View Single Post
Mar24-10, 03:30 PM
Sci Advisor
HW Helper
tiny-tim's Avatar
P: 26,148
Quote Quote by ABHoT View Post
Does light only come from matter? The difference between a light bulb switched on and off is just temperature (or electricity?) If a star wasn't 'on fire' would it give off any light?
A star with no nuclear fuel left would give off light according to its temperature (same as a planet does).

Basically, everything gives off a range of light according to its temperature (google "black body radiation").

eg red stars are cooler than blue stars.

A light bulb gives off light because it is hot.

In addition, some things give off light at certain exact frequencies because their molecules are vibrating (eg sodium lamps).
I am wondering where the energy is going. Emitting light must cost the matter its energy(?), but being hit by light doesn't give you any so where is it going?
No, being hit by light does give you both energy and momentum.