A. During the 24-hour darkness of the austral autumn and winter, the South Pole Telescope operates nonstop under impeccable conditions for astronomy.

B. The atmosphere is thin (the pole is more than 9,300 feet above sea level, 9,000 of which are ice), stable (due to the absence of the heating and cooling effects of a rising and setting Sun) and the pole has some of the calmest winds on Earth, blowing almost always from the same direction.

C. “The South Pole has the harshest environment on Earth, but also the most benign,” says William Holzapfel, a University of California at Berkeley astrophysicist, the on-site lead researcher at the South Pole Telescope.

D. From an astronomer’s perspective, not until the Sun goes down and stays down—March through September— does the South Pole get “benign.”