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Formation of the Sun


The Sun

Nearly all of the mass in our Solar System is in the Sun. The Sun is very large. Its diameter is over 100 times the Earth's. 

The Sun is the source of nearly all the energy we receive. For many years, it was a mystery as to where this came from, and this baffled the leading scientists. 

It is now understood that the nuclear fusion is the energy source.

 In nuclear fusion hydrogen nuclei are joined together to make helium nuclei. This releases enormous amounts of energy.

Nuclear fusion

Nuclear fusion involves two atomic nuclei joining to make a large nucleus. Energy is released when this happens.

The Sun and other stars use nuclear fusion to release energy. The sequence of nuclear fusion reactions in a star is complex - but, in general, hydrogen nuclei join to form helium nuclei. Here is one nuclear fusion reaction that takes place

hydrogen nucleus + hydrogen nucleus   →   helium nuclei   


In stars larger than our Sun helium nuclei can be fused together to create larger atomic nuclei. As the Earth contains many of these larger atoms, 

like carbon, oxygen, iron, etc, scientists believe that our Solar System was made from the remains of an earlier star.

YouTube Video

Stars form when  massive clouds of dust, gas and other matters in space which is called Nebula clump together because of gravitational forces. Nuclear reactions release energy to keep the star hot.

 Planets form when smaller amounts of dust and gas clump together because of gravitational forces.


Formation of a star

Stars form from massive clouds of dust and gas in space (nebula). The animation summarises how this happens.

Gravity pulls the dust and gas together.

Stars form from massive clouds of dust and gas in space

As the gas falls together, it gets hot. A star forms when it is hot enough for nuclear reactions to start.

This releases energy, and keeps the star hot.

Gravity pulls the dust and gas together

During its 'main sequence' period of its life cycle, a star is stable because the forces in it are balanced.. 

Our Sun is at this stable phase in its life.

The Sun is halfway through its 10 billion year stable phase

Gravity pulls smaller amounts of dust and gas together, which form planets in orbit around the star.