On May 13, 1921, the first in a series of strong coronal mass ejections (CMEs), driven by a huge and complex sunspot group, reached Earth. A second followed the same day, their combined force essentially clearing the space between the Earth and Sun of interplanetary plasma. This allowed a third CME, which hit May 14, to impact Earth at full force.
Aurorae danced across the sky at remarkably low latitudes, but other effects were more grim: Communications networks were crippled, and telegraph services around the world were weakened or disabled. The geomagnetic storm is often referred to by the nickname “The New York Railroad Storm” because of its extensive interference with telephone and telegraph systems that were part of the railways in New York State; a railroad station in Brewster, New York, even burnt to the ground when the telegraph switchboard burst into flames. Similar fires were reported globally. The storm is now recognized as the most severe of the 20th century, comparable in strength to the 1859 Carrington Event.
