01 Sep—Sun

Just like all of the stars that came before it, our Sun began its life as a cloud of interstellar gas and dust.

The gravity of the atoms in the gas cloud — mainly hydrogen and helium — tried to pull the cloud together, but the faint pressure of the cloud prevented its collapse.

Then shock waves from our mother star's supernova disturbed this balance. They spread through the cloud creating eddies and pockets of denser gas in their wake. In the part of the cloud that would become our Sun, one of these slightly denser eddies began to collapse and spin. The shock waves had packed the atoms closely enough that gravity could overcome the pressure in the cloud.

In a now familiar dance, as the cloud contracted, it began spinning faster. In the center of this swirling cloud, the beginnings of of a star (a protostar) took shape and began to heat up as its atoms collided with each other.

Sun—1 September

When the protostar grew hot enough, it began to fuse its hydrogen into helium, becoming a fully fledged star about 4,570 million years ago. The energy released by these fusion reactions balanced the gravity of the star, its gravitational collapse halted, and our Sun became stable.

A disk of gas and dust that would soon become the planets of our solar system began forming around our newly born Sun.