Stellar spectroscopy

Stellar spectroscopy studies the wavelengths and patterns of starlight to infer stars’ chemical compositions, temperatures, motions, and physical conditions.

Electromagnetic spectrum: The full range of electromagnetic radiation, arranged by wavelength or frequency. Stellar spectra sample portions of this range, including visible, ultraviolet, and infrared light.
Black-body radiation: Electromagnetic radiation emitted by an ideal absorber whose spectrum depends only on temperature. It approximates the smooth continuum beneath many stellar absorption lines.
Stellar abundance: The relative amounts of chemical elements present in a star. Line strengths and atmospheric models are used to estimate stellar element abundances.
Photometry: The measurement of an object's brightness through selected wavelength bands. Unlike spectroscopy, photometry usually records broad-band brightness rather than detailed wavelength features.
Atomic spectral line: A narrow wavelength feature produced when atoms emit or absorb photons during transitions between energy levels. Stellar absorption and emission lines identify atoms in a star’s atmosphere.
Kirchhoff's laws of spectroscopy: Rules describing how hot dense matter, hot low-density gas, and cooler gas in front of a source produce distinct spectra. They explain why stars show absorption lines while surrounding hot gas can produce emission lines.
Radial velocity: An object's velocity component along the line of sight, inferred from its Doppler shift. Stellar line shifts measure approach or recession relative to an observer.
Interferometry: A technique that combines waves from multiple telescopes to obtain high angular resolution. It resolves stellar sizes and surface structure rather than primarily identifying spectral features.
Doppler spectroscopy: A method that infers motion from wavelength shifts caused by the Doppler effect. Shifts in stellar lines reveal motion along the line of sight.
Stellar atmosphere: The outer layers of a star from which most observed light escapes. Most diagnostic stellar spectral features form in these layers.

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