Astronomical Unit: Distance from Earth to the Sun; about 150 million kilometers.
Aurora Borealis: Atmospheric phenomenon in Earth's magnetosphere. Aurora Borealis is located in the northern hemisphere.
Aurora Australis: Atmospheric phenomenon in Earth's magnetosphere. Aurora Australis is located in the southern hemisphere.
Black hole: the result of a massive star collapsing. Gravity acts so strongly on black holes that nothing can escape it.
Brown dwarf: Collection of matter that could not achieve nuclear fusion.
Chromosphere: layer of the sun above the photosphere, usually only visible during a solar eclipse
Coronoa: outermost layer of the sun's atmosphere
GigaYear (Gyr): 1 billion years
Main Sequence: Longest part of a star's lifespan. Stars with larger mass have shorter main sequences. Stars with smaller mas have longer main sequences.
Photosphere: visible surface of the sun
Protostar: cloud of gas that is beginning the process of nuclear fusion.