Light and lines

Have you guys ever wondred why all the continents have approximately symmetric edges..

and how they coincide with the angle of the sunlight line (or day line or whatever the scientific term is..) at the time of what is roughly the winter solstice.


(Sunlight pic via: world sunlight map)



And by the way, today is such a brilliant sun shiny day. I just cant stop feeling elated and grinning like an idiot.