How do scientists use the doppler effect to measure the actual motion of stars?

If the light waves are coming more frequently, then we know the star is moving toward earth. if the light waves are coming more slowly, we know the star is moving away. this is because the star gives the illusion that the light waves are coming at a slower pace when in fact, the frequency is the same the whole time

The did multiple things that the economy

Any time if 18 but would need the money