Term Index (U)
- U: photometric filter for ultraviolet light
- U band:
- U: photometric filter for ultraviolet light
- U filter:
- U: photometric filter for ultraviolet light
- U Geminorum variable:
- U-B:
- color index: a number that characterizes the color of an object
- UAI:
- UARS:
- UBV:
- UBV photometric system: commonly-cited photometric system for describing stars' colors
- UBVI photometric system:
- UBVRI photometric system:
- ubvy98:
- UC Santa Cruz:
- UCAC:
- UCAC-3:
- UCD:
- UCHII:
- HII region (HII): cloud of partially-ionized atomic hydrogen
- UCLES:
- UCSD Cosmic X-ray Experiment:
- OSO 7: 1970s observatory-satellite for viewing the Sun
- UCSD Hard Solar X-ray Monitoring Instrument:
- OSO 7: 1970s observatory-satellite for viewing the Sun
- UDF:
- UDFj:
- UDFy:
- UDG:
- UDS:
- UDXS:
- UKIDSS: five-part infrared survey using UKIRT
- UESAC:
- UFD:
- UFT:
- UFTI:
- UG:
- UG SS Cygni variable:
- dwarf nova (DN): flash of a cataclysmic variable star
- UG SU Ursae Majoris:
- dwarf nova (DN): flash of a cataclysmic variable star
- UG WZ Sagittae:
- dwarf nova (DN): flash of a cataclysmic variable star
- UG Z Camelopardalis:
- dwarf nova (DN): flash of a cataclysmic variable star
- UGC:
- UGC 7654:
- M87: supergiant elliptical galaxy in local universe
- UGCA:
- UGCS:
- UKIDSS: five-part infrared survey using UKIRT
- UGP:
- UGPS:
- UKIDSS: five-part infrared survey using UKIRT
- UGSS:
- dwarf nova (DN): flash of a cataclysmic variable star
- UGSU:
- dwarf nova (DN): flash of a cataclysmic variable star
- UGWZ:
- dwarf nova (DN): flash of a cataclysmic variable star
- UGZ:
- dwarf nova (DN): flash of a cataclysmic variable star
- UH Hilo Hoku Ke'a:
- UH88:
- UHE:
- UHE cosmic rays:
- cosmic rays (CR): very-high-energy particles from beyond the solar system
- UHE gamma ray:
- UHECR:
- cosmic rays (CR): very-high-energy particles from beyond the solar system
- UHEGR:
- Uhuru: 1970 satellite X-ray telescope
- UIST:
- UIT:
- UK:
- UK Schmidt Southern Sky Survey:
- UK Schmidt Survey: photographic survey of the southern hemisphere sky
- UK Schmidt Telescope (UKST): 1.2 meter telescope in Australia with wide field-of-view
- UKIDSS: five-part infrared survey using UKIRT
- UKIRT:
- UKIRT Infrared Deep Sky Survey:
- UKIDSS: five-part infrared survey using UKIRT
- UKST:
- ULAS:
- UKIDSS: five-part infrared survey using UKIRT
- ULEIS:
- ULF:
- ULIRG:
- Ultima Thule:
- Ultimate Spitzer Phase Curve Survey (USPCS): investigation of exoplanet atmospheres
- ultra diffuse galaxy (UDG): a galaxy with extremely low luminosity
- ultra low frequency (ULF): electromagnetic radiation, frequency 300 Hz to 3 kHz
- ultra-compact dwarf galaxy:
- ultra-cool dwarf:
- ultra-faint dwarf galaxy (UFD): recently discovered faint dwarf galaxies in the Local Group
- ultra-high energy cosmic rays:
- cosmic rays (CR): very-high-energy particles from beyond the solar system
- ultra-high-energy:
- ultra-high-energy gamma ray:
- ultra-high-energy gamma rays (UHEGR): energetic gamma rays with more than 100 TeV photon energy
- ultra-light axion:
- axion (A0): proposed light, electrically neutral elementary particle
- ULTRACAM:
- ultracompact HII region:
- HII region (HII): cloud of partially-ionized atomic hydrogen
- ultracool dwarf: star or brown dwarf cooler than M7 class
- SPECULOOS: search for Earth-like exoplanets orbiting nearby dim stars
- ultralight repulsive dark matter:
- ultraluminous infrared galaxy (ULIRG,ELF): a galaxy emitting a more far infrared than an LIRG
- Ultraluminous X-ray source:
- ultrarelativistic:
- ultrarelativistic speed:
- ULTRASAT: plan for a satellite to detect UV transients
