| Abbreviation | Definition |
|---|---|
| MSSS | Maui Space Surveillance Site |
| MST | Mean Solar Time |
| MSTO | Main Sequence Turn-Off |
| M-TYPE | Metallic (Asteroid) |
| MUAAC | McMaster Undergraduate Academic Astronomy Club |
| MUF | Mysterious Unknown Force |
| MVAC | Mission Valley Astronomy Club |
| MVEMJSUN | Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus & Neptune |
| MVEMJSUNP | Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto |
| MW | Milky Way |
| MWO | Mount Wilson Observatory |
| N | Nitrogen |
| NA | Negative Alignment |
| NA | Non-Anomalous |
| NAAP | Nebraska Astronomy Applet Project |
| NAC | National Astronomy Consortium |
| NAIC | National Astronomy And Ionosphere Center |
| NAM | National Astronomy Meeting |
| NAO | National Astronomical Observatory |
| NAO | National Astronomy Olympiad |