Why are stars grouped in constellations?

People who gazed at the skies in ancient times believed that they could see the shapes of animals and people traced out in the stars. These star groups, or constellations, have the Latin names of the shapes, and astronomers use the names in identifying stars.

But the stars in a constellation do not belong to any actual group in space and may be far apart.

The twelve constellations lying on the ecliptic, the sun’s path through the sky, are called the zodiac.

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How far away are the stars?

Stars are too far away to use kilometers or miles to measure their distances, so astronomers use light-years instead. One light-year is nearly 10 million million km, and the nearest star, Proxima Centauri, is 4 ¼ light-years distant.

The farthest heavenly bodies are at the un-imaginable distance of 8,000 million light-years! As the earth moves round the sun, the nearer stars appear to move very slightly in relation to the distant stars.

The farther apart they are, the greater the parallax (apparent movement) appears to be. By observing the various movements, astronomers are able to calculate the approximate distances of the stars from earth.

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What is a nebula?

One of the most striking objects in the sky is the Great Nebula in the constellation of Orion. It can be seen as a faint greenish patch with the naked eye just below Orion’s Belt, but through binoculars or a telescope it is seen as a mass of glowing gas.

Nebulae are large clouds of dust and gas in space. Many produce their own light, and others are illuminated by stars. Some are dark, and we see them as black clouds or bands against the stars. Many luminescent nebulae are formed when stars explode into supernovae.

The remains of the star move out through space as an expanding shell of glowing gas. Nebulae are among the most striking sights in the heavens. Photographs show them to have beautiful colors, but these colors may not show in a telescope.

The Great Nebula in Orion

The Great Nebula in Orion

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