WHAT IS THE SUN?
The sun is a medium-sized star. It is a ball made up of hot gases-mostly hydrogen. It is very; very big in size having a diameter of 1392 thousand kilometers 1100 times the diameter of the Earth. So, its volume is over a million times the volume of the earth. It has a surface temperature of about 6000°C. But at its center the temperature is about 15 million °C because nuclear reactions are always going on there. These reactions keep the sun shining and it emits light and heat in all directions.
The sun was born about 4500 million years ago out of the huge dark gas cloud in one of the arms of the Milky Way. Several other stars like the sun might have been formed at that time. But we cannot see them as they are far, far away from us. Our sun is the nearest star to our earth.
The sun has been losing its energy in the forms of heat and light. It has been through nearly half its life and the energy left with it is enough to keep it shining steadily for another 5000 million years.
Compared to other stars, the sun is smaller and dimmer. But as it is only 150 million kilometers away from us, it looks large and bright. Only a small part of the sun's energy reaches our earth. It is due to this energy that the earth is a livable planet, with various living things on it.
The sun is roughly round in shape and has spots on it. These areas are comparatively cooler than other areas. So, they look like spots on the face of the sun. They are called sunspots.
Huge streamers of glowing gas leap up from the sun's surface. They are like flames and are called prominences. Some of them curve to make arcs of fire. Moreover, atomic particles shoot in all directions from the sun at the speed of a bullet. They spread out very thinly. They are called solar wind, which blows even beyond Neptune.
The sun has three layers:
1. Photosphere: The shining surface that we see from the earth
2. Chromosphere: A layer some thousand km. below the photosphere
3. Corona: The atmosphere that stretches millions of kilometers around it
