Soon it will be that time of the year again, in which we take our thick winter coat, a beanie and the winter boots out of the closet. The days will become shorter and the nights colder. The good thing about it though, we can start going sleighing, build snowmen, go skiing and of course, start snowball fights with our friends. For me personally, it is the best time of the year but I know many people who dislike winter very much, especially because of the cold temperatures. The question that crosses my mind every now and then though is why it only really starts being cold in winter and why summer is always considered to be the warm season. Lucky for us, I found the answers to these questions and will explain them in the following paragraphs.
Before we start digging into further detail of the explanation of the seasons, there are two important things to keep in mind. The first thing is that the seasons on both halves of the earth are always opposite to each other. This means that when it is winter in the northern hemisphere, the southern hemisphere is already enjoying summer. The second important aspect is that the earth doesn’t sit straight in space, instead, it sits at an 23.5-degree angle, resulting in the earth being tilted to one side.
Now that you have these two facts in mind, we can have a look at the explanation.
Since the sun is the heat source for our planet, a lot of people believe that the reason to why the temperature changes between summer and winter has something to do with the distance between the earth and the sun. This would imply that in summer, the earth is close to the sun, which results in warmer temperatures, whereas in winter, the sun is further away from our planet, making it colder. In reality, it is exactly the opposite. In July (summer), the earth is the furthest away from the sun and in January (winter), the earth is the closest to the sun.
We have already figured out that the axis of the earth is tilted by 23.5 degrees. We also know that the earth travels around the sun, which takes 365 days. When you now combine these to aspects, it makes it clear that while the earth is on its travel journey around the sun, some parts of the earth’s surface are pointing directly at the sun at different times.
When the northern hemisphere is pointed towards the sun, the sun rays hit the earth more directly and warm up this part of the earth, which means that the light can’t spread out as much and therefore increases the amount of energy that shines on any given spot, resulting in warmer temperatures (summer).
When the northern hemisphere is pointed away from the sun, the sun rays hit the earth at an angle, which means that their impact is not as strong as if they would come in straight. The light is therefore more spread out and the amount of energy that hits the earth at any given spot is lower, resulting in lower temperatures (winter).
On the southern hemisphere, it is always the other way around so if the northern hemisphere is pointed towards the sun (summer), the southern hemisphere is pointed away from the sun (winter) and vice versa.
Generally said, for both hemispheres applies that in winter, the sun rays hit the hemisphere at a shallow angle (→ lower temperatures) and in summer, the sun rays hits the hemisphere at a steep angle (→ warmer temperatures).
So the answer as to why it gets cold in winter is short and simple: It is because of the tilt of the earth’s axis by 23.5 degrees.
Sources:
https://www.childrensmuseum.org/blog/why-winter-cold-and-summer-hot (Children’s Museum, November 15th, 2022)
https://www.loc.gov/everyday-mysteries/meteorology-climatology/item/why-is-it-hot-in-summer-and-cold-in-winter/ (Science Reference Section, Library of Congress, November 15th, 2022)