If the rest of 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: A