Final answer:
The Doppler effect occurs with all wave types when there is relative motion between the source and observer, changing the observed frequency. It's essential in astronomy for measuring radial velocities to detect planets and understand galaxy recession, with no effect from sideways motion. The Doppler effect has deeply influenced modern physics and our knowledge of the universe.
Step-by-step explanation:
The Doppler effect is a phenomenon observed when there is relative motion between a wave source and an observer. It occurs with all types of waves, including sound, light, and water waves. When the source of the waves is moving toward or away from an observer, the observed frequency of these waves changes.
In astronomy, the Doppler effect enables scientists to measure a star's radial velocity, which is its speed toward or away from the observer. This measurement is vital for various purposes, like detecting exoplanets through the induced wobble of their host stars or understanding the recession of galaxies. However, no Doppler effect is observed when the motion is perpendicular to the line of sight, because this sideways motion does not affect the frequency as received by the observer.
To calculate the radial velocity using the Doppler effect, one needs the speed of light, the original emitted wavelength, and the observed wavelength; the speed of light being a constant allows accurate velocity determination. This principle has had profound implications on our understanding of the universe's origins and modern physics.