OK this is propably a stupid question but when you have your telescope pointed at the desired star you want, and you are analysing the light with your spectrograph, how do you know that all the light you are analysing is coming from that star. Will you not get stray light from other stars and from light pollution etc.
That's not a stupid question. What ya do first is you take the spectrum of the dark current. And you also take a solar spectrum of the day time sky and maybe the night sky in the vicinty of the lights but not directly at the lights. You then subtract off these spectra from your target.
Thanks for the info Karl. But would you still not have a problem with light from other stars that may be close to the one you are trying to get a specturm from.
  