| Rainwater Observatory and Planetarium | Estados Unidos | Misisipi | — |
| Ralph A. Worley Observatory | Estados Unidos | Luisiana | — |
| Ramonville Saint Agne observatory | Francia | Ramonville-Saint-Agne | — |
| Rancho Del Sol observatory | Estados Unidos | Camino | — |
| Rancho Palos Verdes observatory | Estados Unidos | Rancho Palos Verdes | — |
| Rand II Observatory | Estados Unidos | Lake Placid | — |
| Rand Observatory | Estados Unidos | Nueva York | — |
| Rani Observatory | Estados Unidos | San Diego | — |
| Rantiga observatory | Italia | Carpineti | — |
| Rantiga Observatory | Italia | Tincana | — |
| Rapid City observatory | Estados Unidos | Rapid City | — |
| RAS Observatory, Biggera Waters | Australia | Biggera Waters | — |
| RAS observatory, Moorook | Australia | Moorook | — |
| RAS Observatory, Officer | Australia | Officer | — |
| RASC Observatory | Estados Unidos | Alder Springs | — |
| RaSo Observatory | Alemania | Röhrsdorf | — |
| Rattle Snake Observatory | Estados Unidos | Smithton | — |
| Ray Observatory | Japón | Toyoura | — |
| Rayleigh Observatory | Reino Unido | South Woodham Ferrers | 75 m |
| RDSS observatory | Rusia | Rostov del Don | — |
 Real Instituto y Observatorio de la Armada | España | provincia de Cádiz | — |
 Real Observatorio de Bélgica | Bélgica | Uccle | — |
 Real Observatorio de Edimburgo | Reino Unido | City de Edimburgo | — |
 Real Observatorio de Greenwich | Reino Unido | Municipio de Greenwich | 68 m |
 Real Observatorio de Madrid | España | Madrid | 655 m |
 Real Observatorio del Cabo de Buena Esperanza | Sudáfrica | Ciudad del Cabo | 15 m |
| Red Barn Observatory | Estados Unidos | Georgia | — |
| Red Buttes Observatory | Estados Unidos | Laramie | 2.246 m |
| Red de Vigilancia Espacial de los Estados Unidos | Estados Unidos | Maui County | — |
 Red Global de Telescopios del Observatorio Las Cumbres | Estados Unidos | Goleta | — |
| Red Mountain Observatory | Estados Unidos | Utah | — |
| Redondo Beach observatory | Estados Unidos | Redondo Beach | — |
| Redshed observatory | Austria | Johann Weirether | — |
 Reform Tower, Meethill, Invernettie | Reino Unido | Aberdeenshire | — |
 Regiomontanus-Sternwarte | Alemania | Núremberg | 338 m |
| Reilhanette Observatory | Francia | Reilhanette | — |
| Reintal observatory | Alemania | Múnich | — |
| Remains of Astronomical Observatory at Penllergaer | Reino Unido | Swansea | — |
| Remeis Observatory | Alemania | Bamberg | — |
| Remote Integrated Telescope Zentrum | Chile | — | — |
 Remplin Observatory | Alemania | Malchin | 9 m |
| Requena observatory | España | Requena | — |
| Resolute Bay Magnetic Observatory | Canadá | — | — |
| Resse Observatory | Alemania | Wedemark | — |
| Retamar observatory | España | Retamar y el Toyo | — |
 Reutlingen Observatory and Planetarium | Alemania | Reutlingen | 385 m |
 Reuven Ramaty High Energy Solar Spectroscopic Imager | — | — | — |
| Reynolds Observatory | Estados Unidos | Nueva York | — |