The Earth is a fascinating planet; showcasing four different seasons that provide vastly different climates and environments over its 365-day cycle. If you’ve ever wondered why the Earth has different seasons, you’ll be glad you dropped by as this is the topic we will be taking a closer look at today.
So, why does the Earth have different seasons? The Earth has different seasons due to its orbital patterns, angular tilt, and position in relation to the Sun. The season that one hemisphere experiences in relation to the other do not occur due to proximity alone; it has to do with the angle of the Sun’s rays that it receives.
The interesting thing about living on Earth is that no matter where you are, or when you’re reading this, you’re never more than three months away from a change of seasons.
Spring, Summer, Fall, and Winter are all experienced in both the Northern and Southern Hemispheres (and the region in between!)
While conditions may vary, every region experiences differences from a stable environment and climate year around.
And why is this?
Let’s take a closer look.
What Causes Seasons On Earth
To answer this question, we need to zoom way out and begin with a top-down look at the Earth’s orbit around the Sun.
The earth spins on its axis, at a fixed angle of about 23 ½ degrees.
And as the Earth goes around the Sun, once every 365.25 days, this axial tilt, or obliquity, changes the exposure to the sun’s radiation that different parts of the Earth experience at any given time.
Remember, at the same time Earth is rotating on its axis once every day (causing day and night).
The Earth remains in a fixed tilted position in the same direction all year round as we orbit the Sun but that means the Sun’s light shines differently on Earth at different times of the year.
Understanding the seasons is therefore all about understanding angles. Its about how each Hemisphere is angled toward/away from the Sun.
So when it’s winter in the Northern Hemisphere, the North Pole tips away from the Sun.
This means that sunlight strikes the Northern Hemisphere at a shallow angle for a short period of time.
This is why winter weather is generally cool with short days and long nights.
The same is true in reverse, so the same thing occurs if you view the same scenario from the perspective of the Southern Hemisphere.
As Earth orbits the Sun the Northern Hemisphere moves towards spring.
During spring, the Earth is tilted neither toward nor away from the Sun, and day and night are about equal in length.
As we make our way to the summer months, the Earth is still tilted in the same direction but now it’s on the other side of the orbit.
The North Pole is tipping toward the Sun and sunlight strikes the Northern Hemisphere more directly.
The Sun stays in the sky for a longer time compared to winter and days are warmer.
Notice too that while it’s summer in the Northern Hemisphere it’s winter in the Southern Hemisphere.
This is because of Earth’s tilt; the seasons are reversed.
It’s important to deconstruct a common misconception here.
People often think is that they believe that the hemisphere that’s tilted toward the Sun experiences summer because it’s closer, and therefore experiences more of the heat. This notion is actually incorrect.
If this was the case, it would be Summer in America and Australia at the same time; which we know does not happen in reality.
In actuality, there’s a relatively small difference between the Earth’s closest and furthest points from the Sun.
Interestingly and quite surprisingly, those of you in the Northern Hemisphere might be surprised to learn that Earth is actually 5 million kilometers closer to the Sun in January than it is in July.
So the difference doesn’t have to do with your hemisphere’s proximity to the Sun.
It has to do with the angle of the Sun’s rays that it receives.
Why Seasons Have Different Climates
So by now, we know that it is the impact of direct/indirect sunlight that causes the seasons. So what difference does direct or indirect sunlight make?
It basically defines the environment and climate a hemisphere receives.
Let’s take a look at a simple experiment. You can imagine how it works by taking a piece of paper and a flashlight.
If you imagine that the paper is Earth’s surface, where the flashlight is instead the light of the Sun.
If you was to shine the flashlight directly onto the paper at a 90-degree right angle, you would see a perfectly formed circle. The light is shining directly and all of the energy is concentrated in one area.
However if you was to tilt the flashlight (changing the angle that the paper receives the light), then you would notice that the circle would change into an Ellipse.
Here the light is shining indirectly, and the same amount of energy is spread out over a larger area.
So in a particular point on the paper it feels colder in the indirect light than in the direct light.
It’s important to note that the amount of energy from the flashlight (aka Sun) is always the same. It’s not changing.
However, if it’s spread out over a larger area, we feel it less. Let’s take a look at what this means for the Earth.
Say its June in the Northern Hemisphere; the region is angled towards the Sun. If we shine the flashlight directly on the Northern Hemisphere, we see it illuminates a certain area.
But if we moved the flashlight to shine indirectly on the Southern Hemisphere, we see that it’s illuminating a larger area,
just like we discussed above.
It is this effect, added to the fact that higher Sun angles result in longer days, that more energy is ultimately heating a particular hemisphere at any one time.
Depending on the angular tilt of each hemisphere, one would experience summer and the other winter.
So pulling it all together, when the Northern Hemisphere is tilted towards the Sun, it’s receiving direct sunlight. It feels warmer, which means it’s summer there.
And the Southern Hemisphere is receiving indirect sunlight, which means it feels cooler. That’s winter.
Six months later, when the Earth is on the other side of the Sun, we have the opposite.
What About The Equator?
Now we can understand how it works for the Northern and Southern Hemisphere, you’re probably wondering what happens to countries and regions around the Equator.
You probably already know that they experience hotter climates and more stable weather year-round?
People near the equator experience stable temperatures (and barely notice the seasons at all) because they receive roughly the same amount of light all year around.
This is due to the angular tilt and the way the Sun’s light hits this landmass on Earth. It’s why it’s renowned for being so hot!
The poles, on the other hand, feel the difference in a huge way. The Earth’s 23 ½ degree tilt ensures that they never point directly at the Sun. They spend around half of the year with more daylight and the other with more darkness.
So the best way to truly understand it, is to think about how your hemisphere is leaning towards or away from the Sun.
The important thing to remember, for the seasons at least, is that the Earth is tilted at an angle of 23.5 degrees.
So when the Earth is on one side of the Sun, the Northern Hemisphere is angled away from the Sun, and The Southern Hemisphere is angled toward the Sun.
Ultimately when a hemisphere is angled towards the Sun, the Sun’s rays hit it directly.
But when a hemisphere is angled away from the Sun, the Sun’s rays hit it indirectly.
It is the impact of direct/indirect sunlight that causes the seasons!
Hey, my name is Chris. I’m a passionate and seasoned astronomer who loves nothing more than observing the night sky. I also love researching, learning, and writing all things Space and the Universe. I created Astronomy Scope to share my knowledge, experience, suggestions, and recommendations of what I have learned along the way while helping anyone to get into and maximize their enjoyment of the hobby.