called the zodiac, and their names are familiar to everyone as they are the ones in horoscopes.

You might think that the well-known constellations of the zodiac, such as Pisces and Aquarius, are going to be really obvious. But some of these are really obscure and faint, and are hardly visible from typical suburban skies. They were chosen on the basis of dividing up the sky into twelve sections for the purposes of astrology, rather than being really obvious. So don’t get your hopes up if you want to find Libra or Cancer from your suburban garden – they aren’t all that easy to find compared with some that you may never have heard of, such as Auriga or Cygnus.

The names

Most of the major constellations have names that have probably come down to us from the very earliest days of astronomy, when people were first studying the stars. They most likely originated in the Middle East, maybe even in pre-history, when people sat around the camp fire and told tales about the star patterns.  Orion was a hunter, Leo was a lion, and Scorpius was a scorpion from the very first writings about the sky. There are mythological stories about the constellations, though often there are several competing myths about the same one.

The star names often refer to the creatures that the constellations represent – the tail of the Lion, for example – and are mostly derived from their names in Arabic, though there are Greek and Roman names mixed in.