Earth’s tilt and the seasons
Change the date to see how Earth’s tilt affects sunlight and day length in each hemisphere.
Learning guide
What you’ll learn
Explain how Earth’s tilted axis changes day length and the angle of sunlight, producing opposite seasons in the Northern and Southern Hemispheres.
Explore: what to change
Choose Summer solstice, then Winter solstice. Compare the daylight map, sunlight angle and Earth’s position in its orbit. Then choose Spring equinox or Fall equinox.
What to look for
- Which hemisphere has longer days at Summer solstice in June? What changes at Winter solstice in December?
- Where does the yellow marker show the Sun directly overhead?
- Does Earth’s axis change direction as Earth moves around the Sun?
Why it happens
Earth’s axis stays tilted in nearly the same direction throughout the year. As Earth orbits the Sun, each hemisphere takes a turn tilting toward it. That hemisphere receives more direct sunlight and has longer days, increasing the energy it receives each day.
Questions answered
Why are the seasons opposite? When one hemisphere tilts toward the Sun, the other tilts away. The hemisphere tilted toward the Sun receives more direct sunlight and has longer days.
Does being closer to the Sun cause summer? No. Both hemispheres are essentially the same distance from the Sun on a given date, yet their seasons are opposite. Earth’s tilt explains this difference.
What happens at an equinox? The overhead Sun crosses the equator, and day and night are approximately equal in length in most places.
What is a solstice? A solstice occurs when the overhead Sun reaches its farthest point north or south of the equator. It marks the longest or shortest daylight period of the year in most places outside the tropics.
What is an equinox? An equinox occurs when the overhead Sun crosses the equator. Compare Spring equinox and Fall equinox to see the similar daylight pattern on opposite sides of Earth’s orbit.
Keep exploring
Compare daylight through the year for your town. Then use the day and night map to compare places near the equator and the poles.
Daylight for your location Day and night map Earth–Sun–Moon simulator
Teacher notes
Learning objective: Use the three views to explain why day length and sunlight angle change through the year and why the hemispheres have opposite seasons.
Suggested age range: 9–14 years. Suggested duration: 10–15 minutes. These are suggested starting points, not classroom-tested estimates.
Prerequisite knowledge: Earth rotates once a day and orbits the Sun once a year. Students should be able to locate the equator and both hemispheres.
Common misconception: Summer happens because Earth is closer to the Sun. Ask students to explain the opposite seasons visible on the same date.
Check understanding: Ask, “Why does the Northern Hemisphere have longer days in June while the Southern Hemisphere has shorter days?” A complete answer connects Earth’s tilt, daylight duration and sunlight angle.
Season names: The seasonal buttons use Northern Hemisphere names. The comparison below the controls shows the season in each hemisphere.
Source: NASA Space Place: What Causes the Seasons?
Model limitations: Sizes and distances are not to scale. The flat map distorts shapes near the poles. Earth’s axis is tilted about 23.4° from a line perpendicular to its orbital plane. The orbit diagram is viewed at 80°, and the Moon’s orbital tilt is exaggerated from about 5.1° to 18° for visibility. This model shows seasonal sunlight patterns; it does not predict temperature, weather or local climate.
Sharing a view: Copy the page URL after choosing a date. Normal is the default; a URL can also request Compact or Full details. Use Date & speed to choose an exact date or another year.
Lesson status: This is an exploration guide, not a classroom-tested lesson plan. Lesson development and drafts are separate.
Explore eclipses separately
Earth’s axial tilt causes the seasons. The Moon’s tilted orbit helps explain why eclipses do not happen every month. Change the Moon’s orbital tilt in the eclipse activity, then compare the alignment at new and full moon.
Compare Summer solstice and Winter solstice.
Earth’s axis keeps pointing the same way as Earth orbits the Sun.
1. Day & night
Watch how much of each hemisphere lies in daylight.
Change the shared date ↑The Sun is overhead at 2.1° S, 71.8° E. This is the subsolar point. Days are getting shorter in the Northern Hemisphere as Earth travels around the Sun. Earth’s axis keeps pointing in nearly the same direction.
Map limitation: Earth is a globe flattened into a rectangle, so shapes and distances — especially near the poles — are distorted. The Sun and Moon markers are enlarged so you can see them.
2. Sunlight angle
The yellow line shows where the Sun is directly overhead, called the subsolar point. Change the date to follow this point between the Tropic of Cancer and the Tropic of Capricorn.
The overhead Sun moves between the tropics. Earth’s tilt stays the same.
Change the shared date ↑The Sun–Earth centre line lands at 2.1° S, 21.4° short of the Tropic of Capricorn. The Southern Hemisphere is leaning into the light, so its days are longer than its nights.
The dashed lines mark the tropics, about 23.4° north and south of the equator. At the June solstice, the Sun is overhead at the Tropic of Cancer. At the December solstice, it is overhead at the Tropic of Capricorn.
3. Earth’s orbit
Follow the white axis as Earth orbits the Sun. It keeps pointing in nearly the same direction. Sizes and distances are not to scale.
Change the shared date ↑Earth’s axis points in nearly the same direction as Earth travels around the Sun. Compare June and December to see which hemisphere tilts toward the Sun. Explore Earth’s orbit →
What does that mean on the ground?
Compare two places equally far from the equator. Longer days give the ground more time to warm up. A higher midday Sun concentrates its light on a smaller area.
| Example latitude | Daylight | Midday Sun above horizon |
|---|---|---|
| 45° north | 11 h 44 min | 42.9° |
| 45° south | 12 h 16 min | 47.1° |
Approximate geometry for a level horizon, without atmospheric refraction. Seasons shown are astronomical seasons; local weather and tropical wet/dry seasons vary.
Try it: can distance explain opposite seasons?
Predict which place gets more daylight in June. Choose Summer solstice, then Winter solstice. Both places are on the same planet at the same distance from the Sun. Their daylight and Sun angles change in opposite directions because of Earth’s tilt.
Earth’s real orbit is slightly elliptical, with its closest approach in early January. The orbit drawing here uses a circle and enlarged bodies for clarity; it cannot measure that distance change. NASA: what causes the seasons?