Sun Aug 31, 2003 12:40 pm by Tawakalna
i don't do astronomy although i learnt star names and constellations for navigation. i did find out about this light business though in one of those guides to everything scientific, you know, fusion reactors for beginners and all that stuff (thats a lie i did already know this)
all "live" stars that is stars actively undergoing a nuclear process generate electro-magnetic (EM) radiation which distantly we percieve as light, or in the case of the sun heat too. obv. there a lot of other em radiations but lets concentrate on the subject in hand, besides most of the other wavelengths are too weak at stellar distance to be easily percieved, you need special kit to do that.
the part of the EM spectrum that manifests itself to us as visible light is known collectively as "white light" of course it isn't white at all. we see colour because of the absorption of certain wavelengths by the chemical composition of whatever we are looking at, which is then interpreted by our brains as "colour"
As colour is determined by chemical composition you can use this attribute to work out the composition of stars and other stuff using mass spectrometers. All stars work on the same principle but their chemical compositions can vary wildly hence we see different coloured stars, even though they all give off "white" light and everything else like IR, UV, gamma, x-ray, cosmic etc.
a stars composition depends upon the particular conditions of its origin and what elements went into it, what mass it is and how old it is. small white stars are usually younger and hotter, large red stars are usually older and cooler. this isn't always the case but it applies to "main sequence" stars which generally follow the same predictable cycles throughout their lives.
stars convert hydrogen to helium through fusion at high temperatures caused by gravity and pressure. As the star uses up its hydrogen it will eventually start to burn the helium, as this fuel is used up it is converted into other elements like carbon and iron. as the star changes its basic fuel it dramatically changes size and shape (the nova/supernova phenomena) but ultimately most stars end up a lump of dead ash with no nuclear activity, just a gravity well and a dense remnant of core. if the star was a large enough star this contraction wont cease at the core, the star will contract into a singularity with an event horizon i.e. black hole.
a star may have a doppler shift of red or blue depending upon its path and speed relative to us, but this is separate to its actual colouring due to its composition and temperature.
so in short, the wavelength of the light determines the colours we percieve, and the wavelength is determined by the composition of the star and its temperature.
addendum: the earth's atmosphere has some effect on the stars colour as far as observation goes in that atmosphere filters out higher wavelengths and therefore thats why the sun is redder at dawn and in the evening. it also causes the twinkle
Edited by - Tawakalna on 31-08-2003 13:44:03
Edited by - Tawakalna on 31-08-2003 13:45:49
Edited by - Tawakalna on 31-08-2003 16:53:34
