Photographer Valerie Pond took some great photos of the aurora over Yellowknife, Northwest Territories, early Saturday.

The temperature at the time was -2f with windchill of -18f.

According to the Geophysical Institute at the University of Alaska Fairbanks, the aurora is a luminous glow of the upper atmosphere, caused by energetic particles that enter the atmosphere from above.

The composition and density of the atmosphere and the altitude of the aurora determine the possible light emissions. The colors that we see are a mixture of all the auroral emissions. Just like the white sunlight is a mixture of the colors of the rainbow, the aurora is a mixture of colors. The overall impression is a greenish-whitish glow. Very intense aurora gets a purple edge at the bottom.

Valerie's Flickr page

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