THEMIS observations confirm for the first time that magnetic reconnection in the magnetotail triggers the onset of substorms. Substorms are the sudden violent eruptions of space weather that release solar energy trapped in the Earth's magnetic field. Note: THEMIS reconnection animation Animator: Walt Feimer (HTSI). Scientist: Vassilis Angelopoulos (University of California, Berkeley). Platforms/Sensors/Data Sets: THEMIS.