| Snow King Observatory and Planetarium | Estados Unidos | — | — |
| Sobaeksan Optical Astronomy Observatory | Corea del Sur | Danyang | 1.378 m |
| Sobradillo observatory | España | Sobradillo de Palomares | — |
| Sodankyla Magnetic Observatory | Finlandia | Sodankylä | — |
| Soerth observatory | Alemania | Sörth | — |
 SOFIA | — | — | — |
 Sofia University Astronomical Observatory | Bulgaria | Sredets | — |
 Sohland/Spree observatory | Alemania | Sohland an der Spree | 335 m |
 SOHO | — | — | — |
| Soisy-sur-Seine observatory | Francia | Soisy-sur-Seine | — |
| Sola Fide Observatory | Estados Unidos | Condado de Mower | — |
 Solar Anomalous and Magnetospheric Particle Explorer | — | — | — |
 Solar Monitoring Observatory | — | — | — |
 Solar Observatory - Tower 2 and Tower 3 - external appearance | Austria | Treffen am Ossiacher See | — |
 Solar Observatory - Tower 4 - Appearance | Austria | Arriach | — |
 Solar Observatory Tower Meudon | Francia | Meudon | — |
| Solar Polar Orbit Observatory | República Popular China | — | — |
 Solar Probe Plus | Estados Unidos | — | — |
 Solar Radiation and Climate Experiment | Estados Unidos | — | — |
| Solar Ultraviolet Imaging Telescope | — | — | — |
| Solar-C | — | — | — |
| Solaris observatory | Polonia | — | — |
| Sollies-Pont observatory | Francia | Solliès-Pont | — |
 Sommers–Bausch Observatory | Estados Unidos | Colorado | — |
| SON Station | Chile | San Pedro de Atacama | — |
 Sonda Einstein | República Popular China | — | — |
| SONEAR Observatory | Brasil | Minas Gerais | — |
| SONEAR Observatory | Brasil | — | — |
| Sonmiani Magnetic Observatory | Pakistán | — | — |
| Sonoita Research observatory | Estados Unidos | Sonoita | — |
 Sonoma State Observatory | Estados Unidos | California | — |
| Sonoran Skies observatory | Estados Unidos | St. David | — |
| Sooke observatory | Canadá | Sooke | — |
| Sopot Astronomical Observatory | Serbia | Sopot | — |
| Sormano 2 Observatory | Italia | Villa Melzi de Eril | — |
| South African Radio Astronomy Observatory | Sudáfrica | — | — |
 South cupola of Brno Observatory and Planetarium | República Checa | Veveří | — |
| South Meridian Marker | Reino Unido | Ballyheridan | — |
| South Observatory | Reino Unido | Waterlooville | — |
 South Pole Atmospheric Research Observatory | — | — | — |
| South Wonston observatory | Reino Unido | South Wonston | — |
| Southeastern Arizona Bird Observatory | Estados Unidos | — | — |
| Southend Bradfield observatory | Reino Unido | Bradfield | — |
| Southern Photometric Local Universe Survey Telescope | Chile | — | — |
| Southern Stars Observatory | Francia | Faaa | — |
| Southern Utsunomiya observatory | Japón | Utsunomiya | — |
| Southland Astronomical Society Observatory | Nueva Zelanda | — | — |
| Southwater observatory | Reino Unido | Southwater | — |