I learned quite a bit from the H-R diagram. I chose the star Bellatrix, and for starters, I never even knew a star named Bellatrix even existed. I can see that my star is about 30,000 K. 30,000 K means it roughly 5 times hotter than the sun. I know that Bellatrix is spectral type B by looking at the bottom of H-R diagram. Spectral type B's are a light shade of blue. The luminosity of Bellatrix is 10 to the 4th power which means how much brighter it is from the sun. Bellatrix's temperature is 4 times hotter than the sun (8,000 K). Since Bellatrix has hydrogen, helium, and helium ions I know that Bellatrix also has these. All stars that have the same spectral type have the same composition. The mass of Bellatrix is 10 times as much as the sun.
