Copyright © 2007 Dorling Kindersley
Like our Sun, stars are massive globes of intensely hot gas. They produce huge amounts of energy, which is given off as heat and light. The bright stars form patterns, which we call the CONSTELLATIONS. All the stars lie so far from Earth and from each other that the distances are measured in light years. The light from our nearest star, Proxima Centauri, takes over four years to reach us. This means it lies over four light years away.
Stars vary widely in size. Our Sun is quite a small star, known as a yellow dwarf. Red giant stars are typically 30 or more times bigger in diameter than the Sun and supergiants are hundreds of times bigger. In contrast, the Sun is 100 times bigger than the tiny dense stars called white dwarfs.
If you hold up a finger and look at it with first one eye, then the other, your finger appears to move in relation to objects in the background. This happens because your line of sight from each eye is slightly different. The effect is called parallax. In the same way, as Earth orbits the Sun, our line of sight to the stars changes. Nearer stars shift relative to those further away. Astronomers measure the shift of a star’s position at different times of year and can then calculate how far away it is.
Many stars form patterns that we can recognize. We call these patterns the constellations, and many of them are named after real or mythological animals. Astronomers recognize 88 constellations, and divide the sky up into areas around each constellation. Although the groups of stars appear to be close together, they can be hundreds of light years apart. From Earth, they just appear to be grouped because they all lie in the same direction in space.
The constellation Orion is one of the most easily recognizable in the heavens. It straddles the celestial equator, so it can be seen well by observers in both the Northern and Southern Hemispheres. Northern observers see it best in winter skies and southern observers in summer skies. Betelgeuse and Rigel are its brightest stars.