Quote:
|
Originally Posted by kebo
just as a side note, a "twinkling" star (you know, the ones that seem to change colors) can sometimes be attributed to the motion of the star causing what is known as the doppler effect. As a star moves towards the earth, the light waves are compressed and the color is shifted toward blue. As it is moving away, the opposite happens and the colors shift toward red. This google has lots of cool info about the doppler effect.
kevin |
Twinkling is caused by our atmosphere. The doppler effect would not be noticed because it is not (usually) changing very quickly. It is also extremely small for most stars visible to the naked eye, and requires special equipment to measure. It is recognized by looking at the shift in spectral lines.
C4, the simple picture of electrons jumping energy levels is really only applicable to diffuse gases. Things get much more complicated once the densities get high enough that the different atoms start interacting with each other. The system then acts more like a bunch of charged particles attached to each other with springs (very roughly of course). Quantizing spring-mass systems gives just the right energy levels to get a continuum of radiation in the limit that the number of particles is very large (as it is in any macroscopic object). It may sound counterintuitive that you can get a continuum of radiation with quantized energy levels, yet it turns out that if you try to use the classical theory, you get an infinite amount of radiation! This was one of the things that originally motivated the development of quantum mechanics.
A star is actually a fairly complicated system, and has both continuum and discrete features in its spectrum. This is made even more difficult by the fact that a lot of light escapes from regions with very different temperatures. Anyway, the continuous portion of the spectrum is essentially what determines color for our eyes, and it is mostly independent of the star's composition.