The Science of Seasons

Sometimes, in the middle of what feels like a record-breaking heat wave, I start wondering about seasons. I recall fond memories of when the outdoor temperatures were cold enough that the wind brought tears to my eyes and the tears froze on my face. Good times.

But seriously, what is up with such big variations in temperature? Why do people in different parts of the world experience seasons at different times and with different fluctuations in temperature? Why do some places seem to have no temperature fluctuations at all?

The answer to all of these questions can be found in the sciences of meteorology and climatology. These fancy science words mean the study of temperature and weather patterns on a short time scale (meteorology) or a longer one (climatology).


Why do we have seasons?

Overall, our experience of seasons depends on how close we are to the sun at any given time. Because the Earth spins on a tilted axis (like an off-centered top), the distance from any point on Earth to the sun varies over the course of a year. We experience the hottest weather, or summer, during times of the year when our part of Earth is pointed towards the sun.  When our part of the Earth is pointed away from the sun, then we experience cold weather, or winter.

Interestingly, this also explains why temperatures at locations near the North and South Pole have such big fluctuations. During the times of year when these locations are pointed away from the sun, they are VERY FAR from the sun, and experience almost no direct warming. Temperatures in Antarctica (at the South pole) can reach as low as -76 degrees Fahrenheit!  Even more shocking is the fact that there is almost complete darkness at the North and South Poles during the winter months, because their geographic location prevents them from being exposed to sunlight.

Don’t worry, though! Summer months at the North and South Poles have sunlight around the clock for the entire season. That’s right: it never gets dark during those months. Just imagine how hard it must be to convince little kids that it is “absolutely, definitely” bedtime, all while the sun is still shining brightly in the sky.


Why do some places have more moderate seasons?

For those of us who don’t live at the North or South Pole, though, our seasons are more moderate. In New England, for example, the daylight is shorter and temperatures are colder in the winter months, but we still have some daylight and some sunlight-induced warmth, even on the coldest blizzard days. While our summer days have more sunlight and are warmer, there is still some darkness at night, even in the middle of July.

As we get closer and closer to the Equator (the big “belt” around the middle of the Earth), we see less and less temperature variations between different seasons. In fact, many locations near the equator are hot all year long! Why is this? Well, because of the tilt of the Earth, more direct sunlight reaches locations close to the equator, making them hot, hotter, and extremely hot. Are you wondering how hot? Average annual temperatures (over the course of a whole year) are close to 90 degrees Fahrenheit, and summer temperatures climb well over 100 degrees! There have been actual reports of people frying eggs on the sidewalk (more accurately, metal pots that heat up in direct sunlight), just using that kind of summer heat. Thankfully most of us have air conditioning!


Why do some places have Spring and Autumn (Fall)?

So we’ve talked so far about two seasons, summer and winter, but what about the other two? First of all, lots of places on Earth really only experience two seasons, summer and winter! But most of us are lucky enough to live in places with four seasons, because we live in temperate latitudes, meaning locations that are not too close to the Poles and not too close to the Equator.

So for those of us who experience the other two seasons, let’s talk about them. Both of these seasons start when the sun is shining directly over the Equator. On March 20th, the Earth experiences what we call the “Vernal Equinox,” which is a fancy way of saying that spring starts in the Northern Hemisphere and fall starts in the southern hemisphere. In September, the “Autumnal Equinox” occurs, which means that fall starts in the Northern Hemisphere and spring starts in the Southern Hemisphere.

Spring has some advantages, scientifically, including the increased hours of sunlight, the fact that many plants starts to flower in this time, and the fact that animals and birds who migrate during the colder months can now return. Speaking of birds, did you know that birds can fly as fast as 30 miles per hour? And that their winter migration can be over tremendous distances (up to 16,000 miles)?? That’s even farther than the distance between New York City and Sydney!


What causes leaves to change color?

What about the final season, Fall (or Autumn)? In New England, this season is characterized by lots and lots of colorful leaves, which occur because these leaves stop producing chlorophyll, which is a green material that the leaves use to make food. Once that green color starts to fade, we can see the other colors that appear.

OK, but why do only some locations, such as New England, have very brightly colored fall leaves? Well, the combination of cold and sunny days (common in New England falls) causes the leaves to keep producing the other pigments, or colored materials. Too much rain, on the other hand, will cause all of the pigments to stop being produced, leading to leaves that turn brown rather than red, yellow, or orange.

This is your moment of science about seasons, with a suggestion to remember these crazy hot days of summer all through the next ice-cold winter!


Author: Mindy Levine



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