| Roving observer | Chile | — | — |
| Royal Park observatory | España | Riells | — |
 Rožňava observatory | Eslovaquia | Rožňava | — |
| Runcorn observatory | Reino Unido | Halton | — |
| Rushay Farm Observatory | Reino Unido | Sturminster Newton | — |
| Rusty Mountain Observatory | Estados Unidos | Queen Valley | — |
| Rutherford observatory | Estados Unidos | Nueva York | — |
 Rutherfurd Observatory | Estados Unidos | Manhattan | — |
 Rybachy Biological Station | Rusia | Rybachi | — |
| Ryubangtaek Science Museum | Corea del Sur | Inji-myeon | — |
| Réseau de surveillance volcanologique et sismologique de Mayotte | Francia | — | — |
| S.O.S. observatory | Estados Unidos | Minneapolis | — |
| Saarbruecken Rastpfuhl observatory | Alemania | Sarrebruck | — |
| Sabah State al-Biruni Observatory | Malasia | Sabah | — |
| Sabino Canyon Observatory | Estados Unidos | Tucson | — |
| Sable Island Magnetic Observatory | Canadá | Nueva Escocia | 5 m |
| SADR observatory | Chile | Río Hurtado | — |
| Saguaro Observatory | Estados Unidos | Tucson | — |
| Saint Barthelemy observatory | Italia | Aosta | — |
| Saint Petersburg Magnetic Observatory | Rusia | — | — |
| Saint-Caprais observatory | Francia | Rabastens-de-Bigorre | — |
| Saint-Felicien observatory | Canadá | Saint-Félicien | — |
 Saint-Malo marigraph | Francia | Saint-Servan | — |
| Saint-Saturnin-les-Avignon Observatory | Francia | Saint-Saturnin-lès-Avignon | — |
| Saint-Sulpice Observatory | Francia | Saint-Sulpice | — |
| Sainte Helene Observatory | Francia | Sainte-Hélène | — |
| Sainte-Clotilde observatory | Francia | Reunión | — |
| Sakai Observatory | Japón | Sakai | — |
| Sakamoto Hachiryu Observatory | Japón | prefectura de Kumamoto | — |
| Sakamoto Observatory | Japón | Ōtsu | — |
| Saku observatory | Japón | Saku | — |
 Sakurajima Volcano Research Center | Japón | Sakurajima Yokoyama-chō | — |
| Salida observatory | Estados Unidos | Salida | — |
 Saltsjöbaden Observatory | Suecia | provincia de Estocolmo | 50 m |
| Salvador astronomical observatory | Argentina | Asociación Atlética Estudiantes | — |
| Salvatore di Giacomo observatory | Italia | Nápoles | — |
| Salvia Observatory | Francia | Saulges | — |
| Samford Valley Observatory | Australia | Samford | — |
| San Benedetto Po observatory | Italia | San Benedetto Po | — |
| San Clemente observatory | Estados Unidos | San Clemente | — |
| San Costantino observatory | Italia | San Costantino | — |
| San Defendente Observatory | Italia | San Defendente | — |
| San Emigdio Peak observatory | Estados Unidos | California | — |
| San Fernando Magnetic Observatory | España | — | — |
| San Gabriel Observatory | España | Alicante | — |
| San Juan Magnetic Observatory | Estados Unidos | — | — |
| San Lazzaro di Savena observatory | Italia | Ponticiella | — |
| San Marco Observatory | Italia | Salerno | — |