The sun is a star with a 696,000-km radius. Its volume is so great it could fit 1.3 million earths inside it, and it is 330,000 times as heavy as our planet. Although our sun is so much larger than the earth, it is only of average size among the other stars in our galaxy. Its surface and core temperatures are 6,000 degrees Kelvin and 15,000,000 degrees Kelvin, respectively. How do you suppose our sun was born?

It is said the sun was born some 5 billion years ago. At that time, a giant star in our galaxy ended its life in a cataclysmic supernova explosion. The shockwaves from such an explosion would compress the surrounding gases that, as they cooled, formed a cloud containing a mixture of dust and hydrogen atoms and molecules. This cloud contracts over a long period of time under their own gravity, causing them to grow denser and heat up internally. Once their core reaches a sufficient temperature (about 10,000,000 degrees Kelvin), nuclear fusion begins, meaning that hydrogen atoms start fusing together to form helium. With the start of nuclear fusion, stars begin emitting massive amounts of energy, making them shine.

This is how the sun was born, and is also the reason why stars like the sun, which emit their own light, are immense masses of gas in which nuclear fusion is occurring at the core.