HR diagrams are extremely important to astronomers. They can help to determine how a star will evolve over its lifetime and also how it will be classified based on its brightness and temperature. A star first becomes bright enough to be visible once it crosses the birth line, drawn in (color). It will then travel along its evolutionary track. If it becomes a asymptotic giant star it will travel through the asymptotic giant branch star area, and if it becomes a variable star it will travel in the instability strip. A star the size of the sun would have an evolutionary track similar to this one below, starting out as a gaseous cloud and ending its life as a white dwarf.