U Geminorum star
UARS (Upper Atmosphere Research Satellite)
UBV system
Uchinoura Space Center
UDMH (unsymmetrical dimethylhydrazine)
UFO (UHF Follow-On) satellites
UFOs
Uhuru
Ulam, Stanislaw Marcin (1909-1984)
Ulam spiral
Ulinski, Franz Abdon (1890-1974)
ullage
ulna
Ultra Long-Duration Balloon (ULDB) Project
ultra-cool star
ultra-luminous cluster
ultra-luminous infrared galaxy (ULIRG)
ultraviolet (UV)
ultraviolet lasers, interstellar signaling via
Ulysses
umbilical connections
umbilical cord
umbilical swing arm
umbilical tower
umbra
Umbriel
Ume
uncertainty principle
uncountable set
underdeck spray
undershoot boundary
undulating number
unduloid
UnEX (University-class Explorer)
unexpected hanging
unicellular
unidentified flying objects (UFOs)
uniformity, principle of
uniform polyhedron
unilluminable room problem
union
unique number
unit circle
unit cube
unit fraction
United Kingdom Infrared Telescope (UKIRT)
United Kingdom Schmidt Telescope (UKST)
United Space Alliance
UNITS
universal approximation
universal computation
universal computer
Universal Library
Universal Time (UT)
universal translator
universe
universe of discourse
University of California, Berkeley
unpaired spin
unrestricted burn
unseen companion
untouchable number
Uosat
uplink
upper transit
upside-down picture
Upsilon Andromedae
uracil
uracil
uranium
Uranus
Uranus, moons
Uranus, rings
Urca process
urea
ureilite
ureter
urethra
Urey, Harold Clayton (1893-1981)
uric acid
urinary bladder
urinary system
urine
Ursa Major (constellation)
Ursa Major Groups
Ursa Major Moving Cluster
Ursa Minor (constellation)
Ursa Minor Dwarf
47 Ursae Majoris
US Air Force study on teleportation
US Naval Observatory
Usher syndrome
USRA (Universities Space Research Association)
Ussher, James (1581-1656)
uterine cancer
uterine cancer treatment
uterus
uterus, disorders of
utility function
Utopia Planitia
utriculus
UU Herculis star
UV Ceti star
UV Raman and fluorescence spectroscopy
uvea
UX Orionis
UX Ursae Majoris star