But light can also be absorbed by electrons, the electromagnetic energy can be turned into kinetic energy of the electron to make it jiggle up and down. So electrons can exchange energy with the photons. If the material is very dense then the photons get continually absorbed and re-emitted, absorbed and re-emitted and their energy comes into equilibrium with the energy of the electrons (which is determined by the temperature of the material). See also properties of light. So the photons we see from dense, hot material have energy which is characteristic of the temperature of the material and NOT determined by the material itself e.g. a coal (carbon) fire glows red hot and so do the metal wires which form the heating element of an electric fire. The photon energy can be seen most easily by plotting a spectrum - the intensity of light at a given wavelength versus its wavelength. Where the electrons and photons are in equilibrium the photons have a very characteristic spectral shape called (somewhat confusingly) a Blackbody (continuous) Radiation. This is very very important in astrophysics because all we have is the light - we cannot go there with a thermometer! Yet this says that if we are looking at something where the photons and electrons haev interacted many times and come into equilibrium then we can measure the spectrum of the light, and then know the temperature of the star.
So back to stars:
Pages 102-105 in Kuhn
Pages 347-355 in Kuhn
The interior or the Sun
.
Neutrinos
.
an introduction to
the solar neutrino problem
.
everything about the
Solar neutrino problem
- browse through the popular level articles