April 30: A solar wind stream that hit Earth's magnetic field during the weekend sent Northern Lights spilling over the Canadian border into the continental USA. "Magnificent May Day auroras lit up the night sky over Chippewa Falls, Wisconsin, on May 1st and into the wee morning hours of May 2nd," reports Tony Wilder.

Southern Lights: The solar wind impact sparked auroras over both ends of the planet. "After a slow start to the aurora observing season, we are finally getting some beautiful Aurora Australis here at the geographic South Pole (90 degrees S. latitude)," reports J. Dana Hrubes, science leader at the Amundsen-Scott Station. He took the picture above at the peak of the geomagnetic storm on May 1st. At this location the sun set on March 23rd and will not rise again until six months later.

The solar wind continues to blow at high speed, and NOAA forecasters estimate a 50% chance of more geomagnetic activity during the next 24 hours. High latitude sky watchers should remain alert for aurora.

What is a geomagnetic storm?
The Earth's magnetosphere is created by our magnetic field and protects us from most of the particles the sun emits. When a CME or high-speed stream arrives at Earth it buffets the magnetosphere.

If the arriving solar magnetic field is directed southward it interacts strongly with the oppositely oriented magnetic field of the Earth. The Earth's magnetic field is then peeled open like an onion allowing energetic solar wind particles to stream down the field lines to hit the atmosphere over the poles.

At the Earth's surface a magnetic storm is seen as a rapid drop in the Earth's magnetic field strength. This decrease lasts about 6 to 12 hours, after which the magnetic field gradually recovers over a period of several days.

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