Auroras: billboards for electric space

  The Roman goddess of dawn.
People living in the arctic regions can witness the aurora - beautiful shimmering curtains of light appearing in the night sky. Auroras are like giant advertisements for the existence of Electric Space; the world's largest neon-like billboards. They are named after the Roman goddess of dawn.

Spectacular auroras are phenomena whose beauty almost defies description. Triggered by disturbances in the solar wind and Earth's magnetosphere, these curtains of light occur when high energy electrons and ions in the magnetotail are energized and are guided towards the polar regions by Earth's magnetic field. At about 70 miles above the surface, fast moving electrons encounter Earth's upper atmosphere, where they slam into gas molecules, making them glow: oxygen molecules glow whitish-green, nitrogen molecules glow pink. Contrary to popular belief, auroras do not produce any sounds.

  A view of the Southern Lights taken from the Space Shuttle Discovery in 1991. Photo courtesy NASA.
NASA's Discovery astronauts got a great look at the aurora's "curtains" in 1991. This photo of the aurora was taken from the orbiting space shuttle several hundred miles above Earth's South Pole.

Satellites that orbit thousands of miles above Earth's surface can provide a global view of the aurora that neither the Space Shuttle nor ground observations can. These photographs show that the light of the aurora forms an oval shape — like a crown of light — high above and surrounding Earth's magnetic poles. The auroral oval or zone expands and contracts over a period of hours and days, depending on geomagnetic activity. The auroral zone is about six degrees wide, centered on a magnetic latitude of 67°.
  A photograph of the auroral oval taken by the Dynamics Explorer - 1 satellite. Courtesy of Louis Frank, University of Iowa.

Auroras act as a gauge of what's happening to Earth's magnetic field tens of thousands of miles away. On days that are calm, auroras are only slightly visible, even in the northern latitudes. But during magnetic storms, the auroral oval can grow until it can be seen as far south as Colorado or even Florida.


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