Some of the coldest temperatures on Earth brought a rare cloud formation to the skies over Antarctica, scientists said Tuesday.
Meteorological officer Renae Baker captured spectacular images of the nacreous clouds, also known as polar stratospheric clouds, last week at Australia's Mawson station in Antarctica.
The clouds only occur at high polar latitudes in winter, requiring temperatures less than minus 176 Fahrenheit. A weather balloon measured temperatures at minus 189 Fahrenheit on the day the photos were taken.
Resembling an airborne mother-of-pearl shell, the clouds are produced when fading light at sunset passes through water-ice crystals blown along a strong jet of stratospheric air more than six miles above the ground.
"Amazingly, the winds at this height were blowing at nearly 230 kilometers (143 miles) per hour," Baker said on the Australian government's Antarctic Division's Web site.
Australian Antarctic Division atmospheric scientist Andrew Klekociuk said the clouds are seldom seen, but are occasionally produced by air passing over polar mountains.
"You have to be in the right part of the world in winter, and have the sun just below your horizon to see them," he said.