Stars
A star is a mass of expanding gases. It is a self luminous heavenly body, as it is composed of a hot glowing gaseous mass having an intensely high temperature. Stars appear to twinkle, as they lie at great distances and moving layers of air scatter the sunlight. Like the Sun and the Moon, the stars appear to rise in the east and set in the west, because the Earth rotates from west to west.
Most stars, including the sun, are ‘main sequence stars’. They are fuelled by nuclear fusion converting hydrogen into helium. For these stars, the hotter they are, the brighter. These stars are in the most stable part of their existence and this stage generally lasts for about 5 billion years.
As stars begin to die, they become ‘giants’ and ‘supergiants’, bigger than the main sequence stars. These stars have exhausted their hydrogen supply and have become very old. Their cores contract as the outer layers expand. Eventually, these stars will explode and become planetary nebula or supernova, depending on their mass and then, depending on their mass, become white dwarfs, neutron stars, or black holes.
Smaller stars, like our Sun, eventually become faint ‘white dwarfs’, smaller than the main sequence stars. They are hot, white, dim stars. These hot, shrinking stars have completely exhausted their nuclear fuels and will eventually become cold, dark, black dwarfs.
The Sun is the star nearest to the Earth, only about 150 million kilometers away from us.
