Hertzsprung-Russell Diagram

From Slackerpedia Galactica

The Hertzsprung-Russell Diagram (commonly referred to the "HR Diagram"), pioneered independently by Elnar Hertzsprung and Henry Norris Russell, plots luminosity (or absolute magnitude or apparent magnitude) as a function of temperature (or color or spectral type) for stars. It's usefullness comes from how it illustrates stellar evolution of many different types of stars in one glance.

It is a diagram that anyone who takes Astronomy 101 has come to love, fear or both. But it's quite remarkable in how it essentially creates a graphical way to represent the complexities of stellar evolution in one simple plot.

The original H-R Diagram plotted the absolute magnitude of stars (which is directly related to their optical luminosity) versus their spectral type (which to great degree reflects their temperatures). Luminosity and absolute magnitude and spectral type and temperature are derived parameters, and to some extent theoretical because they require additional (and not always well-defined) information to derive. A purely observational Hertzsprung-Russell Diagram which compares apparent magnitude against a photometric color is known as a Color-Magnitude Diagram.

The Earth's Sun (Sol) is spectral class G2V with a temperature a little under 5800 K, and its luminosity is (wait for it...) one solar luminosity. It will be left as an exercise to the reader to find it in the graph to the right.