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.
2015 June 1
Pulsating Aurora over Iceland 
Video Credit & Copyright: Stéphane Vetter (Nuits sacrées); Music: Eric Aron
Explanation: Why do some auroras pulsate? No one is sure. Although this unusual behavior has been known for a long time, the cause remains an active topic of research. Featured here is a dramatic video that captured some impressive pulsating auroras in mid-March over Svínafellsjökull Glacier in Iceland. The 48-second video shown is not time-lapse. The real-time pulsations are exemplified by sequences where the astrophotographer is visible moving about in the foreground. A close inspection of the enigmatic flickering sky colors reveals that some structures appear to repeat, while others do not. The quick rapidity of the pulsations seen here is somewhat unusual -- more common are aurora with pulsations that last several seconds. Recent research shows that pulsations are more common in electron-generated aurora, rather thanproton aurora, and that the Earth's local magnetic field may fluctuate in unison.

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Tomorrow's picture: comet polaris

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