Chapter 6: Q63P (page 1251)
One of the wavelengths of light emitted by hydrogen atoms under normal laboratory conditions is in the red portion of the electromagnetic spectrum. In the light emitted from a distant galaxy this same spectral line is observed to be Doppler-shifted to in the infrared portion of the spectrum. How fast are the emitting atoms moving relative to the earth? Are they approaching the earth or receding from it?
Short Answer
The speed of emitting atoms moving relative to the earth is .