An Epic View of the Seasons

What happened

As a result, the Northern and Southern Hemispheres receive almost the same amount of sunlight, and day and night are nearly equal in length. NASA Earth Observatory/Michala Garrison Most kids learn in elementary school that the seasons are caused by Earth rotating on a tilted axis during its yearly orbit around the Sun.

The substantial tilt, about 23.5 degrees, is thought to be the result of an ancient planetary body, Theia , smashing into Earth about 4.5 billion years ago, in the same cataclysmic collision that formed the Moon . To visualize why Earth has seasons, imagine the planet as a spinning top tilted to one side .

The most striking difference is between the two solstices. In December, South America lies near the center of the disk and much of Antarctica is visible, while North America is partially out of view.