| Blue Canyon observatory | Estados Unidos | Blue Canyon | — |
| Blue Mesa Observatory | Estados Unidos | New Mexico | — |
| Blue Mountains Observatory | Australia | Leura | — |
| Blåvand Fuglestation | Dinamarca | Varde | — |
| Boambee observatory | Australia | Boambee | — |
 Bobergs observatorium | Suecia | municipio de Estocolmo | — |
| Bobergs observatory, Skansen | Suecia | municipio de Estocolmo | — |
| Boca Raton Observatory | Estados Unidos | Boca Raton | — |
| Bocholt observatory | Alemania | Bocholt | — |
| Bochum Observatory | Alemania | — | — |
 Bohnenberger Observatorium | Alemania | Calw | — |
 Boleslav Tecla Observatory in Moravská Třebová | República Checa | Moravská Třebová | 412 m |
| Bollwiller observatory | Francia | Bollwiller | — |
| Bologna Observatory | Italia | Bolonia | — |
| Boltwood Observatory | Canadá | Stittsville | — |
| Bolzaneto observatory | Italia | Bolzaneto | — |
 BOOMERanG experiment | — | — | — |
| Bootes Observatory | España | Boecillo | — |
| BOOTES-2 Observatory | España | Algarrobo | — |
 Bordeaux Observatory | Francia | Floirac | — |
| Borken observatory | Alemania | Borken, North Rhine | — |
| Bornheim observatory | Alemania | Bornheim | — |
| Borok Magnetic Observatory | Rusia | — | — |
| Borowiec Astrogeodynamic Observatory | Polonia | Borówiec | — |
 Bosianu Astronomical Observatory | Rumania | Bucarest | — |
 Boswell Observatory | Estados Unidos | Nebraska | — |
| BOSZA Observatory | Hungría | Distrito de Pécs | — |
 Bothkamp Observatory | Alemania | Schleswig-Holstein | — |
| Boulder Geomagnetic Observatory | Estados Unidos | Boulder | — |
| Boulder Knolls observatory | Estados Unidos | Hidden Meadows | — |
| Boulder Magnetic Observatory | Estados Unidos | — | — |
 Bowman Observatory | Estados Unidos | Connecticut | — |
| Boyeros Observatory | Cuba | La Habana | — |
 Brackett Observatory | Estados Unidos | Claremont | — |
| Bradbury observatory | Reino Unido | Stockton-on-Tees | — |
| Bradley Observatory | Estados Unidos | Georgia | — |
| Bradstreet Observatory | Estados Unidos | Pensilvania | — |
| Braeside Observatory | Estados Unidos | Flagstaff | 2.152 m |
| Brandon Magnetic Observatory | Canadá | — | 380 m |
| Bray-et-Lû observatory | Francia | Bray-et-Lû | — |
 Brazil National Observatory | Brasil | Vasco da Gama | — |
| Bredenkamp Observatory | Alemania | Bremen | — |
| Breitenweg observatory | Alemania | Bergisch Gladbach | — |
| Brelingen observatory | Alemania | Wedemark | — |
| Bremen observatory | Alemania | Bremen | — |
| Brescia observatory | Italia | Brescia | — |
 Breslau observatory | Polonia | Breslavia | — |
| Brignoles observatory | Francia | Brignoles | — |