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.
What changes at 40° north and 40° south?
With the same modeled Earth position and axial tilt, compare the Sun's height at local solar noon and the approximate hours of daylight. These two measurable outcomes change together with tilt.
40° N
40° S
02 / Stand on the surface
What would a one-metre pole show at noon?
Keep the same Earth position and tilt above. Stand on level ground at 40° N or 40° S and compare the shadow cast by a vertical 1-metre pole.
Geometric illustration from the existing spherical-Earth 40° latitude model; the Sun icon, pole drawing and terrain are not to scale. Shadow length = pole height ÷ tan(noon solar elevation). Not a local weather, terrain, seasonal temperature or daily sun-path forecast. NASA Earth Facts.
June solstice, 23.5° tilt · the subsolar point is near 23.5° N. This is a geometric model, not temperature or weather.
Simplified spherical Earth at 40° latitude, level horizon, no atmospheric refraction, daylight computed from solar declination. Daylight lengths and angles are approximate, not site-specific forecasts. NASA Earth facts.
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.
Teacher quick use
Test the “distance causes seasons” idea.
A short classroom prompt using the same model students just explored.
- Learning objective
- Explain how axial tilt changes sunlight angle and day length, and distinguish that from Earth–Sun distance.
- Activity
- Ask students to predict June versus December, then switch the model to 0° tilt and explain what changed.
- Misconception to test
- “Earth is warmer in summer because it is closer to the Sun.”
Teacher experiment: test a no-tilt Earth directly 12–15 min · print or project
A controlled counterfactual: hold the orbit and light source fixed while changing only Earth's axial tilt. Ask students to predict an outcome before showing the answer.
- Prediction. Would northern and southern locations still have opposite summer/winter sunlight patterns if Earth were upright (0° tilt)? Write a claim and reason.
- Evidence · actual tilt. In the model, select Earth tilt: 23.5°, then compare June solstice and December solstice. Observe which hemisphere leans toward the Sun and how the day-length and sunlight-angle pattern changes.
- Evidence · zero tilt. Keep the same June and December positions. Press Compare: 0° tilt and describe the change in hemisphere contrast; the model does not measure actual temperature or weather.
- Reasoning. Which variable caused opposite seasonal patterns? Explain why Earth's small distance change cannot cause that contrast.
Device-free alternative: Put a fixed cool LED lamp (Sun) at the center of a classroom orbit and move a marked foam globe (Earth) to two opposite positions. Keep the axis tilted ~23.5° and pointing the same direction in the room at both positions. Repeat with the globe upright. Compare light at northern and southern midlatitudes. The teacher controls the lamp; never look directly at a bright light or use a hot bulb. Lamp distance, globe size and orbit are not to scale.
Model limit: With 0° tilt, the strong opposing tilt-driven seasonal effect largely disappears, but Earth's slightly elliptical real orbit still changes incoming sunlight for both hemispheres together. This does not predict constant weather.
Scientific basis: NASA Earth Facts and NASA Milankovitch Cycles. Suggested activity, not classroom-tested.
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.
Home
Solar system model
Back to the interactive 3D solar system.
AcknowledgmentsEducator and expert feedback helped improve this lesson
- A no-tilt hypothesis students can test
An astronomy editor's teaching suggestion prompted a new classroom activity: predict what changes at 0° axial tilt, compare June and December with the existing simulator or a lamp-and-globe model, and record evidence and reasoning in a printable worksheet. The 0° toggle itself predates this feedback.
Astronomy editor's pedagogical feedback
Suggestions informed specific improvements. No endorsement, formal evaluation or classroom trial is implied.
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