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Auroras
Series of photos during an aurora substorm that lasted about 25 minutes, in central Alaska. As the display intensified, the snow took on a green appearance.
Views:
The beautiful and often eerie curtains of light in the nighttime sky known as aurora have been enjoyed by people for millennia. Auroras are glowing streaks in the sky seen at night in the far north and south. They are popularly called northern lights (officially called "Aurora borealis" in the northern hemisphere, and "Aurora australisis" in the southern). During this luminous meteoric phenomenon, colorful light appears in streams, ascending toward the zenith from a dusky line or bank, a few degrees above the polar horizon; when reaching south beyond the zenith, it forms what is called the corona, about a spot in the heavens toward which the dipping needle points. Occasionally the aurora appears as an arch of light across the heavens from east to west. Sometimes it assumes a wavy appearance, and the streams of light are then called merry dancers. They assume a variety of colors, from a pale red or yellow to a deep red or blood color.
"Aurora Borealis", the scientific name of the aurora of the northern hemisphere, means "northern dawn". Originating in an atmospheric layer high above the surface of the earth, the northern lights can be seen during dark hours in the northern hemisphere.
The light is emitted when charged particles from the sun are guided by the earth's magnetic field into the atmosphere near the poles. When the particles contact atmospheric molecules, primarily oxygen and nitrogen, at altitudes from 300 down to 100 km, a part of the energy of the collisions transforms to visible light.
What do auroras look like from space?
Two views from the Space Shuttle of the Aurora Australis or Southern Lights (location unknown). At left, a sinuous looping band of airglow above the Earth Limb. At right, a spiked band of red airglow called a "Red Crown" above the Earth Limb. Both auroras are around 80 - 120 km above the surface of the earth.
