| Southwest Institute for Space Research | Estados Unidos | New Mexico | — |
| Sozzago astronomical Station | Italia | Sozzago | — |
 Space Research Centre, Polish Academy of Sciences | Polonia | Breslavia | — |
| Space Tracking and Communications Center, JAXA | Japón | Ibara | — |
| Spaceguard Centre | Reino Unido | Powys | — |
| Spacelab Solar | — | — | — |
| SPAG Monfrague observatory | España | Palazuelo-Empalme | — |
| SPARCS | Estados Unidos | — | — |
| SPARTAN 201-05 | — | — | — |
| Specola Solare Ticinese | Suiza | Locarno | — |
| Specula | Hungría | Eger | — |
 SPECULOOS-South Observatory | Chile | Provincia de Antofagasta | — |
 Spektr-RG | — | — | — |
 SPHEREx | Estados Unidos | — | — |
 Sphinx | Suiza | distrito de Goms | 3.571 m |
| Spica observatory | Italia | Carmignano | — |
| Spider | — | — | 36.000 m |
| Spirit Marsh Observatory | Estados Unidos | Meire Grove | — |
| SpringBok Observatory | Namibia | Khomas Region | — |
| Springe observatory | Alemania | Springe | — |
| Spurn Bird Observatory | Reino Unido | — | — |
| Squirrel Valley Observatory | Estados Unidos | Columbus | — |
| St John's Magnetic Observatory | Canadá | — | — |
| St Paul Observatory | Francia | Reunión | — |
| St-Martin Observatory | Francia | Amathay-Vésigneux | — |
 St. Andrews observatory | Reino Unido | Fife | — |
| St. George Observatory | Rumania | Cocoșești | — |
| St. Helena Magnetic Observatory | — | — | 586 m |
 St. Margarethen observatory | Suiza | Binningen | — |
| St. Mellons observatory | Gales | Cardiff | — |
| St. Michel sur Meurthe observatory | Francia | Saint-Michel-sur-Meurthe | — |
| St. Thomas Observatory | Estados Unidos | — | — |
| Staatliche Vogelschutzwarte Garmisch-Partenkirchen | Alemania | Garmisch-Partenkirchen | — |
| Stakenbridge observatory | Reino Unido | Kidderminster | — |
| Stamford observatory | Estados Unidos | Stamford | — |
| Stammersdorf observatory | Austria | Stammersdorf | — |
| Stanley Laver Observatory | Reino Unido | Pontesbury | — |
| Stansbury Park Observatory Complex | Estados Unidos | Tooele | — |
| Star Cruiser Observatory | Estados Unidos | Anza | — |
| Star Ridge observatory | Estados Unidos | Weimar | — |
 Star Square Astronomical Observatory | Japón | Shimizu-ku | — |
 Stara Lesna observatory | Eslovaquia | Stará Lesná | 785 m |
 Stardome Observatory | Nueva Zelanda | Auckland Region | — |
| Stardreams Observatory | Rumania | Vălenii de Munte | — |
| Stardust Observatory | Rumania | Brașov | — |
| Starhoo Observatory | Estados Unidos | Lakeville | — |
 Starkenburg Observatory | Alemania | Heppenheim | 256 m |
| Starkenburg Observatory Heppenheim Asteroid Survey (SOHAS) | Alemania | Heppenheim | — |