Picture of the Sun taken from Moscow. Photo courtesy of

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.

: layer of the sun above the photosphere, usually only visible during a solar eclipse

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.

Last modified: Thursday, 8 September 2011, 8:57 AM