| Stixendorf observatory | Austria | Stixendorf | — |
 Stjerneborg | Suecia | Municipio de Landskrona | — |
| Stockholm Observatory | Suecia | provincia de Estocolmo | — |
| Stockport observatory | Australia | Stockport County Football Club | — |
| Stokesville Observatory | Estados Unidos | Virginia | — |
| Stone Edge observatory | Estados Unidos | El Verano | — |
| Stone Finder Observatory | Canadá | Calgary | — |
| Stonegate Observatory | Estados Unidos | Ann Arbor | — |
 Stonehenge Aotearoa | Nueva Zelanda | Carterton District | — |
 Stony Ridge Observatory | Estados Unidos | California | 1.730 m |
 Stonyhurst Observatory | Reino Unido | — | — |
| Stowupland observatory | Reino Unido | Stowmarket | — |
 Stratoscope | — | — | — |
| Strawberry Field observatory | Reino Unido | City of Southampton | — |
| Student Astronomical Observatory, Department of Astronomy - Plana | Bulgaria | Stolichna obshtina | — |
| Stull Observatory | Estados Unidos | Nueva York | — |
| Stuttgart-Hoffeld observatory | Alemania | Stuttgart | — |
| Submillimeter Array, Mauna Kea (SMA) | Estados Unidos | Hilo | — |
 Submillimeter Wave Astronomy Satellite | Estados Unidos | — | — |
| Sudair Observatory | Arabia Saudí | Provincia de Riad | 915 m |
 Sudbury Neutrino Observatory | Canadá | Ontario | — |
| Sukagawa observatory | Japón | Sukagawa | — |
| Sulphur Flats observatory | Estados Unidos | Jémez Springs | — |
 Sulphur Mountain Cosmic Ray Station | Canadá | Improvement District No. 09 (Banff National Park) | — |
 Sultan Ismail Building | Malasia | Kota Iskandar | — |
| Sumoto observatory | Japón | Sumoto | — |
 Sun Dagger site | Estados Unidos | condado de San Juan | — |
| Sun Watcher using Active Pixel System Detector and Image Processing | — | — | — |
| Sundre bird observatory | Suecia | — | — |
| Sunflower Observatory | Estados Unidos | Olathe | — |
| Sunflower Observatory | Estados Unidos | Regal Santa Fe | — |
| Sunhill Observatory | Estados Unidos | Newton | — |
| Sunrise | — | — | — |
| Sunriver Nature Center observatory | Estados Unidos | Sunriver | — |
 Sunriver Observatory | Estados Unidos | Oregón | — |
| Sunspot Solar Observatory | Estados Unidos | condado de Otero | — |
| Suntopia Marina observatory | Japón | Sumoto | — |
| SUNY Oneonta College Observatory | Estados Unidos | Nueva York | — |
 Super-Kamiokande | Japón | Hida | — |
| Supernova/Acceleration Probe | — | — | — |
| Sura Gardens | Ucrania | Kam'yanka | — |
| Surlari Magnetic Observatory | Rumania | Ilfov | 84 m |
| Surlari National Geomagnetic Observatory | Rumania | — | — |
| Sutherland Observatory | Sudáfrica | Karoo Hoogland | — |
| Sutherland-LCO A | Sudáfrica | Karoo Hoogland | — |
| Sutherland-LCO Aqawan A #1 observatory | Sudáfrica | Sutherland | — |
| Sutherland-LCO B | Sudáfrica | Karoo Hoogland | — |
| Sutherland-LCO C | Sudáfrica | Karoo Hoogland | — |