Ultraviolet astronomy

Lore & Background

Ultraviolet line spectrum measurements (spectroscopy) are used to discern the chemical composition, densities, and temperatures of the interstellar medium, and the temperature and composition of hot young stars. UV observations can also provide essential information about the evolution of galaxies and can discern the presence of a hot white dwarf or main sequence companion in orbit around a cooler star. Most stars are relatively cool objects emitting much of their radiation in visible or near-infrared, so in ultraviolet light most stars would fade, while very young massive stars and very old stars and galaxies near their birth or death would be visible. Clouds of gas and dust would block vision in many directions along the Milky Way.

Space-based solar observatories such as SDO and SOHO use ultraviolet telescopes (called AIA and EIT, respectively) to view activity on the Sun and its corona. Weather satellites such as the GOES-R series also carry telescopes for observing the Sun in ultraviolet. The Hubble Space Telescope and FUSE have been the most recent major space telescopes to view the near and far UV spectrum of the sky, though other UV instruments have flown on smaller observatories such as GALEX, as well as sounding rockets and the Space Shuttle. Pioneers in ultraviolet astronomy include George Robert Carruthers, Robert Wilson, and Charles Stuart Bowyer.

Reader's Guide

Ultraviolet astronomy is notable because it reveals phenomena invisible to the human eye and largely blocked by Earth's atmosphere, requiring space-based or high-altitude observation. The article lists numerous ultraviolet space telescopes, from the Far Ultraviolet Camera/Spectrograph on Apollo 16 (April 1972) to the International Ultraviolet Explorer (1978–1996) and the Hubble Space Telescope (various instruments from 1990 onward). These missions have enabled spectroscopy to determine chemical composition, densities, and temperatures of the interstellar medium, as well as the temperature and composition of hot young stars. UV observations also provide essential information about galaxy evolution and can detect hot companions orbiting cooler stars. The article notes that most stars are cool and emit little UV, so the ultraviolet sky is dominated by hot objects in early or late evolutionary stages. Solar observatories like SDO and SOHO, and weather satellites like GOES-R, use UV telescopes to monitor solar activity. Planetary spacecraft such as Cassini, MESSENGER, New Horizons, Juno, and MAVEN have carried UV instruments to study other worlds. The legacy of ultraviolet astronomy is a deeper understanding of the hot, energetic universe and the life cycles of stars and galaxies.