Astronomical spectroscopy

Astronomical spectroscopy analyzes the wavelengths and intensities of light from celestial objects to infer their composition, temperature, motion, and other physical properties.

Electromagnetic spectrum: The full range of electromagnetic radiation, ordered by frequency or wavelength. Spectroscopy measures celestial radiation across selected parts of this full wavelength range.
Atomic spectral line: A narrow spectral feature produced when an atom absorbs or emits photons at specific energies. Its characteristic wavelength can identify an element in a celestial spectrum.
Stellar classification: The organization of stars into types based chiefly on their spectra and temperatures. Stellar spectra supply the line patterns used to assign spectral classes.
Fraunhofer lines: Dark absorption lines in the Sun's spectrum catalogued by Joseph von Fraunhofer in the early nineteenth century. Their systematic study established that solar light contains a rich pattern of spectral features.
Emission spectrum: A pattern of wavelengths emitted by atoms, ions, molecules, or other sources. Bright emission lines reveal excited gases in nebulae and stellar atmospheres.
Quantum mechanics: The physical theory describing matter and radiation at atomic and subatomic scales. Quantized energy levels explain why atoms produce discrete spectral lines.
Radial velocity method: A method for detecting orbiting objects by measuring periodic Doppler shifts in a star's spectrum. Precise spectral shifts reveal the gravitational pull of orbiting exoplanets.
Joseph von Fraunhofer: A German physicist and optical instrument maker who mapped dark lines in the solar spectrum. His precise observations made solar spectral lines landmarks for later astronomical measurements.
Absorption spectrum: A pattern of reduced intensities at wavelengths absorbed by matter along a light path. Dark lines in starlight identify elements in cooler gas between the source and observer.
Spectrograph: An instrument that separates incoming light by wavelength and records its intensity. It converts celestial light into the measurable spectrum used for analysis.

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