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Lines of 6877 Å, 4989 Å and 4548 Å are observed in the visible range of the spectrum of a certain galaxy. To what substance do they belong? What can you say about the motion of this galaxy?

Answer»


Solution :The spectral lines in question closely resemble the first three lines of the BALMER series of the hydrogen spectrum: 6563 Å, 4861 Å and 4340 Å. To make SURE that they are in fact the lines, find the ratio of the wavelengths of the galaxy spectrum to the wavelengths RADIATED in the laboratory. We SHALL obtain identical ratios:
`lamda/lamda_(0)=6877/6563=4980/4861=4548/4340=1.045`
The red shift is DUE, obviously, to the motion of the galaxy away from us (the Doppler effect). We have
`lamda=lamda_(0)sqrt((1+beta)/(1-beta)),"where "sqrt((1+beta)/(1-beta))=1.045`
Solving this equation we find the speed at which the galaxy moves away from us.


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