Earth orbits the Sun with its axis held at a 23.4 degree tilt. Choose an equinox or solstice, or use the time-of-year slider. The information panel reports the northern and southern seasons and the subsolar latitude.
Guide · kids, parents & teachers
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Why do we have seasons?
Seasons happen because Earth is tilted . Its axis leans about 23.4° and keeps pointing the same way in space all year. So for part of the year the Northern Hemisphere leans toward the Sun, and for the other part the Southern Hemisphere does.
Is Earth closer to the Sun in summer?
No, and this is the most common mix-up about seasons. Earth is actually closest to the Sun in early January, during winter in the Northern Hemisphere. Its distance changes by only about 3% over the year (roughly 147 to 152 million km). That is far too little to cause seasons. And if distance were the reason, the whole planet would have summer at the same time. It doesn’t.
How does the tilt make summer warmer?
When your half of Earth leans toward the Sun, two things happen:
The Sun climbs higher in the sky. Its light hits the ground more directly, so each patch of ground gets more energy.Days are longer. There are more hours of warming and fewer hours of cooling at night.
When your half leans away, the Sun stays low and the days are short. That is winter. Try it with a flashlight: shine it straight down on paper, then tilt it. The same light spreads into a bigger, dimmer patch, just like winter sunshine.
What are solstices and equinoxes?
June solstice (about June 20–21): the Northern Hemisphere leans most toward the Sun. It is the longest day in the north and the shortest in the south.December solstice (about December 21–22): the reverse. Summer begins in the south and winter in the north.March and September equinoxes (about March 20 and September 22–23): neither hemisphere leans toward the Sun, and day and night are close to 12 hours each almost everywhere.
The exact dates shift by a day or so between years and time zones.
Why are the seasons opposite in Australia?
The same tilt that points the north toward the Sun points the south away from it. When it is summer in Canada or the UK, it is winter in Australia, Argentina and South Africa. In the model, watch the Northern half and Southern half boxes swap as Earth travels around the Sun.
How to use this model
Pick a solstice or equinox, or drag the Time of year slider. Turn on Sunlight to see which half of Earth gets the most direct light, and Axis to see that the tilt never changes direction. The orbit is drawn as a circle, and sizes and distances are squeezed to fit on screen.
For teachers
Ages 8–14 (grades 3–8)
Time 15–25 minutes
Standards NGSS MS-ESS1-1, 1-ESS1-2
Learning goals
Explain that seasons are caused by Earth’s tilt, not its distance from the Sun.
Describe how the angle of sunlight and the length of the day change through the year.
Predict the season in the opposite hemisphere.
Try this in class
Before opening the model, ask “Why is summer hot?” and write down the answers. Many students will say Earth is closer to the Sun.
Project the page. Choose June solstice and ask which half of Earth leans toward the Sun. Then choose December solstice .
Turn on Axis and play the year. Does the tilt change direction as Earth travels? (No, it keeps pointing the same way.)
Do the flashlight test on squared paper: count how many squares are lit when the light shines straight down, then when it is tilted.
Go back to the opening answers and have students correct them in their own words.
Discussion questions
If Earth had no tilt at all, would we still have seasons?
It is winter where you live. What season is it for a pen pal in Australia, and why?
Earth is closest to the Sun in January. Why isn’t January the hottest month in the north?
Uranus is tipped right over on its side. What might its seasons be like?
Sources
NASA Seasons
USNO Seasons and orbit
USNO Season dates
Reviewed Sep 27, 2026