Heat, Radiation, and the Temperatures of Stars

Abstract

We have reached a stage in our study of stars at which we can begin to deduce the numerical values of important surface and internal stellar characteristics that we cannot measure directly. Among these characteristics, whose numerical values we can calculate by applying the known laws of physics to stellar data, is the surface temperature of a star. Like the sun, all the stars around us are hot, self-luminous bodies. But just how hot are the stars and how do we measure their surface temperatures, which are measures of their hotness? In our discussion of the sun we gave its surface temperature as about 6000°K. How did we obtain this value and can we apply the same procedure to determine the temperatures of stars in general? The answer is yes to the last part of the question and we can answer the first part once we understand the meaning of temperature and the nature of stellar radiation.

Bright star, would I were steadfast as thou art—

Not in lone splendor hung aloft the night

And watching, with eternal lids apart,

Like Nature’s patient, sleepless Eremite,

The moving waters at their priest-like task

Of pure ablution round earth’s human shores.

—JOHN KEATS, Bright Star