The Main Sequence and the HR Diagram

Nino Chelidze, Idaho State University

The Hertzsprung - Russell diagram is a graph created by Ejnar Hertzsprung and Henry Norris Russell in 1911-1913. Astronomers use it to classify stars according to their luminosity, spectral type, color, temperature and evolutionary stage. There are three very different types of stars; therefore the HR Diagram has three main regions. Stars are born, undergo evolutionary stages, reach the stable phase of hydrogen burning and stay in this stage for most of their lifetime. Stable stars lie along the Main Sequence according to their mass. After billions of years stars die. Evolution stages, spectral classification and properties of main sequence stars will be discussed.