HOBART, Australia - 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 degrees Fahrenheit. A weather balloon measured temperatures at minus 189 degrees Fahrenheit on the day the photos were taken. Resembling airborne mother-of-pearl shells, the clouds are produced when fading light at sunset passes through water-ice crystals...