Expert: James Gort - 1/20/2009

Question
 Hello Mr. Gort, thanks for making yourself available.  I teach art in Philadelphia.  Our sun appears yellow but is in fact (I guess?) white light as a prism breaks it down into a full color spectrum.  Would a planet with a blue sun or a red sun also be in fact white light?  Would rainbows appear the same, all other factors being equal?

Answer
Hello Lauren,

Yes, our sun is indeed yellow, but not "very' yellow.  Its light is comprised of all the colors in the spectrum (including infrared and ultraviolet, which we can't see, and some of the light is filtered out by our atmosphere), but there is slightly more radiation in certain colors.  In our sun, there are chemical elements in the atmosphere which burn in certain colors.  Our sun is yellow mainly because of sodium in its atmosphere, which burns brightly in the yellow part of the spectrum. So the sun emits slightly more radiation in the yellow part than the other parts, although all colors are represented.  If the colors were all "exactly" in the right proportion, the sun would appear white.  There are no really "white" stars, although some are pretty close.  The hottest stars are generally blu-ish, while the coolest stars are red-ish.  Our sun is a medium star, making it yellow-ish.

Hope that helps.

Prof. James Gort