The Arctic Circle - Theory Vs. Reality

The Arctic Circle is one of those imaginary lines of geographic significance. In theory, on December 21, the sun will make a cursory appearance on the horizon at noon. All places further north will be in 24 hours of darkness. Conversely, on June 21, the sun will simply appear to bounce against the horizon at midnight, and all places to the north will get the midnight sun.

Of course, this is the hypothetical ideal. Reality is not quite that tidy, because our sun appears in the sky as a disk, not a point source of light, so the 'line' is actually a band 100km across.

In addition, the earth has all sort of wiggles and wobbles as it goes about its business of spinning around on its axis and around the sun. Even the spinning isn't constant: the earth spins a tad more slowly every year due to Tidal Acceleration. The more you read about it, the more you think that all cartographers must go bald from pulling out their hair, trying to create fixed reference points on a planet that constantly changes and shifts.