A geomagnetic storm is a temporary disturbance of Earth's magnetosphere caused by solar wind structures like coronal mass ejections (CMEs) and corotating interaction regions, with their frequency rising and falling alongside the 11-year sunspot cycle. When these solar structures hit Earth, they compress the magnetosphere and weaken the dayside magnetic field, driving intense electric currents in the magnetosphere and ionosphere that trigger phenomena such as auroras at unusually low latitudes, radio and radar disruptions, and geomagnetically induced currents (GICs) that can damage power grids. The most extreme recorded event, the Carrington Event of 1859, set fire to parts of the fledgling US telegraph network and shocked operators, while a 1989 storm caused a massive blackout across Quebec and produced auroras visible as far south as Texas. Scientists measure storm intensity using the Dst index, which tracks the storm's three phases—initial, main, and recovery—and classify it as moderate, intense, or a super-storm, with the U.S. NOAA also rating it on a G-scale from G1 to G5. These powerful space weather events highlight the critical link between solar activity and modern technological infrastructure.