HR Diagram Activities

You should understand how the HR diagram can be used for the following:

  1. Plot nearby and bright stars and compare them.
  2. Plot stars in a young open cluster (eg Pleiades) and stars in a globular cluster and compare them. This introduces the concept of using an HR plot to infer the age of a cluster from zero-age main sequence fitting (ZAMS).
  3. Given a star's position on an HR diagram, determine its characteristics and what evolutionary stage it is at. You should be comfortable with the different quantities that can be used on each axis of the diagram.
  4. Show the evolutionary sequence of 1, 5 and 10 solar-mass stars on an HR diagram and be able to account for the different stages.

Currently, one activity is available on this site that addresses some of these requirements:

Other activities are being written and will be posted up here shortly.

There are numerous other excellent activities at other sites that address these points. Some are listed below:

  • Cluster Color-Magnitude Diagrams and the Age of Stars provides colour indices and magnitude data for the Pleiades and 47 Tuc, a globular cluster so that you can plot colour-magnitude diagrams and determine cluster ages.
  • HR Applet (© McGraw Hill) is an online applet showing stellar evolution on the HR diagram. You can specify a star's parameters and watch it evolve. An evolutionary track is plotted. The site has accompanying explanations and background information.
  • HR Diagram is an exercise that you can print out. It provides background theory and tables of bright and nearby stars for you to plot on the accompanying HR plot and frequency plot.
  • HR Diagram Simulator allows you to place 1, 10 or 100 stars on the main sequence then compare their evolution off the main sequence either in steps or as a movie. Useful for demonstrating the concept of ZAMS.
  • Properties of Stars allows to examine the properties of several stars using a virtual observatory then explore some of the evolutionary stages. An excellent activity with high quality graphics and sound pedagogy from University of New Mexico.
  • Star Clusters is another detailed activity from University of New Mexico where you find the distance to star clusters then use them to explore stellar evolution and the ages of stars. Excellent graphics and development of concepts. Useful for understanding the concept of ZAMS and spectroscopic parallax.
  • Stellar Evolution Applet , from Victoria University in Canada allows you to compare evolutionary tracks off the main sequence for stars of different masses and metallicities.
  • Stellar Evolution Simulation from Cornell allows you to alter the mass of a star and see how this affects its evolutionary track from the main sequence onwards. The results are plotted on a luminosity/temperature HR diagram in time steps with representations of star size. It comes with a useful set of instructions. Highly recommended.
  • Stellar Evolutionary Tracks is another Java applet.