The Origin of the Earth

The Evolutionary Cycle of Stars

The key features of stars which are of interest to astronomers are their mass, their luminosity, their surface temperature and the distance they are away from us. These parameters are used to classify stars into types. More importantly they are also used to place stars into an evolutionary sequence which describes their formation, life and death. A widely used classification diagram for stars is the Hertzsprung-Russell Diagram (the H-R diagram) which is a plot of luminosity vs effective surface temperature. The luminosity of a star is a function of its radius and effective temperature. (for more details see

The Hertzsprung-Russell diagram.

The Hertzsprung-Russell Diagram shows four main groupings of stars. These are the:

The cycle of birth-life-death for a star may be charted on a Hertzsprung-Russell diagram.

The life cycle of a star on the Hertzsprung-Russell diagram.

Most stars evolve onto the Main Trend and then into the Dwarf stage as follows:

Further details of the process of star formation may be found on the following web sites: