State what is meant by a Doppler shift and describe how it was used to study the movement of galaxies.

Doppler shift can be described as the fractional change in wavelength due to relative motion between an observer and a wave source. The wavelength of a line in the spectrum of light emitted by a distant region of space can be compared to the same line found by the same wave reproduced in a laboratory.Where a increase in wavelength is found between the observer and the distance galaxy, it can be deduced that the galaxy is moving away from the observer and visa versa if the there is a decrease in the relative wavelength. We can use a formula (Change in wavelength/original wavelength = velocity of distant galaxy/speed of light) to determine the relative velocity of a receding galaxy.