I. Introduction Astronomers have developed highly sophisticated mathematical models of stellar evolution which predict the change in stellar properties as stars of differing masses age. These models predict the photospheric temperature and luminosity of stars, and therefore their position on the H-R diagram, as they age. How do astronomers check their mathematical models of stellar structure and evolution? The method that astronomers use for checking models of stellar evolution is somewhat akin to the botanist who walks into the forest to study the evolution of the redwood tree. It practical isn’t for a biologist to watch a tree grow from a seedling to a giant adult redwood. In the forest one may see redwood seedlings, young saplings, young adult redwoods, mature redwoods, and decaying logs. From this a complete picture can be inferred of the biological evolution of the redwood, from seed to decaying log. Similarly, the astronomer must piece together the complicated picture of the life cycle of a star from the measured properties of the vast numbers of stars seen in the sky. This is done by assuming that stellar properties are a function of a star’s mass, composition, and age. Current theories of stellar evolution are not perfect, but they explain most of the stellar properties that we can measure. The tempo of a evolution is tied to star’s its mass. The more massive a star is, the faster it evolves through all phases of its life cycle.
I. Introduction Astronomers have developed highly sophisticated mathematical models of stellar evolution which predict the change in stellar properties as stars of differing masses age. These models predict the photospheric temperature and luminosity of stars, and therefore their position on the H-R diagram, as they age. How do astronomers check their mathematical models of stellar structure and evolution? The method that astronomers use for checking models of stellar evolution is somewhat akin to the botanist who walks into the forest to study the evolution of the redwood tree. It isn’t practical for a biologist to watch a tree grow from a seedling to a giant adult redwood. In the forest one may see redwood seedlings, young saplings, young adult redwoods, mature redwoods, and decaying logs. From this a complete picture can be inferred of the biological evolution of the redwood, from seed to decaying log. Similarly, the astronomer must piece together the complicated picture of the life cycle of a star from the measured properties of the vast numbers of stars seen in the sky. This is done by assuming that stellar properties are a function of a star’s mass, composition, and age. Current theories of stellar evolution are not perfect, but they explain most of the stellar properties that we can measure. The tempo of a star’s evolution is tied to its mass. The more massive a star is, the faster it evolves through all phases of its life cycle.