Whether you love swimming in the summer, crunching colorful leaves in the fall, making snowmen in the winter, or seeing beautiful flowers blossom in the spring, you know that there are four seasons that everyone on the Earth experiences. Even if it doesn’t snow where you live, or if it’s always sunny, the seasons mark big changes in each year, for many reasons.   

But did you know that, while North Americans enjoy the summer sun, many South Americans are actually experiencing the snow? Or that a day in the North and South Pole last for 6  whole months? 

Welcome to the first installment of the Science Behind the Everyday series, where we’ll be exploring the fascinating science behind things that happen to Earth every day. From weather to waves to moon phases, we’ll be learning about how the things you’re familiar with on a daily basis really work.  

As you probably have guessed by now, this article is a brief introduction to the four seasons and why they happen! 

23.5° 

The four seasons happen because of one main reason – the Earth is tilted at an angle of 23.5°. To picture this, imagine a ball with a stick poked all the way through it. Now, imagine yourself grabbing the stick by both ends so it points straight up and down. Then, tilt it slightly to the right. The stick you imagined is like the axis that the Earth spins around. When it orbits around the sun, the Earth is also rotating around this axis at a slight angle of 23.5°. See the picture below! 

More sunlight

The two diagrams above are good ways to see why the 23.5° tilt of the Earth causes the four seasons.  

The first image shows how the Earth’s tilt causes different amounts of sunlight to hit it. When the Earth is tilted like this, the northern hemisphere, or the part of the Earth north of the equator, gets more light than the southern hemisphere, or the part south of the equator. Because the north gets more direct light, it gets hotter. This causes it to be summer. The south, on the other hand, gets less sunlight. So it gets colder, which causes it to be winter.  This is why people in North America are experiencing summer while many people in South America are in the winter! 

The second image shows the Earth orbiting around the sun, and how the seasons change when it’s at different positions. When the Earth is on the left, it’s summer in the northern hemisphere and winter in the southern hemisphere. The opposite is true when the Earth is on the right! And, when the Earth is in those middle positions, both the northern and southern hemispheres get the same amount of direct sunlight. This is the spring and the fall! The reason why it feels colder or warmer in the spring or the fall isn’t actually because of the amount of sunlight you’re getting – it's because of other factors, like the oceans and the land.  

Polar night and midnight sun 

Imagine a day where the sun doesn’t set after 24 hours… instead, it takes 50 days to set! This is what happens in many places in the Arctic and Antarctic Circles, which are regions close to the north (Arctic) and south (Antarctic) poles. Because of the Earth’s 23.5° tilt, the Arctic and Antarctic circles either get constant sunlight or hardly any at all. When the sun is up for more than 24 hours, it's called midnight sun. And when it’s nighttime for longer than 24 hours, it’s called polar night.  In Kiruna, Sweden, polar night lasts for 28 days, followed by midnight sun for 50 days. That’s 28 days straight of no sun and 50 days straight of the sun! Even more amazing – at the North and South Poles, polar night and midnight sun each last for 6 full months! (See below for some pictures of Kiruna, Sweden)