01
June vs December
Jump between the two solstices. Earth's axis keeps pointing in the same direction in space while the Northern Hemisphere alternately leans toward and away from the Sun.
Earth · Question
Interactive seasons simulator: why Earth has seasons
Earth is actually a little closer to the Sun during Northern Hemisphere winter. Seasons come from the 23.5° axial tilt, not distance. Move through the year, jump to solstices and equinoxes, then switch the tilt to 0° and compare.
Visual model
Earth's axis points the same way all year.
Northern hemisphere
Summer
MarJunSepDecMar
23.5° tilt: seasonal contrast changes as Earth orbits the Sun.
Try the simulator
Test the two explanations for seasons.
A useful model should let you test the common "distance" explanation against the axial-tilt explanation.
02
Set axial tilt to 0°
With no axial tilt, the strong seasonal pattern disappears in this model even though Earth's distance from the Sun still changes through the orbit.
03
Check the distance claim
Earth reaches perihelion in early January, during Northern Hemisphere winter. That is the opposite of what "closer means summer" predicts.
Orbit & tilt · reference
Season markers and Earth–Sun distance.
Dates vary slightly from year to year. The key comparison is that Northern Hemisphere summer occurs near Earth's farthest point from the Sun, while Northern winter occurs near its closest point.
| Point in year | Typical timing | Earth–Sun distance | What it demonstrates |
|---|---|---|---|
| March equinox | About March 20 | Near 1 AU | Neither hemisphere is tilted strongly toward the Sun; day and night are roughly equal in length. |
| June solstice | About June 20–21 | Near 1.016 AU | Northern Hemisphere has its longest daylight even though Earth is close to aphelion. |
| Aphelion | Early July | ~152.1 million km · ~1.017 AU | Earth is farthest from the Sun during Northern Hemisphere summer. |
| September equinox | About September 22–23 | Near 1 AU | The hemispheres again receive similar day length. |
| December solstice | About December 21–22 | Near 0.984 AU | Northern Hemisphere has its shortest daylight even though Earth is close to perihelion. |
| Perihelion | Early January | ~147.1 million km · ~0.983 AU | Earth is closest to the Sun during Northern Hemisphere winter. |
Season questions
Why tilt matters more than distance.
Q1
Does Earth's distance from the Sun cause the seasons?
No — not the familiar opposite seasons of the two hemispheres. Earth's slightly elliptical orbit does change incoming solar energy, but it affects the whole planet at once. Axial tilt changes both sunlight angle and day length in opposite ways between the hemispheres, which is the dominant seasonal effect.
Q2
Why does a 23.4° tilt matter so much?
When a hemisphere tilts toward the Sun, sunlight arrives more directly and the Sun stays above the horizon longer each day. When it tilts away, the same solar energy is spread over a larger surface area and daylight is shorter.
Q3
What if Earth had no axial tilt?
The strong tilt-driven seasonal cycle would largely disappear. Earth's eccentric orbit would still produce a smaller global annual change in incoming solar energy, so real temperatures and weather would not become perfectly constant.
What's simplified
This is a teaching model, not an ephemeris.
01
Orbit shape
The display treats Earth's orbit as essentially circular so the tilt geometry stays readable. Earth's real orbit is a slight ellipse, which is why perihelion and aphelion exist.
02
Visual emphasis
The screen layout emphasizes the direction of Earth's axis and the Sun–Earth geometry. Do not read the on-screen distances, sizes, or tilt drawing as a scale diagram.
Misconception check
Quick check.
Quick check
Go deeper
Keep exploring.
Next in this series →
Moon phases ↗
Sun-Earth-Moon 3D orbital geometry.
Orbits
Gravity and orbits
Connect the yearly orbit used here to the gravity that keeps planets moving around the Sun.
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Back to the interactive 3D solar system.