A nebula is a large cloud of gases and dust in outer space. There are two types of nebulae – diffuse nebulae and planetary nebulae. Diffuse nebulae are much larger than planetary nebulae. Some times a diffuse nebula is close enough to a star so that its dust reflects the light. A planetary nebula is an expanding cloud of glowing gas that surrounds a star.
If we look at the sky at night through a telescope, we can see many big black and white spots. These spots are called nebulae. The word ‘nebula’ comes from Latin which means ‘mist’ or cloud as they give the appearance of mist to us.
Black spots are called ‘black nebulae’, whereas white ones are called ‘bright nebulae’. In reality these nebulae consist of dust, gas and a cluster of stars. Many nebulae are situated in our Milky Way, but many more are outside it. Lot of information has been obtained about them with the help of powerful telescopes.
There are some 2000 nebulae in our Milky Way. It is estimated that there are millions of them existing outside it. Some of them are elliptical, some others are spiral shaped and some do not have any regular shape at all.
The temperature of the nebulae has been found to be varying from 6,000°C to 12,000°C. The temperature of the black nebulae is much less than that of the bright ones. Therefore, they appear black. They contain mostly hydrogen and helium gases. The nearest nebula is 300 light years away from us. And those situated outside the Milky Way are at least 150,000 light years away from us.
Scientists have photographed some of the nebulae. The photograph of the Crab nebula indicates that it is some 6000 light years away from earth. The photograph of one nebula resembles the head of a horse. It is, therefore, named the ‘Horse’ nebula. Another appears like a ring and thus it is called ‘Ring’ nebula. Nebulae are classified depending on whether they emit, reflect or absorb light. Scientists have already studied many nebulae.
