Write a note on Sun.

ANS:


* Sun is the center of our solar system.
* About 99% of the mass of the solar system is contained in Sun. It mainly consists of hydrogen and helium along with elements like carbon, oxygen, magnesium, nickel, cobalt, etc.
* It is the main source of energy for earth and other planets.
* It is a sphere of hot gases with surface temperature of about 6000 K.
* The 400 km thick, bright layer around the sun is known as 'photosphere'.
* The layer beyond photosphere is invisible normally because the gases are very hot and less dense. But during solar eclipse, it becomes visible like a "crown". This layer is known as 'Corona'.



* The temperature in the core region is about 1.5 crore (15 million) K. At this temperature, thermonuclear fusion process takes place in which four hydrogen nuclei fuse to form a nucleus of helium.
* During this process some mass is lost which is converted into energy as per Einstein's mass-energy equation E = Δmc2, where Δm is the lost mass and c is the speed of light in vacuum.
* The mass of sun is 1.99 x 1030 kg. This mass is called 'Solar Mass' (M0).