Arctic and Antarctic refer to the presence or absence of what animal?

“Arctic” is from the Greek arktos, “bear,” because the constellation Ursa Major, “the greater she-bear” (also known as the Big Dipper), is always visible in the northern polar sky. “Antarctic,” therefore, literally means “opposite the bear.” By force of pure serendipity, polar bears reside at the North Pole but not the South, making the Antarctic the land without bears in more ways than one.

Source: Useless Etymology