What do the colors of a distant object reveal about its properties?
by 
Marguerite
ANSWERS: 3
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You are not suffering from long sightedness. LOL :D
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The basic assumption is that the laws of physics and chemistry are the same everywhere in the observable universe. Light from distant luminous objects is passed through a spectrometer (similar to a glass prism) that precisely measures wavelengths, which by quantum theory is related to the energies of electron transitions. The individual wavelengths show up as 'lines' in the spectrum (for example, look at a street light through a prism). Bottom line (forgive the pun): You can infer much of an object's chemistry and temperature by comparing its spectrum to that of known substances in labs on earth. This has yielded deep understanding of astrophysical processes. "Color" is sometimes used as a dumbed-down euphemism for "spectrum".
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Primarily it tells us the velocity of the object away from or towards us. An object moving away has its light shifted towards the red end of the spectrum and such universals as frauenhofer lines are equally shifted in direct proportion to the velocity away from us. http://en.wikipedia.org/wiki/Fraunhofer_line Secondarily we use this to estimate the distance to the object on the assumption that the objects moving away fastest tend to be furthest away in out expanding universe. regards JakobA
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