The Sun does not just shine. It throws things. A coronal mass ejection, or CME, is a massive release of plasma and magnetic field from the Sun's outer atmosphere. A single CME can carry billions of tons of material and travel at millions of kilometers per hour. When one hits Earth, it can trigger auroras, disrupt satellites, and damage power grids.

CMEs often accompany solar flares, but they are not the same thing. A flare is a burst of radiation. A CME is a burst of matter. The two can occur together, or independently. CMEs are launched when twisted magnetic field lines in the corona become unstable and snap, releasing stored energy.

Space weather forecasters watch for CMEs using satellites like SOHO and STEREO. They can see the eruption and track its path toward Earth. The warning time is usually one to three days. That is enough to shut down vulnerable systems and protect satellites, but not enough to prevent all damage.

The Carrington Event of 1859 was caused by a CME. A similar event today would cause trillions of dollars in damage. Scientists are working on better prediction and mitigation.