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What is spectroscopy?

How about:- Analysis of the light (more exactly electromagnetic radiation) coming from a source (star in the narrow context) by splitting it into individual wavelengths/frequencies and quantifying the amount of emission at each wavelength, leading to inferences about composition, temperature, pressure etc.

Chris

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How about:- Analysis of the light (more exactly electromagnetic radiation) coming from a source (star in the narrow context) by splitting it into individual wavelengths/frequencies and quantifying the amount of emission at each wavelength, leading to inferences about composition, temperature, pressure etc.

Chris

Did you ever split light from a slit through a prism at school, so that it split the light into its various colours? Well, spectroscopy is something along those lines but in a far more sophisticated way obviously. :smiley:

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Is it an advanced way of saying "that star is blue - it must be burning sulphur, that star is red - it must be burning helium"?

I was watching a Brian Cox documentary that said astro physicists split a star's light into the spectrum and looked at the gaps in the colours - our sun has a lot of gaps in the yellow part of the spectrum so we know it's burning hydrogen. Is that it?

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Is it an advanced way of saying "that star is blue - it must be burning sulphur, that star is red - it must be burning helium"?

I was watching a Brian Cox documentary that said astro physicists split a star's light into the spectrum and looked at the gaps in the colours - our sun has a lot of gaps in the yellow part of the spectrum so we know it's burning hydrogen. Is that it?

The "gaps" are absorbtion lines created by continuum light passing through a cooler, outer region containg hydrogen and other elements.

Chris

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All stars, including the sun, are "black-bodies" which means that the continuous spectrum of light they emit follows a characteristic peak-shaped curve (the Planck spectrum). The spectral position of the peak gives the temperature of the black-body radiating the light (the term black-body really means that all photons incident on the surface will be completely absorbed and, as there are no reflected photons, all the light we see from it is due to emission). The hotter the body the further into the short-wavelength, high energy, region the of the spectrum the peak appears to be and, hence, very massive hot stars appear blue while less massive cooler stars appear red. As Chris pointed out the light emitted from a star must pass through the cooler outer region of the star and the elements in these outer layers will remove (absorb) photons at very specific energies. These energies are defined by the electronic structure of the elements and each element has its own unique set of energies. When the light from a star is passed through a spectrometer (usually a diffraction grating) a smooth "rainbow" of light is produced with the brightest part (where the black body peak will be) giving the temperature (mass) of the star. This spectrum will have very thin dark lines (absorption lines) crossing it where the lines will correspond to the energies of the photons that have been removed by the elements in the outer layer of the star. These lines therefore allow you to fingerprint the star and know what its chemical composition is. The spectrum also allows you to tell how quickly the star is either moving away or moving towards you as they will be doplar shifted compared to a reference emission source in the lab or our own sun. If the lines are shifted towards the red end of the spectrum then the star is moving away from us (red shifted) and if the lines are moved towards the blue end of the spectrum then the star is moving towards us (blue shifted). This technique can also be used to show the rotation of edge-on galaxies as one side will be blue shifted and the other side will be red shifted.

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  • 2 weeks later...

Is it an advanced way of saying "that star is blue - it must be burning sulphur, that star is red - it must be burning helium"?

I was watching a Brian Cox documentary that said astro physicists split a star's light into the spectrum and looked at the gaps in the colours - our sun has a lot of gaps in the yellow part of the spectrum so we know it's burning hydrogen. Is that it?

Well you're getting there but for now just enjoy the view of staring close and personnel into a DVD with sunlight grazing its surface thus..

post-21003-0-65395100-1342471705_thumb.j

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Basically, its the study of a star's element make-up by observing it's radiated light. Some elements produce "emission" lines while other produce "absorption" lines in the star's light spectra. From a star's spectra, we can tell if it's a very hot, young star or a very old, cool star. From the hottest to coolest, the classification of stars are labled:

O,B,A,F,G,K,M,N. Our Sun is a G2 star and O and B stars are very blue while M and N stars are very red.

In other words, we can determine what the chemical make-up of any star by studying it's light spectra.

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