The Sun

The Sun is one of more than 100 billion stars in the giant spiral galaxy called the Milky Way. The Sun is the centre of the Solar System. Its mass is about 740 times as much as that of all the planets combined. The sun is about 150 million km away from the earth.

The huge mass of the Sun creates the gravitation (pulling force) that keeps the other objects travelling around it in an orderly manner. Modern estimates place the Sun at a distance of about 32,000 light years from the centre of the galaxy.

The Sun continuously gives energy in several forms - visible light, invisible infra-red, ultraviolet, X-rays and gamma rays, cosmic rays, radio waves and plasma.

The Sun and the neighboring stars generally move in almost circular orbits around the galactic centre at an average speed of about 250 km per second. The Sun at this rate takes 250 million years to complete one revolution round the centre. This period is called a Cosmic Year.

Red Giant

Like all other stars, the Sun is composed mainly of hydrogen. Its energy is generated by nuclear collisions in its interior. It is calculated that the Sun consumes about a trillion pounds of hydrogen every second.

At this rate, it is expected to burnt out its stock of hydrogen in about 5 billion years and turn into a Red Giant. When the Sun turns into a Red Giant, it would have swelled a hundred times in diameter and increased a thousand times in brightness - bright red. It will then occupy about 25 percent of the horizon.

The nearest planets, Mercury and Venus, would melt. The oceans of the earth would evaporate and disappear. The earth would remain a barren rock, heated to melting point of lead. All life on earth would cease. The Sun will survive as a Red Giant, for about a hundred million years more, slowly dissipating its enlarged outer shell leaving a tiny core. This core will be a faint, white dwarf sun no larger than the present planet Mars.

Structure of the Sun

The glowing surface of the Sun is called Photosphere. Above the photosphere, is the Chromosphere, so called because of its reddish colour. Beyond this layer (chromosphere) is the magnificent Corona of the Sun which is visible during eclipses only, as a remarkable silver pearly radiant glow around the Sun.

At the core of the Sun where thermonuclear reactions take place the temperature level is around 15 million degrees K, The density of the core is estimated at a hundred times that of water.