Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.
There are 2759 entries in this glossary.| Term | Definition |
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| Ut |
Abbreviation for Universal Time.
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| Utc |
Abbreviation for Coordinated Universal Time.
See also: Universal Time.
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| Utopia Planitia |
An extensive, sparsely cratered plain in the northern hemisphere of Mars. It was the landing site for the Viking 2 spacecraft. Panoramic images returned by the Viking lander showed terrain littered with large numbers of boulders made of open-textured rock.
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| Uv |
Abbreviation for ultraviolet.
See also: electromagnetic radiation, ultraviolet astronomy.
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| Uv Ceti Star |
A flare star.
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| Uvby Photometry |
A photometric system introduced by B. Strömgren in the late 1950s. It is based on the measurement of magnitudes through each of four intermediate-band filters centred on the wavelengths 350 u, 410 v, 470 b and 550 y nanometres. The y band corresponds closely with the V band of UBV photometry and traditional visual magnitudes. The v band covers the Balmer line Hd and many other lines in the spectra of cooler stars. The b band, half-width 18 nanometres, lies close to but excludes the Balmer line Hb. The u band is in the ultraviolet, between the atmospheric cut-off at 320 nanometres and the Balmer decrement. The use of the system is intended to provide information about the spectra and physical properties of individual stars and groups of stars without the much longer process of studying spectra in detail.
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