Question

doppler effect and red / blue shift
explain the doppler effect:
the diagram to the left shows the laboratory spectrum (stationary star) on the bottom and the moving star on the top. is the star moving towards or away from the earth? how do you know?
what happens to wavelength as a galaxy moves towards an observer? longer wavelength.

Explanation:

The Doppler Effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave - source. In the case of light, a blue - shift indicates the source is moving towards the observer (shorter wavelength) and a red - shift indicates it is moving away (longer wavelength). Looking at the spectra, if the spectrum of the moving star is shifted towards the red end compared to the stationary star's spectrum, the star is moving away. When a galaxy moves towards an observer, the wavelength shortens (blue - shift), not lengthens as wrongly stated in the question.

Answer:

1. The Doppler Effect is the change in wave frequency or wavelength due to relative motion between source and observer.
2. The star is moving away from the Earth because if its spectrum is red - shifted compared to the stationary star's spectrum.
3. The wavelength shortens (blue - shift) as a galaxy moves towards an observer.