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.

Question

Quizplus · Accepted Answer

The observed wavelength is shorter than the rest wavelength, indicating a blueshift, which means the source is approaching us. The change in wavelength (600 nm - 594 nm = 6 nm) divided by the rest wavelength (600 nm) gives a 1% change, which corresponds to the source moving towards us at 1% the speed of light.

If the Rest Wavelength of a Certain Line Is 600