HOW SUN PRODUCE HEAT

 The core of the sun is so hot and there is so much pressure, nuclear fusion takes place: hydrogen is changed to helium. Nuclear fusion creates heat and photons (light).

The sun's surface is about 6,000 Kelvin, which is 10,340 degrees Fahrenheit (5,726 degrees Celsius). The amount of solar heat and light is enough to light up Earth's days and keep our planet warm enough to support life.

Astronomers estimate that the Sun's luminosity will increase by about 6% every billion years. This increase might seem slight, but it will render Earth inhospitable to life in about 1.1 billion years. The planet will be too hot to support life.

Sun is a vast source of energy. From sun we are getting a lot of energy by using solar panels. 

If there is no sun, there is no man in the world.