| Mounds Observatory | Oklahoma | — |
| Mount Belleview Observatory | Canadá | — |
 Mount Cuba Astronomical Observatory | Delaware | — |
 Mount Laguna Observatory | California | — |
 Mount Lemmon Survey | Pima County | 2.791 m |
 Mount Stony Brook Observatory | Nueva York | — |
| Mount Wilson-TIE observatory | monte Wilson | — |
| Mountain Creek Ranch observatory | Arizona | — |
| Mountain Skies Observatory | Wyoming | — |
| Mountainville Observatory | Utah | — |
| MPO Observatory | Florissant | — |
| Mt. Bigelow Station 27" Telescope | Pima County | — |
| Murillo Family Observatory | San Bernardino | — |
| Murray Hill Observatory | Beaverton | — |
| NASA Orbital Debris Observatory | Cloudcroft | 2.751 m |
| NASA/MSFC ALAMO Observatory | Redstone Arsenal | — |
| Nashville observatory | Nashville | — |
| Natelli Observatory | Frederick | — |
 National Astronomical Observatory of Japan Hawaii Observatory | Hawaii County | 4.139 m |
 National Optical Astronomy Observatory | Tucson | — |
 National Radio Astronomy Observatory | — | — |
 National Solar Observatory | Arizona | — |
| Naylor Observatory | Pensilvania | — |
| Near-Earth Asteroid Tracking (NEAT) at Palomar observatory | California | — |
| Nebula Knoll Observatoy | Wakefield | — |
 NEO Surveyor | — | — |
| New Bullpen Observatory | Alpharetta | — |
| Newport Magnetic Observatory | — | — |
| NF observatory | New Mexico | — |
| NJIT Observatory | Newark | — |
| NOIRLab | — | — |
| Nora and Hashem Naraghi Hall of Science | Turlock | — |
| North Georgia Astronomical Observatory | Georgia | — |
| North Mesa Observatory | Los Álamos | — |
| North Scituate observatory | Smithville – North Scituate | — |
| Northbrook Meadow Observatory | Northbrook | — |
| Northern Arizona University observatory | Flagstaff | — |
| Northview Observatory | Mendon | — |
| Northwest Florida State College observatory | Niceville | — |
| Northwest Indiana Robotic Telescope | Lowell | — |
| Northwood Ridge Observatory | Nuevo Hampshire | — |
| Nubbin Ridge Observatory | Arkansas | — |
 NuSTAR | — | — |
 O'Brien Observatory | Marine on St. Croix | — |
 Oak Ridge Observatory | Massachusetts | — |
| Oakley Observatory | Indiana | — |
| Oakridge Observatory | The Hammocks | — |
| Oakwood observatory | Oakwood | — |