starlight

Starlight is the electromagnetic radiation emitted by stars. It spans a broad range of wavelengths, with visible light and nearby infrared and ultraviolet constituting the portion commonly observed from Earth. The light originates from nuclear fusion in a star’s core, is transported to the surface, and is radiated outward into space as the star’s emergent spectrum.

The spectrum resembles a blackbody distribution modified by absorption lines produced by elements in the star’s atmosphere. A star’s color and spectrum are primarily determined by its surface temperature: hotter stars emit more blue light and cooler stars more red, while characteristic spectral lines reveal chemical composition.

As starlight propagates through space and the Earth’s atmosphere, it can be attenuated and reddened by interstellar dust and terrestrial air, respectively. In addition, motions along the line of sight shift spectral lines via the Doppler effect, providing a measure of radial velocity. Observed starlight from a single star is often blended with light from many stars along the line of sight, especially in crowded regions.

Astronomers analyze starlight using photometry and spectroscopy to infer properties such as distance, temperature, chemical composition, and motion. Parallax measurements determine nearby distances; standard candles, like Cepheid variables and Type Ia supernovae, extend distance estimates farther into the cosmos. The aggregate light from all stars contributes to the diffuse background that informs models of the galaxy’s evolution and the universe’s star-formation history.