M numbers;0; 
Magnetic field;95; 
Magnetosphere;169; 
Magnitude;242; 
Main sequence star;417; 
Main sequence;295; 
Mantle;538; 
Mass;616; 
Matter;659; 
Meridian;751; 
Messier catalogue;900; 
Meteorite;1017; 
Meteors;1123; 
Methane;1255; 
Milky Way system;1435; 
Milky Way;1323; 
Molecule;1508; 
Month;1558; 
Moon;1635; 
Motion;1708; 
Mounting;1822; 
NASA;1865; 
Navigation;1960; 
Nebula;2098; 
Neutrino;2216; 
Neutron star;2393; 
Neutron;2289; 
Newton;2497; 
NGC number;2668; 
NGC;2550; 
Night shadow;2766; 
Nova;2840; 
Nuclear fusion;2958; 
Nucleus;3066;