![A display of aurora australis, or southern lights, manifesting itself as a glowing loop, in an …[Credits : NASA/Johnson Space Center/Earth Sciences and Image Analysis Laboratory]](http://media-2.web.britannica.com/eb-media/12/76812-004-EEA8843E.jpg)
A display of aurora australis, or southern lights, manifesting itself as a glowing loop, in an image of part of Earth’s Southern Hemisphere taken from space by astronauts aboard the U.S. space shuttle orbiter Discovery on May 6, 1991. The mostly greenish blue emission is from ionized oxygen atoms at an altitude of 100–250 km (60–150 miles). The red-tinged spikes at the top of the loop are produced by ionized oxygen atoms at higher altitudes, up to 500 km (300 miles).
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