An axis is an imaginary line an object turns around. You can imagine one running through your ball from one end to the other. Earth’s axis is tilted rather than standing straight compared with its path around the Sun.

When one pole leans toward the Sun, sunlight reaches around that polar end. Some places near it can remain in sunlight while Earth makes a full turn. The Sun stays above the horizon, the apparent boundary between sky and land or sea.

This is called the midnight Sun. Midnight is a clock time, but darkness is not guaranteed at that time in every place. Your near-pole mark may stay lit while a middle mark enters shadow. Observe those different paths before deciding that one room demonstration describes every place on Earth.

Long daylight has a partner: long darkness. When a polar end leans away from the Sun, some places near it do not receive direct sunlight during a full turn. This is called polar night.

The two ends of Earth do not lean toward the Sun together. While one polar region has long daylight, the opposite region is oriented away. Their daylight patterns differ.

How long these conditions last depends on where a place is and the time of year. Do not copy one city’s pattern onto every polar place. We are investigating a spatial puzzle, not calculating a calendar of seasons. Moving the marked ball lets you compare orientations indoors. Nobody needs to look at the Sun to discover why a rotating mark might avoid the model’s shadow.

together · About 10 minutes; untested estimate.

You need

• Ball
• Tape and paper marks
• Flashlight
• Paper and pencil

Try it

1. Mark two opposite poles and draw a line around the ball’s middle.
2. Place one dot near a pole and another on the middle line.
3. Use a beam wide enough to cover the whole ball. Tilt the marked pole toward it.
4. Turn the ball around its pole-to-pole line, keeping that line tilted the same way.
5. Compare the two dots over a full turn. Then repeat with that pole tilted away.