In spectroscopy, Doppler shifts are seen as shifts in what features?

In spectroscopy, Doppler shifts appear as shifts in spectral lines.

A spectral line is a narrow feature associated with radiation emitted or absorbed when atoms, ions, or molecules change energy states. If the source is moving along the observer’s line of sight, the Doppler effect changes the observed frequency and wavelength of those lines. Motion away generally shifts them toward longer, redder wavelengths; motion toward the observer shifts them toward shorter, bluer wavelengths.

Astronomers use these displaced lines to estimate the radial velocities of stars, galaxies, gas clouds, and exoplanet-hosting stars. The same principle works in laboratory spectroscopy, where the motion of particles can produce Doppler broadening as well as a net shift. A spread of velocities broadens a line, while the bulk motion of the emitting material moves its center.

Spectral lines are not the same as diffraction spikes, which are image artifacts caused by telescope structure, or star trails, which result from apparent motion during long exposures. Sunspots are regions on the Sun’s surface, although their spectra can contain shifted and broadened lines. The broader neighboring concept is the spectrum itself: Doppler information is read from the positions and shapes of identifiable spectral features.