Evolution, Page 28: [Next Page] [Class Home Page] Textbook pages 321 - 344

The Hertzsprung - Russell Diagram

80 years ago, We knew nothing of how the Sun or stars worked. Research at that time merely plotted stellar properties against each other, looking for possible patterns.

What properties of stars were known at that time?

• Spectral Classification.

• Relative Brightness.

But-- if they knew distance (via parallax), they knew LUMINOSITY.

For most stars, spectral types (essentially temperature) and LUMINOSITY (=Absolute Magnitude), were found to be related in a very unique way:




This diagram was to be known as, The Hertzsprung-Russell (H-R) Diagram, named after the astronomers who discovered this relationship.