Rays on a round Earth

The idea

On the spherical Earth the Sun's rays strike latitudes at different angles: radiation is concentrated on a smaller area at the equator and spread over a larger area near the poles, so equatorial regions are warmer.

Two beams of sunlight

Two equal beams of sunlight fall on a round ball. One beam hits the middle of the ball, the other hits near the top.

Does each beam light up the same size of patch?

• No, the top beam spreads wider
• Yes, the same size
• The top beam gives a smaller patch

Two beams, two patches

Press Next step.

Shape makes the difference

Because the Earth is a sphere, the same Sun sends its rays to different places at different angles. The heating is uneven, and this creates temperature differences between the equator and the poles.

On the spherical Earth the Sun's rays strike different latitudes at different angles. Radiation is concentrated on a smaller area at the equator and spread over a larger area near the poles, so equatorial regions are warmer.

Notes

The Earth is round, so rays strike latitudes at different angles: concentrated at the equator, spread out near the poles, so the equator is warmer.

Check yourself

Where is the Sun's radiation concentrated over a smaller area?

Why do the Sun's rays strike different latitudes at different angles?

Why do equatorial regions stay relatively warm while polar regions are much colder?

What does the uneven heating of the Earth's surface across the globe drive?

• Near the poles. Near the poles the radiation is spread over a larger area.
• Near the equator — correct. Yes!
• Equally everywhere. The rays strike different latitudes at different angles, so the area is not the same.
• Clouds block the rays at some places. The chapter explains the different angles by the spherical shape of the Earth.
• The Sun moves closer to some places. The chapter explains it by the Earth's shape, not by the Sun moving closer to places.
• The Earth is spherical — correct. Yes!
• Radiation is concentrated over a smaller area at the equator and spread over a larger area at the poles — correct. Yes!
• Polar regions receive no radiation from the Sun. Polar regions do receive radiation, but it is spread over a larger area.
• Equatorial regions are nearer to the Sun. The chapter explains it by the angle of the rays and the area they cover, not by distance.
• The Earth's spherical shape. The spherical shape is one of the causes of the uneven heating, not something it drives.
• Global winds and ocean currents — correct. Yes!
• The tilt of the Earth's axis. The tilt, with the shape, gives seasons and varying daytime. It is not driven by the uneven heating.