| Mountain Skies Observatory | Estados Unidos | Wyoming | — |
| Mountainville Observatory | Estados Unidos | Utah | — |
| MPO Observatory | Estados Unidos | Florissant | — |
| Mr. Barclay’s observatory | Reino Unido | Essex | — |
 Mt Etna Volcano Observatory | Italia | — | 2.940 m |
| Mt. Bigelow Station 27" Telescope | Estados Unidos | Pima County | — |
| Mt. Guizi observatory | República Popular China | Hongshan | — |
| Mt. Kajigamori observatory | Japón | Ōtoyo | — |
| Mt. Ohdu Unification Observatory | Corea del Sur | Paju | — |
| Mueggelheim observatory | Alemania | Parada de tranvía Müggelheimer Straße/Wendenschloßstraße, Berlin | — |
| Muensterschwarzach Observatory | Alemania | Schwarzach am Main | — |
| Mui Observatory | Japón | — | — |
 Mukai Chiai Children's Science Museum | Japón | Tatebayashi | — |
 Mullard Radio Astronomy Observatory | Reino Unido | Harlton | — |
| Multa Observatory | Rusia | Multa | — |
| Mundenheim observatory (1907-1913) | Alemania | Ludwigshafen | — |
| Munich observatory (1819-1938) | Alemania | Múnich | — |
| Murcia Observatory | España | Murcia | — |
| Murillo Family Observatory | Estados Unidos | San Bernardino | — |
| Murou observatory | Japón | Emperador Uda | — |
| Murray Hill Observatory | Estados Unidos | Beaverton | — |
| Murrumbateman observatory | Australia | Murrumbateman | — |
| Murviel-les-Montpellier observatory | Francia | Murviel-lès-Montpellier | — |
 Museo del Espacio de Hong Kong | República Popular China | Hong Kong | — |
 Museo La Specola | Italia | Padua | — |
 Muses B | — | — | — |
| Muxagata Observatory | Portugal | Vila Nova de Foz Côa | — |
 Mykolaiv Observatory | Ucrania | Mykolaiv | 52 m |
 Mårtsbo observatory | Suecia | Municipio de Gävle | — |
 Mühlenturm | Alemania | Rees | — |
| N.P. Wieth-Knudsen Observatory | Dinamarca | Gribskov | — |
| Nachi-Katsuura Observatory | Japón | Prefectura de Wakayama | 10 m |
| Nagano Observatory | Japón | Ōmachi | — |
| Nagatoro observatory | Japón | Nagatoro | — |
| Nagycenk Magnetic Observatory | Hungría | — | — |
 Nahal Oz Observers Memorial Monument | Israel | — | — |
| Nakagawa observatory | Japón | Anan | — |
| Nakagoya Astronomical Observatory “Subaru Dome” | Japón | prefectura de Miyazaki | — |
| Nakanoshima Observatory | Japón | prefectura de Kagoshima | — |
| Nanchuan observatory | República Popular China | Tianhe | — |
| Nankivell Observatory | Nueva Zelanda | Carterton District | — |
| Nanshan Station, Xinjiang Observatory | República Popular China | Urumqi | — |
| Nanyo Observatory | Japón | Prefectura de Yamagata | 252 m |
 Nançay Decameter Array | Francia | — | — |
 Nançay Radio Observatory | Francia | Nançay | — |
 NAOJ Mizusawa Campus | Japón | Ōshū | — |
| Narama observatory | Polonia | Narama | — |
| Narsarsuaq Magnetic Observatory | Groenlandia | — | — |