These are the notes for the class taught on September 15, 2021:
And this a video recording of today's class:
Class of September 15, 2021
An observational Hertzsprung–Russell diagram with 22,000 stars plotted from the and 1,000 from the of nearby stars. Stars tend to fall only into certain regions of the diagram. The most prominent is the diagonal, going from the upper-left (hot and bright) to the lower-right (cooler and less bright), called the . In the lower-left is where are found, and above the main sequence are the , and . The is found on the main sequence at luminosity 1 ( 4.8) and B−V 0.66 (temperature 5780 K, G2V).
Credit Richard Powell and wikipedia.