Why do we have day, night and seasons?
The short answer
Day and night happen because Earth spins once every 24 hours, not because the Sun moves. Seasons happen because Earth is tilted about 23.5 degrees on its axis. When your hemisphere leans toward the Sun, sunlight strikes more directly and you get summer. Distance from the Sun has almost nothing to do with it.
The Sun does not rise, you rotate
The Sun sits where it is, shining steadily in all directions. Earth turns, once every 24 hours, carrying you from the lit side to the dark side and back. Sunrise is not the Sun climbing, it is your horizon dropping away as your part of the planet rotates into the light. Sunset is the same motion in reverse. The language we use describes the view, not the physics.
You cannot feel it because the ride is perfectly smooth
At the equator you are moving at over 1,600 kilometres per hour. You feel nothing because you only sense changes in speed, not steady motion, and Earth's rotation is extraordinarily constant. Everything moves with you: the ground, the air, the water in a glass. It is the same reason you can pour a drink on a plane at cruising altitude without noticing you are travelling at 900 kilometres per hour.
The popular explanation for seasons is wrong
Most people assume summer happens when Earth is closer to the Sun. It is a sensible guess and it is incorrect. Earth's orbit is very slightly oval, and the planet is actually at its furthest from the Sun in July, during northern summer. If distance were the cause, the entire planet would have summer simultaneously. It does not, which is the clearest evidence that something else is responsible.
The real answer is a 23.5 degree lean
Earth's axis is tilted about 23.5 degrees, and that tilt points in the same direction all year as the planet orbits. For half the year the northern hemisphere leans toward the Sun; for the other half it leans away. That is the entire mechanism. The tilt is fixed; what changes is which part of the planet is angled into the light.
Try it with a torch
Shine a torch straight down at a table and you get a small, bright, concentrated circle. Tilt the torch and the same amount of light spreads over a much larger area, so every part of it is weaker. That is exactly what the tilt does to sunlight. Direct light concentrates energy; slanted light spreads it thin. Same Sun, same output, different angle, completely different amount of heat per square metre.
The two hemispheres always disagree
Because one half tilts toward the Sun exactly when the other tilts away, the seasons are always opposite. Christmas in Australia falls in high summer. The tilt also changes how high the Sun climbs and how long it stays up: up to about 16 hours of daylight in midsummer, down to around 8 in midwinter at similar latitudes. Long bright evenings and short dark afternoons are the same tilt showing up in a different way.
Sources
Full transcript: How the Sun Creates Day, Night, and Seasons
Day, night, and seasons. Every morning the same show. The sun comes up. Every evening it goes down.
The sun rises, the sun sets. Everyone says so. But what looks suspicious. And he's right to be because the sun isn't going anywhere.
Welcome back to what and why. today. Why days happen, why nights happen, and why summer turns into winter. Spoiler.
It's not the sun moving, it's you. Here's the truth. The sun stays put, shining in every direction all the time. It's Earth that's spinning round and round once every 24 hours.
See that little dot? That's you. Right now you're on the day side. Keep spinning.
And hello night side. Nothing switched off. You just turned away. Let's watch both views at once.
In space. Your dot crosses into the sunlight. On the ground. That exact same moment looks like sunrise.
The sun didn't climb. You roll toward it. Sunset is the same trick in reverse. The sun never moves.
Your horizon does. But wait, you say, if Earth is spinning, why can't I feel it? Because it's the smoothest ride there is. You're moving at more than a,000 km hour right now.
But the speed never changes. There are no bumps, and everything spins along with you. Even the water in a glass, not a ripple. Now, seasons.
Most people guess summer is when Earth swings closer to the Sun. Sounds sensible, and it's wrong. Surprise! In July, northern summer, Earth is actually at its farthest from the sun all year.
So, if it's not distance, what is it? It's this. Our planet is tilted 23 1/2° like it's leaning back in a chair. And as Earth travels around the sun, that tilt keeps pointing the same way all year long.
That little lean changes everything. Why does a tilt matter? Try this with a flashlight. Point it straight down.
A small bright hot spot. Now slant it. The same light spreads out into a big weak puddle. Direct light is strong.
Slanted light is gentle. Remember that. So when your half of Earth is tilted toward the sun, sunlight hits you almost straight on. Flashlight pointed down.
Strong heat, long days, summer. 6 months later, your half tilts away. The very same sunlight arrives slanted and weak. Winter, same sun, different angle.
And here's the twist. The two halves of Earth always disagree. When the north is tilted away, bundled up in winter, the south is tilted toward, splashing at the beach. Christmas in Australia, that's high summer.
Opposite halves, opposite seasons. The tilt does one more trick. It changes the sun's path across your sky. In summer, the sun climbs high and stays out long, up to 16 hours of daylight.
In winter, it sneaks along low and clocks out early, sometimes just 8. Long, bright evenings or early cozy nights. That's the tilt, too. Remember, the sun doesn't rise or set.
You spin once a day. You can't feel it because the ride is perfectly smooth. And the seasons, not distance, the tilt. Next time we zoom in on the sun itself and discover it has weather, dark spots, and giant eruptions.
See you on What and Why.
Transcript of the episode, lightly cleaned for readability.
Sample question
Question 1 of 10
What causes day and night?
- Earth rotating once every 24 hours correct
- The Sun orbiting the Earth
- The Moon blocking sunlight
- Earth's tilt
Sunrise and sunset are the result of your part of the planet rotating into and out of sunlight.
That is one of 10. The rest are not shown here, and the answer order changes every time you take the quiz.
Written by Watt & Why. Published 10 October 2026. Last reviewed 17 October 2026.