When the star moves away from us, its spectrum looks slightly redder. When a star moves toward us, its wavelengths get compressed, and its spectrum becomes slightly bluer.

These wavelength shifts can be seen in the form of subtle changes in its spectrum, the rainbow of colors emitted in light. In astronomy, that source can be a star that emits electromagnetic waves from our vantage point, Doppler shifts occur as the star orbits around its own center of mass and moves toward or away from Earth. In contrast, waves emitted by a source traveling away from an observer get stretched out.

Waves emitted by an object traveling toward an observer get compressed - prompting a higher frequency - as the source approaches the observer. The Doppler effect, or Doppler shift, describes the changes in frequency of any kind of sound or light wave produced by a moving source with respect to an observer. To date, 442 of the 473 known exoplanets have been detected using the Doppler effect, which also helps planetary scientists glean details about the newly found planets. The effect is useful in a variety of different scientific disciplines, including planetary science: Astronomers rely on the Doppler effect to detect planets outside of our solar system, or exoplanets. Many students learn about the Doppler effect in physics class, typically as part of a discussion of why the pitch of a siren is higher as an ambulance approaches and then lower as the ambulance passes by.

Doppler effect example