Stars and constellations

Yangdol, an eleven-year-old girl, and her twin brother Dorjay live in a village in Nubra, in Ladakh. The weather there is almost cloudless, and there is almost no air or light pollution, so the night sky is lit up with thousands of stars. Their elders tell them how some stars once helped the caravans passing through Nubra to find their way.

Look up at night and you see many stars: some bright, some dim. Stars shine with their own light. (They are not five-pointed shapes, as we draw them; they are huge round balls of hot gas, so far away that they look like points.)

Some groups of stars seem to make patterns, like the shapes of familiar things. Long ago our ancestors named these patterns after animals, objects or characters from stories, and many cultures had their own names. The shapes helped people recognise the stars.

Knowing the patterns was very useful. Before modern technology, and even before the magnetic compass, the stars helped people, especially sailors and travellers, to find directions at sea or on land, rather like a map app on a phone today. It is still used as a backup in emergencies.

In earlier times, a group of stars forming a pattern was called a constellation. Today a constellation means a defined region of the sky, which often includes such a pattern. Different cultures drew the boundaries differently, so in the early twentieth century the International Astronomical Union (IAU) agreed on one set: 88 constellations, dividing the whole sky into 88 regions. People still often use the word for the star pattern itself.