U
- UBV photometric systemWide-band photometric system used in astronomy
- UESACAstronomical survey
- Uhuru (satellite)Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It
- UHZ1UHZ1 is a background galaxy containing a quasar. At a redshift of approximately 10.1, UHZ1
- Ukrainian T-shaped Radio telescope, second modificationThe Ukrainian T-shaped Radio telescope, second modification (official abbreviation UTR-2)
- Ultimate fate of the universeTheories about the end of the universe
- Ultra-cool dwarfAn ultra-cool dwarf is a stellar or sub-stellar object that has an effective temperature l
- Ultra-high-energy cosmic rayCosmic-ray particle with a kinetic energy above 1 EeV
- Ultraluminous X-ray sourceType of x-ray source
- Ultraviolet astronomyObservation of electromagnetic radiation at ultraviolet wavelengths
- Ulysses (spacecraft)NASA/ESA solar probe launched in 1990
- Ulysses PaxtonUlysses Paxton is a fictional character created by Edgar Rice Burroughs in his novel The M
- Umbilical cableAn umbilical cable or umbilical is a cable and/or hose that supplies required consumables
- Umbra, penumbra and antumbraDistinct parts of a shadow
- UmbrielMoon of Uranus
- Unbarred spiral galaxyType of spiral galaxy without a central bar
- Uncertainty parameterParameter introduced by the Minor Planet Center
- United Nations Committee on the Peaceful Uses of Outer SpaceThe United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) is a United Nati
- United States Naval ObservatoryScientific agency in the United States
- United States Naval Observatory Flagstaff StationThe United States Naval Observatory Flagstaff Station (NOFS), is an astronomical observato
- Universal TimeTime standard based on the slowing rotation of the Earth
- UniverseEverything in space and time
- Uppsala General CatalogueCatalogue of galaxies visible from the northern hemisphere
- Uppsala–DLR Asteroid SurveyAstronomical survey
- Uppsala–DLR Trojan SurveyAsteroid survey
- UranusSeventh planet from the Sun
- Uranus Orbiter and ProbeProposed NASA space mission to Uranus
- Ursa MajorConstellation in the northern sky
- Ursa MinorConstellation in the northern celestial hemisphere
- UY ScutiStar in the constellation Scutum