HRdiagrammets

The Hertzsprung-Russell diagram, often abbreviated as H-R diagram or HR diagram, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their spectral types or effective temperatures. It was introduced in 1911 by Ejnar Hertzsprung and Henry Norris Russell, two of the most prominent astronomers of the early 20th century. The diagram is a fundamental tool in the study of stellar evolution, as it allows astronomers to compare the properties of stars and understand their life cycles.

The H-R diagram is typically plotted with the spectral type or effective temperature on the horizontal axis and the absolute magnitude or luminosity on the vertical axis. This arrangement allows for the classification of stars into different groups based on their properties. The main sequence, a diagonal band running from the upper left to the lower right of the diagram, is where the majority of stars, including the Sun, spend the majority of their lives. Above and below the main sequence are giant and supergiant stars, as well as white dwarfs, which are the remnants of stars that have exhausted their nuclear fuel.

The H-R diagram is also used to study the evolution of stars, as they move through different regions of the diagram as they age. For example, a star will move from the main sequence to the giant branch as it exhausts its core hydrogen and begins to fuse hydrogen in a shell around the core. The diagram is a powerful tool for understanding the life cycles of stars and the processes that govern their evolution.