Final answer:
The Doppler effect in light leads to blue or red shifts depending on whether a light source is approaching or receding from the observer. This is pivotal in measuring the radial velocities of celestial bodies and understanding the expansion of the universe, as well as determining rotational speeds of stars and planets.
Step-by-step explanation:
The Doppler effect demonstrates a change in the frequency or wavelength of a wave for an observer who is moving relative to the wave source. Specifically, for light waves, if a source is approaching an observer, the light waves are compressed, leading to a shift towards the blue end of the spectrum; conversely, if the source is moving away, the waves are stretched, leading to a redshift. This phenomenon is used extensively in astrophysics to determine the radial velocities of celestial objects and has played a significant role in deducing the expansion of the universe.
Moreover, the Doppler effect can be observed in rotating objects like stars and planets where one side is coming towards us while the other moves away, allowing us to measure their rotation speeds. This effect is not just limited to light and sound waves but can also occur with any type of wave, such as water waves in certain conditions.