Question

If the rest wavelength of a certain line is 600 nm, but we observe it at 594 nm, then
A) the source is approaching us at 1 % of the speed of light.
B) the source is approaching us at 0.1 % of the speed of light.
C) the source is receding from us at 10% of the speed of light.
D) the source is getting 1% hotter as we watch.
E) the source is spinning very rapidly, at 1% of the speed of light.

Answer

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