Introductory Astronomy: Stellar Evolution

Stars are not unchanging objects; as they age, they change, going through a sequence of phases, and eventually "die". In each phase, their outside appearance as well as their interior structure is different. Each phase of a star's life has a different name, such as "Giant" or "Main Sequence". The phases a star will go through, as well as the amount of time it spends in each phase and the final state of the star, are determined by the star's mass when it is a Main Sequence star.

It is really important to understand that, as a star is aging, its interior is changing. This is what makes the star go through different phases. These internal changes affect the star's temperature and luminosity and therefore determine where a star will be graphed on an HR diagram (like the one above). During its life, a star may be graphed at several different locations on the HR diagram (one location per phase it goes through!) without ever moving physically in space. Therefore, movement on the HR diagram just means the inside of a star is changing, NOT that the star itself has moved.

To learn more about the evolution of a certain star, click below on the mass range you are interested in. (Note that the sun would be considered a mid mass star.)

Evolution of Main Sequence Stars

After you review these sections, try a few sample questions to test your understanding. These questions are typical of questions given in introductory astronomy course exams. They are meant only to give you an idea of what kinds of questions MIGHT be on your exam. Just because these questions are here does NOT mean that you will have questions like them on your exam, NOR does it even mean that you will have questions on these topics on your exam. They are just PRACTICE questions for this topic!