An astronomer records the spectrum of light coming from a distant star. Describe what information the astronomer can deduce from this stellar spectrum, and what physical principles she would apply
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The spectrum of light from a star will be an absorption spectrum.
The astronomer can examine the continuous radiation in the spectrum to determine the wavelength of peak intensity. Using Wien's law, this will enable the astronomer to determine the surface temperature of the star.
The absorption spectrum will contain isolated regions where the intensity of the spectrum is very low. These will appear as dark lines on a photographic spectrum. These lines are caused by the absorption of photons from electrons becoming excited to higher energy levels. By comparing the pattern of wavelengths of the dark lines with known values, the astronomer will be able to determine the chemical composition of the cool gas in the atmosphere of the star since each element has its own unique pattern of energy levels and absorption/emission lines.
The entire absorption spectrum pattern may be shifted towards the red or blue end of the spectrum. This is caused by motion of the star toward or away from the observer, and is explained by the Doppler effect.
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