| R. F. Joyce Observatory | Nueva Zelanda | West Melton | — |
| Rabat Observatory | Marruecos | Rabat | — |
 Rabaul Volcanological Observatory | Papúa Nueva Guinea | — | — |
| Radcliffe Observatory | Sudáfrica | Pretoria | 1.552 m |
 Radebeul Observatory | Alemania | Radebeul | 172 m |
| Radio Neutrino Observatory Greenland | — | — | — |
 Radio Observatorio Algonquin | Canadá | Ontario | — |
| Radio Observatorio Astronómico de Sicaya | Perú | Distrito de Sicaya | — |
 RadioAstron | — | — | — |
 Radiosternwarte Kiel | Alemania | Kiel | — |
 Radolfzell bird observatory | Alemania | Radolfzell am Bodensee | — |
| Ragdon Observatory | Reino Unido | Church Stretton | — |
| Raheny Observatory | Irlanda | Dublín | — |
| Rainbow Observatory | Australia | Coonabarabran | — |
| 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 | — |
| Rezman Observatory | Eslovenia | Tunjice | — |
| Rho Ophiocus observatory | España | Las Rozas de Madrid | — |
| Ricky Observatory | Estados Unidos | Blue Springs | — |
| Ridge A | — | Región del Tratado Antártico | 4.053 m |
| Riethnordhausen Observatory | Alemania | Riethnordhausen, Saxony-Anhalt | — |
 Rihlaperä Observatory | Finlandia | Kypärämäki | — |
| Rikubetsu Astronomical Observatory | Japón | Prefectura de Hokkaido | — |
| Rimbach observatory | Alemania | Rimbach | — |
| Rio Cofio observatory | España | Collado Villalba | — |
 RIT Observatory | Estados Unidos | Nueva York | — |
 Ritter Observatory | Estados Unidos | Ohio | — |
| River Moss Observatory | Estados Unidos | Misuri | — |
| River Oaks Observatory | Estados Unidos | New Braunfels | — |
| River Ridge Observatory | Estados Unidos | Roland | — |
| Riverside observatory | Estados Unidos | Riverside | — |
| Rixeyville observatory | Estados Unidos | Rixeyville | — |
| RMS Observatory | Estados Unidos | Indian Hill | — |
| ROAD observatory | Chile | San Pedro de Atacama | — |
| ROASTERR-1 Observatory | Rumania | Cluj-Napoca | — |
| Robert Brownlee Observatory | Estados Unidos | California | — |
 Robert-Mayer-Volks- und Schulsternwarte Heilbronn | Alemania | Heilbronn | 174 m |
| Robotic Lunar Observatory | Estados Unidos | Flagstaff | — |
| Robotic Optical Transient Search Experiment | Estados Unidos | New Mexico | — |
| Rocca Observatory | Brasil | Jardim Botânico de Brasília | — |
| ROCG observatory | Brasil | Río de Janeiro | — |
| Rochedale (APTA) observatory | Australia | Rochedale | — |
| Rock Finder Observatory | Canadá | Calgary | — |
| Rockland Observatory | Estados Unidos | Sierra Vista | — |
| Roeser Observatory | Luxemburgo | Roeser | — |
| Rogers Observatory | Estados Unidos | Míchigan | — |
| Rokycany Observatory | República Checa | Rokycany | — |
| Rolling Hills Observatory | Estados Unidos | Warrensburg | — |
| Rolvenden observatory | Reino Unido | Rolvenden | — |
| Romito observatory | Italia | La Spezia | — |
| Romney Robinson Memorial Dome | Reino Unido | Condado de Armagh | — |
| ROSA observatory | Francia | Verclause | — |
| Rosarno observatory | Italia | Rosarno | — |
 ROSAT | — | — | — |
| Rose Cottage Observatory | Reino Unido | Keighley | — |
| Rose-Hulman Observatory | Estados Unidos | Terre Haute | — |
| Roseland Observatory | Reino Unido | Cornwall | — |
| Rosemary Hill Observatory | Estados Unidos | Florida | — |
| Roser observatory | España | Blanes | — |
 Rossi X-ray Timing Explorer | — | — | — |
 Rossitten Bird Observatory | Imperio alemán | Fischhausen (district) | — |
| Rotamah Island Bird Observatory | Australia | Victoria | — |
| Rothney Astrophysical Observatory | Canadá | Alberta | — |
| Rouet observatory | Francia | — | — |
| 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 | — | — |