Astronomy Picture of the Day

Explanation: Why do some aurorae 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 aurorae 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 colours 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 than proton aurora, and that the Earth's local magnetic field may fluctuate in unison.