As Arctic regions descend into darkness this winter, some beautiful natural phenomena will brighten up the sky. Auroral activity can be expected, as solar wind particles rain through the atmosphere, but occasionally more rare phenomena can appear.
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In these stunning photos, strange iridescent features formed over the northern Norwegian town of Tromsø on Dec. 16, much to the delight of photographer Truls Tiller.
"Here the sun is gone for now," Tiller told SpaceWeather.com, "but this beautiful view makes the winter darkness nice to be in as well. The picture was taken at 10.30 am, in the middle of the ‘day.'"
Known as polar stratospheric clouds (or PSCs), these clouds form in the stratosphere at approximately 15 miles in altitude. "Regular" grey-white clouds that we are more accustomed to are found lower in the troposphere at between 3 to 6 miles in altitude.
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Because PSCs are so high, they are composed of ices in an environment where temperatures can drop to -85 degrees Celsius (-121 degrees Fahrenheit). Then, should the angle of the sun be just right (below the horizon), an amazing light-show may commence. The twilight skies over Tromsø seem to have been just perfect for this festive display.
Understandably, PSCs are also known as "mother of pearl" clouds as the tiny ice particles (only ~10µm across) strongly diffract sunlight, producing extremely vivid colors that outshine ordinary iridescent clouds that can be found all over the world. Although they are indeed beautiful, according to SpaceWeather.com, PSCs are thought to be related to destruction of ozone and implicated in the formation of ozone holes at high latitudes.
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