• THE STARS:

Introduction:
Stars are those heavily body which produce energy by nuclear reactions. They are held in a stable state by balancing the outward radiation pressure by the inward gravitational force.

Characteristics of Stars:
Stars are self-luminous bodies, situated at great distance from the solar system.
They do not revolve round the sun.
They have their own light.
The sun is our nearest star while the next nearest star is Proximal Centauri, which is at a distance of about 40 million km from the earth.
The size of the stars varies considerably from super-giant stars, which are several hundred times larger than the sun, to dwarf stars that are much smaller than the earth.

Classification of Stars:
The popular method of classification of stars is stellar classification. According to this classification, the color of a star gives an indication of its temperature. So stars are classed according to their spectra in sequence of decreasing temperature. The types of stars according to the Henry Draper Stellar classification are.
Type O, B, A, F, G, K, M.

Kinds of Stars:
There are four kinds of stars, which are as under: -

1. Fixed Star: - Fixed Stars are those stars, which do not change their position in the sky. These are fixed and are known as dog stars.

2. Binary Stars: - Binary stars are those stars, which are in group of two stars. They revolve round a common center under mutual gravitational attraction.

3. Temporary Stars: - Temporary stars are those stars, which suddenly flare up with great brightness and fade away after a short time. They are also called Nova.

4. Variable Stars: - Variable stars are those stars whose brightness varies from time to time.