This weekend marks the beginning of the end. Of winter's darkness, that is. Today (Dec. 21), the Northern Hemisphere celebrates the mark of increasingly longer days, while the Southern Hemisphere will transition to shorter days, and those at the equator won't notice much of a difference at all.
The global discrepancy in seasonal sunlight results from Earth's 23.5-degree tilt on its axis: During the
Northern Hemisphere winter
, the Earth is tilted directly away from the sun, and during the summer, it is tilted directly toward the sun. The equator does not experience much of a change during the year since it sits in the middle of the axis.