Constellations

A constellation is a pattern of stars in the night sky that people have given a name. Most constellation names come from ancient Greek and Roman myths and show animals, heroes or objects, like Orion the Hunter, Leo the Lion or the Big Dipper. Today astronomers officially count 88 constellations, and together they cover the whole sky. Learning the constellations is a great way to find your way around the stars.

• Total constellations88Officially recognised since 1922
• Zodiac constellations12Sit along the Sun's path through the sky
• LargestHydraThe water snake, covers approx. 3% of the sky
• SmallestCruxThe Southern Cross, only visible in the south
• Oldest knownApprox. 5,000 yearsFirst catalogued by ancient Babylonians
• Brightest starSiriusIn the constellation Canis Major (Big Dog)

How were the constellations named?

Most of the constellation names we use in Europe come from ancient Greek and Roman myths. The Greeks looked up and saw the shapes of their heroes and monsters in the stars, like Orion the Hunter, Perseus, Andromeda and the Great Bear. Other cultures saw very different shapes, the same stars are a kangaroo to some Australian Aboriginal peoples and an emu in others. There is no single "right" answer; the constellations are pictures we draw with our imagination.

In 1922 the International Astronomical Union officially divided the whole sky into 88 constellations, each with a fixed boundary. Today every single star in the sky sits inside one of those 88 constellations.

Why do constellations change with the seasons?

You see different constellations at different times of year because Earth is orbiting the Sun. As we move around our star, the night side of Earth faces a different part of the sky each season. In northern winter you can see Orion clearly; in summer you cannot, because Orion is in the daytime sky, hidden by the Sun's glare. The zodiac constellations are special: they sit along the Sun's path through the sky, and the Sun appears to pass through one each month.

Tips for stargazing without a telescope

You do not need a telescope to enjoy the night sky. Some of the best stargazing is done with nothing but your own eyes and a clear, dark sky.

• Find a dark spot. Streetlights wash out fainter stars. Even a back garden away from a bright window helps. If you can get out into the countryside on a moonless night, you can see thousands of stars.
• Let your eyes adapt. It takes about 15 to 20 minutes in the dark for your eyes to reach full sensitivity. Avoid looking at phone screens. If you need to read a star chart, use a red torch (red light does not "reset" your night vision).
• Start with the easy patterns. The Big Dipper (part of Ursa Major) is the easiest northern constellation to find. From there you can find the North Star (Polaris). In the south, look for the Southern Cross (Crux).
• Use a sky app. Free apps like Stellarium show you the constellations directly above wherever you happen to be standing.

Did you know? The stars in a constellation are not actually close to each other in space. They are just in the same direction as we look out from Earth. The seven stars of the Big Dipper, for example, lie at very different distances, between about 58 and 124 light years away. If you flew a spaceship to one of them, the familiar pattern would completely disappear.

Pick a topic below to explore the constellations in more depth.