Question:Describe the life cycle of a small star, such as the Sun.
All stars start as a Nebula.
A nebula is a huge cloud of dust and gas in space.
The original nebulae where only gas, dust came later from the explosions of older stars.
The nebula that our star formed from must have been the remnants of a previous star that had exploded. We know this becasue the heavier elements must have been created in a previous star since they did not exist after the Big Bang.
Over time Gravity causes the nebula to contract to become a Proto-star.
As the Protostar is compressed by Gravity it becomes hotter and hotter.
Eventually the core of the star becomes hot enough for thermonuclear Fusion to begin, which is called 'Ignition'.
After 'Ignition' the star becomes even hotter and begins to shine.
This is the 'Main Sequence' stage of the stars lifecycle.
Stars remain in the 'Main Sequence' for most of the lifetimes.On the diagram, each image of the Sun represents the appearance of the Sun after equal time intervals.
What happens next depends upon the 'Mass of the Star'.