Billions of stars which we see in the sky every night are made up of hot gases. Even the Sun is a star. However, there are stars which are million times more shining than the Sun, but they don’t appear so because of their greater distances from the earth. The stars are of varying sizes.
We measure the distance of stars in units of light years. A light year is the distance travelled by light (its velocity being 3 x km or 3 hundred thousand km per second) in one year. The star nearest to the earth (other than the Sun) is Proxima Centauri. Its distance from the earth is 4.28 light years. This star is visible only in the Southern Hemisphere. The nearest star visible in the Northern Hemisphere is Sirius. Its distance from the earth is 8.8 light years. In addition to this, another neighbouring star is Alpha Centauri which is 4.37 light years away from us.
The farthest star from the earth which is visible with our naked eye is more than eight million light years away from us. If we use powerful telescopes, we can even see stars that are 1000 times more distant than this one. Some stars are so far away from the earth that light from them takes more than 1,000 million years to reach the earth.
Scientists have developed various kinds of optical and radio telescopes to study stars. They have gained considerable knowledge relating to the heavenly bodies with the help of these telescopes.