# Star colors?

1. Aug 13, 2004

### Tree Penguin

Hi, i read something about light turning red due leaving gravitational fields.
A long time ago i played a game called ascendancy which was about colonizing solarsystems and battling other species and they had a few different kinds of stars in it, a few of these where white and blue dwarfs and red giants. First of all, is that right in real life? And if so, is the reason for the colors the composition of gasses of the sun or the gravitational field?

n00b so don't be rough on me , please do correct me whenever i said something stupid .

2. Aug 13, 2004

### Janus

Staff Emeritus
Yes, the stars you listed are real star types. The color of a star is due to its temperature. Cooler stars are red and hotter stars are blue/white. Our own sun is a yellow dwarf.

3. Aug 13, 2004

### Nereid

Staff Emeritus
Light doesn't 'turn red leaving a gravitational field', it gets redshifted as it moves away from a massive object; this is called the 'gravitational redshift'. 'Redshift' simply means that the perceived wavelength is longer (redder) than it would be if there were no massive object. It's a prediction of Einstein's theory of General Relativity (GR), and has been observed in experiments here on Earth and also out in space (e.g. near giant black holes at the centre of galaxies). However, so far as our eyes are concerned, the gravitational redshift is far too small to notice - for anything that we can see in the sky.

4. Aug 13, 2004

### chroot

Staff Emeritus
To add to Nereid's post, I should mention that neither cosmological redshift (due to the expansion of the universe) nor gravitational redshift (due to the energy required for light to climb away from a massive body) are important for the coloring of stars.

Stars are different colors simply because they are different temperatures, just as a white-hot poker is hotter than a red-hot poker. The color is really just an indication of surface temperature. The reason different stars have different surface temperatures is that they have different masses, ages, and/or compositions. In general, very massive (adult) stars have higher surface temperatures and appear blue or white, while low mass (adult) stars have lower surface temperatures and appear orange or yellow.

As stars age, however, many go through a period in which they grow larger and externally cooler, and are called "red giants."

- Warren

5. Aug 13, 2004

$${\lambda_p}{T} =$$2.9 * 10^-3 m\K