Many skywatchers who went outside to view the moon, Mars, Jupiter, and Saturn grouped together last night were treated to a bonus spectacle -- a surprise auroral display.
According to reports sent to Sky & Telescope and also collected at the Auroral Activity Observation Network, the dramatic red display was visible across Europe and seen as far south as New Mexico and Florida.
The shock wave of solar wind hit the Earth at about 12:40 p.m. EDT and the visible display lasted until about 10:30 p.m. EDT.
Auroras most often glow green, the color emitted by oxygen atoms high in the upper atmosphere after they are struck by bombarding electrons from Earth's magnetosphere.
Red displays are rarer, sometimes involving energized nitrogen molecules lower down in the atmosphere -- an indication of a more potent geomagnetic storm. Auroras that extend away from the poles and closer to the equator, as occurred last night, also reflect strong storm conditions.
According to Cary Oler of Solar Terrestrial Dispatch, "Although there will probably be some residual substorm activity over the higher latitudes during the next 24 hours, there will not be a recurrence of the auroral storming for most middle-latitude locations."