SOLAR SYSTEM

Detailed explanation-1: -Stars begin to form from clouds of gas in space. The cold temperatures and high densities (compared to elsewhere in space, but would be considered a vacuum on Earth) of these clouds allow gravity to overcome thermal pressure and start the gravitational collapse that will form a star.

Detailed explanation-2: -Even though the protostar has a surface temperature only about half that of the Sun, it is hundreds of times larger, making its total luminosity very large indeed-in fact, much greater than the luminosity of most main-sequence stars.

Detailed explanation-3: -The center of the protostar, which is becoming hotter and denser with time, eventually reaches the point where it is so hot and so dense, hydrogen nuclei start to fuse together to form helium nuclei.

Detailed explanation-4: -Reaching the Main Sequence… As it contracts, the protostar gets smaller, hotter and denser. This means that a star in the protostellar stage is cooler (redder) and bigger than it will be in the Main Sequence stage (the hydrogen-fusing stage).