City lights weren’t the only thing shining in the night sky on October 29, 2003. A spectacular display of the aurora borealis, or northern lights, blazed across a large swath of the Northern Hemisphere that night as a powerful solar storm buffeted the Earth with a wind of electrically charged particles. Some of the particles get trapped in Earth’s magnetic field and are funneled along magnetic field lines toward the geomagnetic poles. When the particles strike the outer atmosphere, they cause a colorful light display.
Normally, these light spectacles are limited to very high latitudes, but when powerful solar storms occur, as they did during the last week of October, the aurora can creep down from the poles and can be visible across Europe and the United States. In this image of part of eastern North America captured by the Defense Meteorological Satellite Program on the night of October 29, the bright white veil of the southward-dipping aurora is visible all across southern Canada and the northern U.S. Dotted across the scene are the city lights from major urban areas in the region.
Although the unusual auroras that occur with heightened solar activity are a treat for backyard star gazers, they have a downside as well. All that electromagnetic activity can disrupt power grids and satellites that provide everything from TV to cellular phone signals.