 Sears Tower – Harvard Observatory | Estados Unidos | Cambridge | — |
| Sedgefield observatory | Sudáfrica | Sedgefield | — |
| Segorbe observatory | España | Segorbe | — |
| Seismic Research Centre | Dominica | — | — |
| Seismic Station in Serra do Pilar | Portugal | Santa Marinha e São Pedro da Afurada | — |
| Seismic station Kašperské Hory | República Checa | Kašperské Hory | — |
| Seismological Observatory Gräfenberg | — | — | — |
| Seiwa Kogen Observatory | Japón | — | — |
| Selangor Observatory | Malasia | Sabak Bernam | — |
| Sencelles observatory | España | Sencelles | — |
 Sendai Astronomical Observatory | Japón | Nishikigaoka | 163 m |
| Sendai Astronomical Observatory Ayashi Station | Japón | Shimoayashi | — |
| Sendai Municipal Observatory | Japón | Sendai | — |
 Sendai Space Museum | Japón | Nagatoshi-chō | — |
| Sendling Observatory | Alemania | Sendling | 583 m |
| Senftenberger observatory | República Checa | Řeřichy | — |
| Sengamine Observatory | Japón | Kami | — |
| Serra La Nave observatory | Italia | Ragalna | 1.735 m |
| Serra Observatory | Italia | Prelo | — |
 Servicio Geológico de Canadá | Canadá | Ottawa | — |
 Servicio internacional de latitud | Estados Unidos | — | — |
| Seveso observatory | Italia | provincia de Monza y Brianza | — |
| SGT Observatory | Austria | Gaflenz | — |
| Shahe Station (Beijing Observatory) | República Popular China | Pekín | — |
| Shandong University observatory | República Popular China | Weihai | — |
| Sharjah Observatory | Emiratos Árabes Unidos | Sarja | — |
| Shasta Valley Observatory | Estados Unidos | Gazelle | — |
 Shattuck Observatory | Estados Unidos | Nuevo Hampshire | — |
| Shed of Science South observatory | Estados Unidos | Pontotoc | — |
| Sheep Hill Observatory | Estados Unidos | Boonton | — |
| Sheikh Tahir Astronomical Center | Malasia | Penang | — |
| Sheltozero Station Observatory | Rusia | Shyoltozero | 42 m |
| Shenton Park observatory | Australia | Shenton Park | — |
| Sherbrooke observatory | Canadá | Sherbrooke | — |
 Sherwood Observatory | Reino Unido | Distrito de Ashfield | — |
| Sherzer Observatory | Estados Unidos | Míchigan | — |
 Sheshan Observatory | República Popular China | Sheshan | — |
| Shimada observatory | Japón | Shimada | — |
| Shimotsuma observatory | Japón | Shimotsuma | — |
| Shinshiro observatory | Japón | Aichi Prefectural Xincheng East High School | — |
| Shishikui observatory | Japón | Shishikui | — |
| Shizuoka observatory | Japón | Shizuoka | — |
 Shosanbetsu observatory | Japón | Prefectura de Hokkaido | — |
| Shumagin Magnetic Observatory | Estados Unidos | — | — |
| Siberian State Aerospace University Observatory | Rusia | Krasnoyarsk | 160 m |
| Siding Spring Observatory: iTelescope Observatory | Australia | Siding Spring | — |
| Siding Spring-Janess-G, JAXA | Australia | Siding Spring | — |
| Siding Spring-LCO A | Australia | Coonabarabran | — |