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- ultraviolet astronomy: astronomy observation and analysis of UV
- ultraviolet catastrophe:
- Ultraviolet Coverage of the Panchromatic Hubble Ultra Deep Field:
- Ultraviolet Hubble Ultra-deep Field (UVUDF): ultraviolet data covering the Hubble Ultra Deep Field region of the sky
- Ultraviolet Imaging Telescope (UIT): 1990s ultraviolet space telescope used on two Space Shuttle missions
- ultraviolet light:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- ultraviolet source:
- Ultraviolet Transient Astronomy Satellite:
- ULTRASAT: plan for a satellite to detect UV transients
- UltraVISTA: near infrared survey using VISTA telescope
- VISTA: 4.1 meter telescope in Paranal Observatory in Chile
- ULX:
- Ulysses: space mission to observe the Sun from off the ecliptic
- UMa:
- UMa II dSph:
- Umbriel:
- moon: a planet's natural satellite, such as Earth's
- Uranus: second outer-most solar system planet
- unbarred:
- bar: central feature of some spiral galaxies
- unbarred galaxy:
- unbarred lenticular galaxy:
- bar: central feature of some spiral galaxies
- unbarred spiral galaxy:
- bar: central feature of some spiral galaxies
- unbound GMC:
- uncertainty principle:
- UNH Solar Gamma-ray Monitor:
- OSO 7: 1970s observatory-satellite for viewing the Sun
- unified atomic mass unit:
- dalton (Da,u): mass unit used on atomic scale
- unified field theory:
- uniform theory of diffraction:
- unit:
- angstrom (Å): unit of length 10-10 meters
- arcsecond (arcsec,sec,second of arc): a 3600th of an angular degree
- astronomical unit (AU): about 93 million miles
- atm: unit of pressure
- dalton (Da,u): mass unit used on atomic scale
- dex: a number or factor's log base 10
- electron volt (eV): very small unit of energy
- erg: CGS unit of energy
- foe: unit of energy on the order of a supernova's output
- Gal: gravimetry unit of the effect of a planet's gravity
- gauss (G,Gs): measurement of magnetic field β
- gigayear (Gy,Gyr): a billion years
- jansky (Jy): unit of measurement of spectral flux density
- joule (J): SI unit of energy
- kelvin (K): temperature scale starting at absolute zero
- light-year (ly): distance that light travels in a year
- mole (mol): unit roughly the count of hydrogen atoms in a gram
- parsec (pc): about 3.26 light-years
- siemens (S): SI unit of electrical conductance
- solar mass (MSun,Msun): mass unit representing the mass of the Sun
- solar neutrino unit (SNU): unit for the detection rate of neutrino detectors
- tesla (T): unit of magnetic flux density
- torr: unit of pressure approximately a millimeter of mercury on Earth
- watt (W): SI unit of power
- United Kingdom Infrared Telescope (UKIRT): Mauna Kea 3.8 meter infrared telescope
- United States Naval Observatory:
- United States Naval Observatory Flagstaff Station:
- universal gas constant:
- universal time:
- time standard: method of designating points in time and quantifying time periods
- universe:
- University of Bonn:
- University of California:
- University of Cambridge:
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- University of Chicago:
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- University of Cologne:
- University of Hawaii:
- IRTF: Mauna Kea 3-meter infrared telescope
- University of Hawaii Institute for Astronomy:
- University of Heidelberg:
- University of Texas Radio Astronomy Observatory:
- University of Tokyo:
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- University of Tokyo Atacama Observatory (TAO): observatory for a 6.5 m infrared telescope under construction
- University of Toronto:
- University of Tubingen:
- Uniview: planetarium software
