Why Does Earth Have Seasons?

Why does Earth have seasons (winter, summer, fall, spring)?  The common misconception is that Earth has seasons due to Earth's changing distance from the Sun.  The Earth's path around the Sun over the course of the year is not a perfect circle.  It's slightly elliptical.  As a result, there are times when Earth is closer to the Sun and times when it is farther away from the Sun.  We are all well aware that if you bring your hand closer to a hot stove or fire it feels warmer and if you pull your hand away it feels cooler.  Therefore, common sense might tells us that yes, distance is the reason for the seasons.  Unfortunately this is incorrect.  The variation between farthest away and closest to the Sun is about 1.5%, so the difference in distance is not that great.  It's certainly not great enough to cause the seasons.  There are also a couple of common sense arguments you can use to debunk the myth that changing distance causes seasons.

1.  When the United States and all of Earth's northern hemisphere experiences summer, Australia and all of Earth's southern hemisphere experience winter.  If distance is the reason for the seasons, how is it possible for it to be summer in one hemisphere and winter in the other hemisphere?

2.  Earth is closest to the Sun in January and farthest from the Sun in July.  It's closest to the Sun in winter for the northern hemisphere and farthest during summer.  This fact alone should convince everyone that distance is not the answer.

So what does cause the seasons?  The cause of the seasons is Earth's 23.5 degree tilt of its axis.  In the image below you can see that Earth is tilted slightly on its side.

NASA Space Place [CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)]

Notice in this image that the north pole of Earth always faces in the same direction.  As the Earth moves around the Sun, the hemisphere that is tilted toward the Sun changes.  In the northern hemisphere's summer, the northern hemisphere is tilted toward the Sun.  In the winter, it is tilted away from the Sun.  There's still a bit of a misconception here.  When people here the words 'tiled toward' and 'tilted away' they often still walk away with the impression that the northern hemisphere is slightly closer/farther away from the Sun than the southern hemisphere.  That is true, but again the difference in distance is so small that it plays no significant role in the seasons.

The tilt causes one hemisphere of Earth to receive more directly sunlight (more energy) than the other hemisphere. 

Whenever a portion of Earth receives more directly sunlight, it receives more energy and temperatures increase giving us summer.  When a portion of Earth receives less sunlight, it receives less energy and temperatures decrease, giving us winter.

Now you know the truth.  Earth's seasons have nothing to do with distance and everything to do with the tilt of Earth and the directness of sunlight.  When your kids ask you about the seasons you can now tell them the truth and be confident in it.