Omar shines a flashlight straight down at a sheet of paper. The light makes a small, bright patch.

Omar's flashlight, held straight above the paper and then tilted.

Now he tilts the flashlight, so the light lands at a slant. The same light makes a long, dim patch.

The same light: a small, bright patch when it lands straight on, and a long, dim patch when it lands at a slant.

The same light is spread over more paper, so each bit of paper gets less light.

Sunlight does the same on Earth. Earth is a ball, so near the equator the sunlight lands straight on the ground.

Two beams of sunlight the same width: at the equator the beam lands on a small patch of ground; near the North Pole it lands on a big patch.

Near the poles, the sunlight lands at a slant.

The same sunlight is spread over more ground, so each patch of ground gets less.