Caption: A Hertzsprung-Russell (HR) diagram for a large sample of stars. The sample is NOT a large volume-limited one, and so does NOT give the true distribution of stars among the stellar classifications (i.e., spectral type and luminosity classes).

Features:

1. In this version of an HR diagram, luminosity (in units of solar luminosity) on the left and absolute magnitude on the right are plotted versus color index (AKA color) B-V on the bottom and spectral type and stellar photosphere temperature on the top.

   The high-temperature blue-white stars are on the left and the low-temperature red stars on the right.

2. The HR diagram is a plot of 22000 stars from the Hipparcos Catalogue plus 1000 low-luminosity stars (red dwarfs and white dwarf) from the Gliese Catalogue of Nearby Stars. Since there ar actually far more low-luminosity stars than high-luminosity low-luminosity stars, the sample is biased toward more luminous and, thus, more massive stars.

   So the stars on the plot do NOT reflect the actual relative abundances of stars of each stellar classification as noted in the preamble. If it did show the correct relative abundances, there would be far more stars at the lower end of the main sequence.

   Nevertheless, the sample is sufficiently fair that it shows there are relatively few bright giants (luminosity class II) and supergiants (luminosity class I). Though relatively rare such stars are rather conspicuous because of their high luminosity.

3. Below are Table: Luminosity Classes and and the Main-sequence rule:

4. Note that white dwarfs are the compact remnants of stars that on the main sequence had less than about 8 M_☉. They have NO nuclear burning and on the time scale of gigayears cool slowly moving towards the bottom-right of the HR diagram.