This week, an emergency crew will fly to Antarctica to evacuate an expeditioner—in the dark. A medical emergency is under way involving someone at McMurdo Station, Antarctica's largest research station; the victim is believed to be a US citizen and is currently in stable condition. But the timing is bad, since it's currently winter in Antarctica—which means no daylight for six months, although there is "some twilight at midday," according to a spokesperson for the US National Science Foundation, which oversees McMurdo. The station is the US Antarctic Program's hub, CNN reports. (More Antarctica stories.)