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About this video

Lie on your back on a dark night and look at the stars for a while, and your eyes start joining them up. People have done this for thousands of years, all over the world. A group of stars that people joined into a picture and gave a name is a constellation. One of the easiest to find is Orion, the hunter: three bright stars in a short straight row make his belt, and four more make his shoulders and knees. One shoulder, Betelgeuse, shines a little orange, and one knee, Rigel, a little blue.

Nobody drew those lines in the sky, so different people saw different pictures. The seven stars Americans call the Big Dipper are a plough in Britain and seven wise men in India. Today astronomers everywhere use one list of 88 constellations, so a star in Orion means the same place in the sky for everyone. And the stars of a constellation are not neighbours. Orion's belt stars are several times farther from us than Bellatrix, the star on his other shoulder. They only look close together because they lie in nearly the same direction from the Earth. Fly to another star and look back, and Orion would fall apart.

Which constellations you see changes through the year. At night your side of the Earth faces away from the Sun. In December the Earth is between the Sun and Orion, so Orion is up in the evening. In June Orion is behind the Sun, and the night shows the Scorpion instead. In the northern half of the Earth, follow the two stars at the front of the Big Dipper's bowl about five times the gap between them to reach the North Star. This video goes with the lesson Constellations in Astronomy Level 1 on Knaph.

Transcript

1. 0:00Look at the stars for a while and your eyes start joining them up. This is Orion, the hunter. Three stars make his belt. One shoulder, Betelgeuse, is a little orange. One knee, Rigel, a little blue. Nobody drew those lines.
2. 0:16So different people saw different pictures. Americans see a big ladle, the Big Dipper. In Britain it's a plough. In India, seven wise men. Today astronomers use one list of 88 constellations.
3. 0:32The stars of a constellation look like neighbours, but most of them aren't. Orion's belt stars are several times farther from us than Bellatrix, on his other shoulder. They only look close together because they are in nearly the same direction. Fly to another star and look back, and Orion would fall apart.
4. 0:54At night, your side of the Earth faces away from the Sun. In December the Earth is between the Sun and Orion, so Orion is up in the evening. In June it is on the other side. Orion is behind the Sun, lost in daylight, and at night you see the Scorpion instead.
5. 1:16In the northern half of the Earth, find the Big Dipper. Follow the two stars at the front of its bowl, about five times the gap between them, and you reach the North Star.
6. 1:32A constellation is a picture we see from here.