Glossaire beginning with I
Angle between the plane of an orbit and the ecliptic.
- Interstellar (matter)
- Gas and dust filling the Milky Way between the stars. This is the material from which stars, planets and comets form.
- Atomic nucleus containing a different number of neutrons than the main nucleus, the number of protons remaining the same. Example: 3He, is the rare isotopic nucleus of helium, with one neutron and 2 protons, instead of 2 neutrons and 2 protons for the abundant species 4He.