The dramatic beginning, or "onset," of an auroral substorm is displayed in this image of Earth
acquired from high above Earth's Northern Hemisphere. The northern auroral oval is located in the center of
the image, while the bright dayside of Earth is located below it. The bulge of bright intensities
corresponding to the onset of the auroral display occurs in the auroral oval near local midnight over
northern Norway and Sweden. A coastline map has been superposed on the image. This image was acquired by the
Earth Camera on board the Polar spacecraft at 20:59 UT on April 3, 1996. At the time, the spacecraft
had passed apogee and begun its descent toward perigee. The spacecraft was positioned at an altitude of
48,280 km and the geographic latitude and longitude was 57.7° and 62.1°, respectively.
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