In the Letters section of the August issue of Physics Today, a reader claims that when he asks 'newly minted physics PhDs' to explain why stars have different colors, that 75% of them answer incorrectly. How would you answer the question?
Eh, it depends on the question asked and how much the person asking already knows.Sorry if I posted too much on this topic. I posted before reading the other responses and noticed everyone is trying to keep it simple. I will do this when possible from now on and not get too technical unless asked to. lol :)
There is no uncertainty of the spectrum of our own star. The uncertainty is in the perceived color, which will be different depending on who you ask and how you are looking at it.There seems to be much uncertainty about the color of our own star, so how is it possible to be certain about the color of stars many light years away? I see white, yellow, blu-ish and even pink are suggested.
Wouldn't an ND filter used on a regular camera, from the space station say, show the true color?
You make it sound easy, but from a quick look into how star colors are measured, it doesn't look so easy. I looked at this site to start with:When we talk about "star colors" we actually mean the spectrum that it emits. We are very easily able to measure this spectrum to a very very high accuracy.
No, to measure the spectrum of a star we use a spectrograph. This spreads the light out like a prism instead of focusing it onto one spot. Spectrographs must be calibrated of course, but that is not terribly difficult as far as I know.I'm no scientist so excuse my perhaps naive questions. SOLSPEC does have error margins, and needs regular calibration. It is also looking at the nearest star, so is quite large. The next nearest star though, and all the others, are only going to resolve to 1 pixel even from our most powerful instruments, aren't they?
A spectrograph shows you which wavelengths are being emitted and absorbed.Secondly, if we are examining spectra, through filters, how is it determined that the spectra are thermal in origin rather than from ionisation of elements in a stars electric field? If we look through a red filter, how do we know that we are not seeing a Balmer line of hydrogen?
Of course. The spectrum of a star is not a perfect black body, it will have all kinds of things that make it slightly different. These are all seen the in spectrum as different emission/absorption lines, broadening of the lines, etc.And lastly, what about Stark or Zeeman shifting, does those come into play in these measurements?
(Dons flak jacket and stands well back...)