Plasma
Definition
The fourth state of matter — a gas of charged particles — making up the Sun, solar wind, and aurora environment.
In plain language
Heat a gas enough and electrons break free from atoms, creating a soup of charges that responds to magnetic fields. Almost everything in the aurora story — the corona, the solar wind, the magnetosphere — is plasma.
The science
Plasmas exhibit collective behavior: quasi-neutrality, wave modes, and frozen-in magnetic flux under ideal MHD. Space plasma dynamics — reconnection, wave-particle interactions — govern all auroral energy transfer.
Why it matters for aurora viewing
Auroras are plasma physics made visible: understanding that charged gas follows magnetic rules explains nearly every behavior you'll observe.
See this in action on tonight's data.