The episode now called the Carrington Event remains the benchmark for an extreme geomagnetic storm. The geomagnetic storm that followed was driven by magnetized material expelled from the Sun, now understood as a coronal mass ejection, or CME. A modern grid has its own version of the telegraph problemA geomagnetic storm does not need to strike a transformer like lightning. On NOAA’s G1-to-G5 geomagnetic storm scale, a G5 event can produce widespread voltage-control and protection problems. Utilities and satellite operators nevertheless have time to staff control rooms, adjust grid configurations, postpone risky maneuvers and place spacecraft into safer modes.