I
like stars. No, not the stars in Hollywood, but
the ones that shine in the night sky. T ese stars sparkle like jewels in the dark. Without them, life on Earth wouldn’t exist. One star, our sun, lights and heats Earth.
T e sun looks so diff erent from other stars because it’s so close to us. But if we were far away, the sun would look much like the stars we see at night. Without the sun, Earth would freeze, and life on Earth wouldn’t exist. But even before the sun and Earth existed,
other stars were making the material that would make life on Earth possible. How? T ey formed most of the atoms, or particles of matter, that make up our bodies. Stars made the oxygen we breathe and the iron in our blood. When these stars died, they cast oxygen, iron, and other materials into space. T ese elements eventually became space clouds called nebulae. Over time, new stars and planets formed in them.
Searching Space Stars are created in the space between other stars. If you go out tonight and look at the black space between the stars, you might think it’s empty. And you’d be nearly right. To see how empty, imagine a cubic centimeter, which is about as small as a sugar cube. One cubic centimeter of the air you breathe has 50 quintillion (50,000,000,000,000,000,000) atoms. But a typical cubic centimeter of the space between the stars has only one atom. How can such an empty place make a star?
Aſt er all, most stars are huge. T e sun is so big that you could put Earth, the moon, and all the space between them inside it and still have lots of room leſt over. Well, the secret to space is simple. Space is
enormous. So all those atoms between the stars add up. In our galaxy, the total amount of those atoms has a mass of between 5 billion and 10 billion times more than the sun. To make a star, this matter must gather into
a cloud, or nebula, in space. Nebula is Latin for “cloud.” But not all space clouds make stars, just as not all clouds in the sky make rain.
12 NATIONAL GEOGRAPHIC EXPLORER
Star-making nebulae are dense, at least
by the standards of space. T ey’re still much thinner than the air you breathe. But dense clouds can collapse, creating the right conditions for a star. Most space clouds are too fl uff y to collapse.
T ey are made up of individual atoms. Most of these atoms are hydrogen, which is the lightest gas. Instead, to fi nd places where stars are born, we need to go to space clouds that have molecules. A molecule is something with two or more atoms joined together. On Earth, the air you breathe is made up of
molecules. T e two most common elements in Earth’s air are nitrogen molecules (two nitrogen atoms joined together) and oxygen molecules (two oxygen atoms joined together). In space, the most common molecule is hydrogen (two hydrogen atoms joined together).
The Hubble Space Telescope has taken dramatic pictures of space clouds, such as the Eagle Nebula seen here.
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