As the snow melts and the piercing winter air begins to dull its thorns and settle into the familiar lulling whisper that comes along with rain puddles and damp earth and days that grow longer and longer and longer…let’s take a moment to think about what sort of magic brings us the tender colors of spring.
Because really, as with most things, it isn’t really magic in the sense of fairies and dragons and wizards with pointy hats—rather, it’s a natural consequence of the structure of our universe. Or, in this case, the structure of our solar system.
The Earth’s rotation axis—the axis about which the Earth spins to give us day and night, which you can think of like a skewer which penetrates our planet at the South pole and which exits at the North pole—is tilted with respect to our orbital plane around our Sun. If you hold your finger out in front of you, point it at a slight angle (so that it looks diagonal to you), and then use your hand to sort of “orbit” around the closest object in your reach, it can give you an idea of what this looks like.
Now, if you imagine the Earth, like a ball of clay encasing your finger, as it orbits around the Sun, you can conclude that at certain points of orbit, some parts of the Earth will get more sunlight than others! Intuitively, we can understand that when the North pole points towards the Sun (as much as it can), then the upper hemisphere on Earth will have more light falling onto it in comparison to whenever the North pole points away—respectively, this gives us our summer and winter seasons. The same can be said for the South pole and the lower hemisphere, remembering that the North and South pole are always in opposition, so when one points towards, the other points away.
But what causes our in-between seasons? When the Sun isn’t necessarily beating down on us for over half the day and the Earth isn’t yet buried in a thick cloud of snow, what explains the transition between the two?
Well, since the orbit of the Earth around the Sun is continuous, there must be a sort of half-way point, where one of the hemispheres doesn't really receive any more or less light than the other.
We can mark these half-way points at what are called the vernal and autumnal equinoxes—or rather, the March and September equinoxes. And in the Northern hemisphere, our beloved spring comes about in March.
The March and September equinoxes essentially occur when the Sun’s rays are directly perpendicular to the Earth’s equator—-imagine the Sun as a point and imagine a line drawn from that point to us, then the angle formed by the equator and that line would be a 90° angle at the equinoxes. And, quite fitting with their name, daytime and nighttime have around the same length!
Seasons are just one of the many consequences of the greater structure of our universe. Everything, from the shifting of the tides to the color of the sky to our mere existence, is and was a consequence of just something else—the facets of our world, all just small pieces of a much larger story.
Sources
https://www.weather.gov/lmk/seasons#:~:text=The%20earth's%20spin%20axis%20is,away%2C%20winter%20can%20be%20expected.
https://www.weather.gov/fsd/season
https://media.nationalgeographic.org/assets/reference/assets/equinox-4.pdf
