hard level astronomy

Question 1

The Solar Nebula Theory

Answer 1

1. Stars begin in a cloud of gas composed of hydrogen, helium, and dust, called a nebula.
2. Gravity pulls the parts of the nebula together so they spin.
3. As the nebula starts to rotate, hydrogen drifts to the centre, heats up, and compresses; a protostar.
4. When the temperature at the centre reaches 10 million degrees, fusion begins; the star “turns on”.
5. A solar system is formed from the cool dusty material on the outside of the nebula.