Color and the hr diagram

A star's color depends on its surface temperature. Just as an iron bar heated in a furnace glows first red, then yellow, then white hot, so the amount of energy heating each region of a star's surface controls its color. However, stellar size can vary, and if a star grows larger at a certain phase of its life cycle, its surface area increases, and the amount of energy heating each region of the surface falls. So a star can grow larger and cooler at the same time. By plotting the relationships between luminosity and color (or more accurately, spectral type) on a graph called the Hertzsprung— Russell diagram, astronomers have discovered rules that allow them to estimate the true brightness of a star.

0 0

Post a comment