fuv

FUV stands for far ultraviolet, a region of the electromagnetic spectrum with wavelengths roughly 122 to 200 nanometers. It lies beyond the reach of standard optical photometry on Earth because the atmosphere strongly absorbs ultraviolet radiation, making space-based observations essential. The term is frequently used in astronomy to describe both the spectral region and the data products derived from it.

In astronomy, FUV photons originate primarily from very hot, young, massive stars and from accretion processes around compact objects. The FUV range hosts important spectral lines from ionized species and allows studies of the interstellar and intergalactic medium, including the Lyman series of hydrogen and metal lines such as C IV, Si IV, and O VI at nearby wavelengths. FUV observations constrain star formation histories, galaxy evolution, and the physics of hot gas.

Key missions and instruments include the Galaxy Evolution Explorer (GALEX), which mapped the sky in FUV and near-ultraviolet; the International Ultraviolet Explorer (IUE); and the Hubble Space Telescope instruments STIS and COS, which perform high-resolution spectroscopy in the FUV. Future projects continue to rely on space telescopes to access this spectral window.

Photometric systems in the FUV use flux density measurements and AB magnitudes; FUV data are often expressed in photon flux units or erg s−1 cm−2 Å−1. Extinction by dust in galaxies and the Milky Way strongly affects FUV observations, requiring careful correction. Instrument calibration, detector sensitivity, and material transmission across the FUV range are critical for accurate results.