The appearance of blue clouds over Antarctica came substantially earlier this year, and had, in fact, tied for the earliest time noctilucent clouds were spotted over the South Pole since NASA first started tracking data on the clouds.
Noctilucent clouds, or night-shining clouds, usually appear in late November or early December. According to NPR, these are wispy clouds that shine a bluish-white light when viewed from the ground but appear in a far more intense shade of blue when viewed from space. About a decade ago, NASA had launched a satellite that is capable of snapping photos of the ice crystals that form these clouds and based on the space agency's data, those blue clouds appeared over Antarctica much earlier than usual, with the first sighting this year recorded in mid-November.
Satellite images posted Friday on NASA's website show that noctilucent clouds were first seen over Antarctica on November 17, and the clouds forming between that date and November 28. This is based on the agency's Aeronomy of Ice in the Mesosphere (AIM) spacecraft, which was deployed in 2007 in an effort to determine the ins and outs of this unusual event in the South Pole, and to further understand Earth's mesosphere, which can be found about 50 miles above the surface, separating our atmosphere from outer space.