- unnormalized PDF:
- unnormalized PMF:
- unresolved source:
- extended source: term for astronomical object producing EMR that can be focused
- point source: celestial object that focuses to a point or single Airy disk
- radio source (RS): something in the sky generating radio signal
- unstable isotope:
- isotope: subclass of an element with a specific number of nucleons
- up quark:
- UPG:
- Upper Atmosphere Research Satellite (UARS): 1990s spacecraft to observe Earth ozone layer
- Upper-Scorpius OB Association:
- Uppsala General Catalogue (UGC): 1973 catalog of galaxies visible from northern hemisphere
- Uppsala General Catalogue of Galaxies:
- Uppsala-ESO Survey of Asteroids and Comets (UESAC): 1990s comet and asteroid survey
- Uranometria:
- Uranus: second outer-most solar system planet
- giant planet: planet of more than 10 Earth masses
- ice giant: planet more massive than gas planets and less than rocky planets
- Neptune: outer-most solar system planet
- ring system: disk or set of rings orbiting a planet
- shepherd moon: small moon at outer edge of a ring
- Voyager: space probes to observe planets and the edge of the solar system
- URAP:
- Ulysses: space mission to observe the Sun from off the ecliptic
- URAT:
- URAT-1:
- Urca process: neutrino-emitting process
- Urey:
- Ursa Major Filament:
- Ursa Major I:
- Ursa Major II Dwarf: dwarf spheroidal galaxy in the Local Group
- Ursa Minor:
- US Air Force:
- LINEAR: survey of near-Earth objects
- US Navy:
- USNO: observatory obtaining astronomical data for Naval use
- USA:
- USAC:
- USAC-1:
- USAC-2:
- USAC-3:
- USAC-4:
- USAC-5:
- UScoCTIO:
- USNO: observatory obtaining astronomical data for Naval use
- USNO CCD Astrograph:
- USNO CCD Astrograph Catalog (UCAC): USNO star catalog including proper motions
- USNO Robotic Astrometric Telescope:
- USNO Twin Astrograph: USNO astrograph deployed in 1970
- USNO-A:
- NOMAD: astrometric star catalog
- USNO: observatory obtaining astronomical data for Naval use
- USNO-B:
- NOMAD: astrometric star catalog
- USNO: observatory obtaining astronomical data for Naval use
- USO/RS:
- USPCS:
- USS Sources: catalog of sources with steep spectral index
- UT:
- time standard: method of designating points in time and quantifying time periods
- UT1 Telescope:
- UT2 Telescope:
- UT3 Telescope:
- UT4 Telescope:
- UTC:
- time standard: method of designating points in time and quantifying time periods
- UTMOST: telescope aiming to detect radio transients
- UTRAO:
- UUDS:
- UKIDSS: five-part infrared survey using UKIRT
- UV:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- UV astronomy:
- UV SFR:
- UV source:
- UV star formation rate:
- UV, optical, and infrared:
- UVOIR: a spectral "band name" covering UV, visible light, and IR
- UVA:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- UVB:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- uvby photometric system:
- uvby system:
- UVC:
- ultraviolet (UV): electromagnetic radiation, wavelength 10-400 nm
- UVCS:
- UVES:
- UVIS:
- Cassini: explorer spacecraft sent to Saturn
- UVOIR: a spectral "band name" covering UV, visible light, and IR
- UVOIR astronomy:
- UVOIR: a spectral "band name" covering UV, visible light, and IR
- UVOT:
- Swift: satellite for studying gamma-ray bursts
- UVOTSSC1:
- Swift: satellite for studying gamma-ray bursts
- UVS:
- Europa Clipper: planned Europa space probe
- JUICE: mission to Jupiter in development
- Juno: mission to Jupiter
- Voyager: space probes to observe planets and the edge of the solar system
- UVS/EUV:
- Galileo: circa 1990s space mission to Jupiter
- UVSP:
- UVUDF:
- UX Orionis variable:
- UXOR:
Index