During the deep winter months in the Antarctic when the sun is well below the horizon, clouds can be seen to glow when the moon is high in the sky. On average the temperature at the Amundsen-Scott South Pole Station during the winter months can drop to below minus 60 degrees Celsius. With temperatures being well below freezing, clouds comprise only of ice crystals. In the absence of light, these ice clouds remain hidden in the night sky, but when the moon is high and bright, the ice crystals within the cloud scatter the moonlight making the cloud glow (Photos 1 and 2).
Photo (1) Moonlight scattering through a low ice cloud making it appear to glow. The moon is behind the structure on the right. (Photograph taken during the 1991 Antarctic winter at the Amundsen-Scott South Pole Station. Courtesy of John KW Chan, HKO)
Photo (2) Photograph taken during the 1991 Antarctic winter at the Amundsen-Scott South Pole Station. (Courtesy of John KW Chan, HKO)