Click a marked position to place Earth there.

What this drawing simplifies

The path is really a circle. It looks like an oval because we are looking at a circle from an angle, the way a plate does from across the table.
Not to scale. The Sun is about 109 times wider than Earth, and much farther away than this can show.
Do not measure the tilt. It reads steeper than 23.5 degrees, for the same reason the path looks oval.
N and S mark the poles, where the axis meets Earth's surface.
The dates shift a little each year. June solstice: June 20 or 21. September equinox: Sept 22 or 23. December solstice: Dec 21 or 22. March equinox: Mar 19 or 20.

Positions placed · 0 of 4

Step 1 of 4

Build the year

Earth revolves around the Sun once a year. Four positions in that orbit are marked for you: two solstices and two equinoxes.

Try this

Click each of the four marked positions to place Earth there. Fill all four before you move on.

Same sunlight. How high the Sun is decides how far that energy spreads.

How high is the Sun at noon in Texas?

At the June solstice, Texas has more of its day in sunlight. Sydney has less.

How to read this picture

Each coloured circle is a line of latitude, the path a place follows as Earth rotates once a day.
Bright means that part of the circle is in sunlight. Dim means it is in the dark.
The equator is split exactly in half, and it stays that way all year.

Step 2 of 4

Why tilting toward the Sun makes it warm

Both settings send the exact same bundle of sunlight at the ground. The only thing that changes is how high the Sun is, which decides whether that light comes straight down or slants in.

Try this

Click High (June solstice), then click Low (December solstice), and watch the orange bracket on the ground change. You have to look at both before you can move on.

One Earth, one moment, two opposite seasons.

How to read this picture

A hemisphere is one half of Earth, split at the equator.
Each season word sits at the pole of the hemisphere it belongs to. Orange for the north, blue for the south.
The dashed circles are the other three positions in the orbit.

Move Earth around its orbit · 1 of 4 seen

Step 3 of 4

Two hemispheres, two seasons, same moment

Northern Hemisphere · Texas

Summer

Southern Hemisphere · Sydney

Winter

Try this

Step through all four positions and watch both boxes at once. They never match.

The model stays here so you can check your thinking.

Step 4 of 4

Challenge

Try this

Seven questions. Answer each one to unlock the next, and use the model on the left whenever you need to check something. You can go back with the numbered buttons.