| U green frog observatory | República Checa | Ondřejov | — |
| U. of Minn. Infrared Observatory | Estados Unidos | Mount Lemmon | — |
| UAdeC observatory | México | Saltillo | — |
| UAS-ISON Observatory | México | Sinaloa | — |
| Uccle Solar Equatorial Table | Bélgica | Uccle | — |
 UCL Observatory | Reino Unido | Municipio de Barnet | — |
| Udaipur Solar Observatory | India | Udaipur | — |
| Uenohara Observatory | Japón | Uenohara | 747 m |
| UFES astronomical observatory | Brasil | Vitória | — |
| Uiterstegracht Station | Países Bajos | Leiden | — |
| UJA Observatory | España | Jaén | — |
| ULTRA Observatory | República Popular China | Gusu | — |
 Ultraviolet Explorer | Estados Unidos | — | — |
| Umbrella Observatory | Alemania | Fredenbeck | — |
| Umeenosato Observatory Tenkyukan | Japón | prefectura de Oita | — |
| UMS Labuan Tower | Malasia | Labuan | — |
| Undelivered observatory in Vysluní | República Checa | Výsluní | — |
| Underground Neutrino Observatory | — | — | — |
| Underwood observatory | Estados Unidos | Hubbardston | — |
| UniBRITE | — | — | — |
| United States Naval Observatory Flagstaff Station | Estados Unidos | Flagstaff | 2.273 m |
| Universidad de Monterrey observatory | México | Nuevo León | — |
| University Hills observatory | Estados Unidos | California | — |
 University of Alabama Observatory | Estados Unidos | Tuscaloosa | — |
| University of Central Arkansas Observatory | Estados Unidos | Conway | — |
| University of Maryland Observatory | Estados Unidos | Maryland | — |
| University of Minnesota observatory | Estados Unidos | Minneapolis | — |
| University of Narino Observatory | Colombia | Provincia de Pasto | — |
| University of New Hampshire Observatory | Estados Unidos | Nuevo Hampshire | — |
| University of North Alabama Planetarium and Observatory | Estados Unidos | Alabama | — |
| University of North Dakota observatory | Estados Unidos | Grand Forks | — |
| University of Oklahoma Observatory | Estados Unidos | Oklahoma | — |
 University of Reading Atmospheric Observatory | Reino Unido | Earley | — |
| University of Rhode Island observatory | Estados Unidos | Quonochontaug | — |
| University of Southern Queensland observatory | Australia | Greenmount | — |
 University of Tartu Old Observatory | Estonia | Tartu (municipio) | — |
| University of the Andes station | Venezuela | Mérida | 3.600 m |
| University of Toronto Southern Observatory | Canadá | — | — |
 Universitäts-Sternwarte München | Alemania | Múnich | — |
| Universitätssternwarte Graz | Austria | Styria | — |
| Untermenzing Observatory | Alemania | Múnich | — |
| Uppsala Magnetic Observatory | Suecia | — | — |
| Uppsala observatory | Suecia | — | — |
| Uppsala-Angstrom observatory | Suecia | Upsala | — |
 Urania | Austria | Innere Stadt | 165 m |
 Urania Observatory | Dinamarca | Aalborg | — |
| Urania public observatory | Bélgica | Hove | — |
 Urania Sternwarte | Suiza | Zúrich | — |
 Uraniborg | Reino de Dinamarca | Municipio de Landskrona | — |
| Uraniborg Observatory | España | Écija | — |
 Ursa Observatory | Finlandia | Helsinki | — |
| Urumqi Magnetic Observatory | República Popular China | — | — |
| USAF Academy Observatory | Estados Unidos | Colorado Springs | — |
 Ussuriysk Astrophysical Observatory | Rusia | Ussuriysk | 274 m |
| Usuda Star Dome | Japón | Prefectura de Nagano | — |
| Uto Observatory | Japón | Uto | — |
| UTP astronomical observatory | Colombia | Pereira | — |
| Utsunomiya observatory | Japón | Utsunomiya | — |
| Utsunomiya-Imaizumi observatory | Japón | Utsunomiya | — |
| UWA observatory | Australia | Crawley Town Football Club | — |
 UWS Rotary Observatory | Australia | New South Wales | — |
| UZAYMER Observatory | Turquía | Sarıçam district | 130 m |
 Uzhhorod Observatory | Ucrania | Úzhgorod | 183 m |
| Uzurano observatory | Japón | Kasai Station | — |
 Úpice observatory | República Checa | Úpice | 415 m |
 Ústecká hvězdárna | República Checa | Telnice | 480 m |