Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2000 May 19 An Aurora Before the Storm Credit & Copyright: Jan Curtis (U. Alaska), ACRC

Explanation: Early April brought some of the most intense auroral storms this decade. An aurora on April 6 was reported to be the largest visible on Earth since 1989, and was seen throughout Europe and much of northern North America. On that day, many skywatchers expecting to see a rare alignment of planets were treated to a additional treat. Many reported aurorae with a relatively unusual red colour. The above aurora recorded at dusk over Alaska sported the more typical green glow. A huge auroral ring can be seen superposed above trees and a building. Auroral activity occurs high in the Earth's atmosphere and is a direct result of storms on our Sun. As huge sheets of charged particles stream out from the Sun, a small fraction of these particles are funneled in by Earth's magnetic field and strike atoms high in the atmosphere, causing the sky to glow. The particles are harmless to people on Earth's surface, but can cause havoc on satellites in orbit far above.