How did the spectrum help determine if a galaxy was moving closer or further away? short and small

The spectrum of a galaxy reveals its light, which can show shifts in wavelengths due to the Doppler effect. If the spectral lines are shifted towards the red end (redshift), the galaxy is moving away. If the lines are shifted towards the blue end (blueshift), it is moving closer. This analysis of spectral shifts allows astronomers to determine the galaxy's movement relative to Earth.