Comparing stars
Comparing stars

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Comparing stars

3 Summary

3.1 The H-R diagram

  • The Hertzsprung-Russell (H-R) diagram displays the photospheric temperatures and luminosities of the stars. The corresponding radii are obtained from Equation A. The H-R diagram is a very useful aid to our understanding of the stars and their evolution.

  • The stars tend to concentrate into certain regions of the H-R diagram, and so some combinations of temperature and luminosity occur far more commonly than others. These concentrations define various classes of stars, the main classes being main sequence stars (about 90% of observed stars), red giants, supergiants, and white dwarfs.

  • We can explain the concentrations on the H-R diagram as places where stars spend comparatively large fractions of their lives, the main sequence phase accounting for the largest fraction.

  • Different types of variable stars help our understanding of stellar evolution. The supergiant phase ends in a Type II supernova - a huge explosion that destroys the star. The T Tauri stars (one type of irregular variable) seem to be on the threshold of joining the main sequence, approaching it from above on the H-R diagram. Regular variables, such as the Cepheids, give us clues about some of the processes that are of importance in stellar evolution. The novae (another type of irregular variable) help us to understand disturbances to the normal course of evolution that occur in binary systems, and this aids our understanding of the normal course itself.

S282_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus