The Hertzsprung-Russell (H-R) Diagram

The Four Factors In The H-R Diagram

The H-R diagram can be interpreted by analyzing the four factors that can make up the axis labels. These four factors are temperature, luminosity, absolute magnitude, and spectral class.

  1. Temperature: Temperature is measured in degrees Kelvin. On this scale, the temperature of stars can range from around 3,000 K to about 40,000 K. Cooler stars include older main sequence stars and giants. Hotter stars include white dwarfs and younger main sequence stars.
  2. Absolute Magnitude: Absolute magnitude is how bright an object is. Large stars, like super giants and giants, have very low absolute magnitudes, while older main sequence stars, like Betelgeuse, have high absolute magnitudes.
  3. Luminosity: Luminosity is the amount of radiation a star gives off in a certain time. Younger main sequence stars, giants, and supergiants have a high luminosity, while white dwarfs have a low luminosity.
  4. Spectral Class: The spectral classes are divided into seven different categories. Each star's spectral class has a color.

Observe how the H-R diagram looks when star color is added to it. Remember that the hottest stars are blue in color and the coolest stars are red. Main sequence stars are classified in seven different spectral classes: O, B, A, F, G, K, M. Main sequence stars are stars that vary from each other by color, temperature, and luminosity. The most popular main sequence star is our Sun, and it is in the spectral class G. Generally, younger main sequence stars are bluish in color, and as they age they become yellow and then red. This is also an indication of the temperature at which they burn. Blue stars are very hot, while red stars are very cool.

Hertzsprung-Russell diagramThe Hertzsprung-Russel diagram provides unique insight into the composition and life of stars. In this interactivity, read the introduction and then explore the H-R diagram. Click on each of the spinning dots to learn about the different areas on the diagram. Click the player to begin.

Download a printable version of the interactivity above.