How do astronomers use a spectrum to find out what gases are in a star?
Because specific elements and gases produce spectral features called 'emission
and absorption lines' at specific wavelengths. Like fingerprints, these lines
can be compared to similar lines found in these gases under laboratory
conditions, and this lets astronomers determine the composition of distant
stars and gas clouds. Depending on the circumstances, these lines are found in
all parts of the electromagnetic spectrum from x rays to radio frequencies.
You can visit the National Institute of Standards and Technology and use their web interface to explore the atomic lines found in any spectral region in the visible spectrum. For example, enter a base wavelength of 6500 and a search range of +/- 10 Angstroms and you will see over 50 lines from many familiar atoms!
Copyright 1997 Dr. Sten Odenwald
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