Answer :
Choice D). is on the right track, but it's stated incorrectly.
The wavelengths of light coming from a galaxy that's moving toward us are
shorter than they were when they left the galaxy. When we see them, they're
shorter than they should be.
(This is called a "blue shift" in the spectrum of the galaxy, because blue is the
short-wavelength end of the spectrum of visible light. If the wavelength of some
light somehow becomes shorter, then the color of the light changes toward the
direction of blue.)
If the source of light is moving toward us, then the wavelength we see is shorter
than it should be. If the source is moving away from us, then the wavelength
we see is longer than it should be. The whole trick to this is knowing what the
wavelength of the light we see should be !
The wavelengths of light coming from a galaxy that's moving toward us are
shorter than they were when they left the galaxy. When we see them, they're
shorter than they should be.
(This is called a "blue shift" in the spectrum of the galaxy, because blue is the
short-wavelength end of the spectrum of visible light. If the wavelength of some
light somehow becomes shorter, then the color of the light changes toward the
direction of blue.)
If the source of light is moving toward us, then the wavelength we see is shorter
than it should be. If the source is moving away from us, then the wavelength
we see is longer than it should be. The whole trick to this is knowing what the
wavelength of the light we see should be !
