The Earth on which we live is just a tiny speck in a universe that is so vast our minds cannot even imagine how big it is. Even the sun, which is more than a hundred times as big as the Earth, is no more than a tiny speck in the universe. All the stars we can see, and billions upon billions of stars that we cannot see, are suns too. The biggest stars are called giant stars and the littlest stars are called dwarf stars. Our sun is a dwarf star, one of the very smallest. Some of the giant stars are a million times as big as our sun.
They look small in the heavens only because they are so far away. Stars are so far away that here again we have something the human mind can hardly even imagine. The sun is 93,000,000 miles from the Earth. But the nearest star is about twenty-four trillion (24,000,000,000,000) miles away. That is the nearest. Most of the stars are so much farther away that to write down the distance we would have to fill almost a page with zeros. Therefore astronomers use a different measure of distance. The speed of light is about 186,000 miles per second-nothing can travel faster than light.
The distance of a star is measured in light years. A light year is the distance light, at its rate of 186,000 miles per second, will travel in a year. The distance is about six trillion miles. Even so, most of the stars are so far away that it takes their light thousands of years to reach us.It may seem miraculous that astronomers have been able to measure this vast universe, to find out the distances of stars that are so far away, and even to tell what substances make up a particular star; but they have learned to do all these things.