The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission will help scientists answer questions about changes in the aurora, also known as the Northern or Southern Lights. Specifically, THEMIS investigates the nature of the events, called auroral substorms, that abruptly and explosively release solar wind energy stored within Earth's magnetotail. The THEMIS mission employs five identical spacecraft in carefully chosen orbits whose apogees line up once every 4 days over a dedicated array of ground observatories located in Canada and the northern United States.