An astronomer observes that light from a distant galaxy is blue-shifted compared to the same wavelength of light observed on Earth.
Which of the following correctly describes the astronomer's conclusion?
Observed wavelength is longer than on Earth; the galaxy is moving away from Earth
Observed wavelength is longer than on Earth; the galaxy is moving towards Earth
Observed wavelength is shorter than on Earth; the galaxy is moving away from Earth
Observed wavelength is shorter than on Earth; the galaxy is moving towards Earth