Astrophysics (index)


(non-metallic element, He, atomic number 2.)

Helium (He) is the element with atomic number 2, symbol He. Its most common isotope and has atomic weight 4, but atomic weight 3 is also stable.

It is the second most common element, about 24% of the observable universe by mass (Helium Abundance). A bit is the result of nuclear Fusion of Hydrogen in stars, but most helium was formed in conditions shortly after the Big Bang. The initially-very-hot universe descended through Temperatures that produced a particular ratio of neutrons and protons, which at a cooler temperature, combined into light-weight isotopes, including a very stable helium isotope (atomic weight 4), much of which remained as the temperature cooled further.

Helium has a Metastable State of Excitation with one electron excited and of opposite the typical spin. It can remain in this state for a couple of hours and on relaxing, produces an Emission Line of about 80830 Angstroms.


Referenced by:
Asymptotic Giant Branch (AGB)
Alpha Process
Bose-Einstein Statistics
Carbon Star
CNO Cycle
Energetic Neutral Atom (ENA)
Gas Giant
Giant Planet
Hayashi Track
Horizontal Branch (HB)
Helium Flash
Helium Rain
Helium Runaway Shell
HI Region (HI)
Ice Giant
Intracluster Medium (ICM)
Low Mass Star
Main Sequence Star
Metallicity (Z)
Planetary Nebula (PN)
Proton-Proton Chain
Solar Energetic Particle (SEP)
Supernova (SN)
Spitzer Space Telescope (SST)
Stellar Age Determination
Thermal Pulse
Triple Alpha Process
White Dwarf
Wolf-Rayet Star