Lyma - maps
- Lyman alpha
- Lyman alpha forest
- Lyman beta
- Lyman continuum
- Lyman series
- M dwarf stars
- M giant stars
- M magnitude
- M regions
- M stars
- M subdwarf stars
- M subgiant stars
- M supergiant stars
- macro spicules
- macroturbulence
- Magellanic clouds
- Magellanic stream
- magnetic anomalies
- magnetic disturbances
- magnetic fields
- magnetic monopoles
- magnetic poles
- magnetic properties
- magnetic stars
- magnetic storms
- magnetic variable stars
- magneto optical effects
- magnetographs
- magnetoheliographs
- magnetohydrodynamics
- magnetosphere
- magnetospheric substorms
- magnitudes
- mainsequence
- mainsequence stars
- major axis
- major merger
- Maksutov telescopes
