U
- UARS – (spacecraft) Upper Atmosphere Research Satellite, a satellite used to study the Earth's upper atmosphere
- UCAC – (catalog) USNO CCD Astrometric Catalog
- UESAC – (observing program) Uppsala-ESO Survey of Asteroids and Comets
- UFO – (astrophysics terminology) Unidentified Flying Object
- UG – (celestial object) U Geminorum, a class of cataclysmic variable stars (also known as dwarf novae) that are named after U Geminorum, the archetype for the class
- UGSS – (celestial object) UG SS Cygni, a subclass of UG-type stars named after SS Cygni, the archetype for the subclass
- UGSU – (celestial object) UG SU Ursae Majoris, a subclass of UG-type stars named after SU Ursae Majoris, the archetype for the subclass
- UGWZ – (celestial object) UG WZ Sagittae, a subclass of UG-type stars named after WZ Sagittae, the archetype for the subclass
- UGZ – (celestial object) UG Z Camelopardalis, a subclass of UG-type stars named after Z Camelopardalis, the archetype for the subclass
- UGC – (catalog) Uppsala General Catalogue, a catalog of galaxies
- UIT – (telescope) Ultraviolet Imaging Telescope, an ultraviolet telescope that was operated from the cargo bay of the Space Shuttle
- UKIDSS – (observing program/catalog) UKIRT Infrared Deep Sky Survey
- UKIRT – (telescope) United Kingdom Infrared Telescope
- UKSA – (organization) UK Space Agency
- UKST – (telescope) United Kingdom Schmidt Telescope
- ULIRG – (celestial object) UltraLuminous InfraRed Galaxy, a galaxy that is brighter than 1012 solar luminosities in the infrared
- ULX – (celestial object) UltraLuminous X-ray source
- UMS – (celestial object) Upper Main Sequence, the more massive hydrogen-burning main-sequence stars
- USAF – (organization) United States Air Force
- USGS – (organization) United States Geological Survey
- USNO – (organization) United States Naval Observatory
- UT – (astrophysics terminology) Universal Time
- UTC – (astrophysics terminology) Coordinated Universal Time
- UV – (astrophysics terminology) UltraViolet
- UVS – (instrumentation) UltraViolet Spectrometer, the name of instruments on the Voyager and Galileo spacecraft
- UXOR – (celestial object) UX ORionis objects, a class of variable pre–main sequence stars named after UX Orionis, the archetype for the class
Read more about this topic: List Of Astronomy Acronyms