Look at your first shadow drawing. A shadow forms when an object blocks light. Light usually travels in straight lines, so the blocked area makes a dark shape.

When the Sun is low, its light reaches you from a lower angle. Your shadow stretches farther across the ground. When the Sun is higher, the shadow is shorter.

The Sun seems to travel across the sky during a day. Earth is turning, and that turning changes our view of the Sun. As the apparent Sun position changes, your shadow changes too.

Your own traced shadows can show this without needing a picture in a book. Compare the time, direction, and length before deciding what pattern you see.

A claim becomes stronger when you can point to evidence. Your traced shadows are evidence you made yourself.

Trace a shadow, write the time, and trace it again later in a different color. A drawing can show where the shadow began and where it moved.

One trace cannot show a pattern. Two or three traces can help you compare. Did the shadow get longer or shorter? Did its tip move?

Clouds, uneven ground, and a changing place can make a comparison less clear. Write what happened instead of forcing a neat answer. That is what careful observers do.

A sundial is a clock made from a shadow. Its upright stick is called a gnomon, a word for the part that casts the shadow.

Place the gnomon in one spot. Each hour, mark the tip of its shadow and write the time. Your marks become a local shadow map.

Later, a shadow tip near one mark can help you guess the time. The shortest shadow marks solar noon, when the Sun is highest for that day in your local sky.

A sundial is not the same everywhere. Place, season, and the way the gnomon stands all matter. That is why your own marks are more useful than copying someone else’s.

Long ago, Eratosthenes heard about a puzzle in Syene, a city in Egypt. At a particular time of year, sunlight could shine straight down a deep well there.

In Alexandria, another city, a vertical stick made a shadow at that same time. Eratosthenes compared the two places and used the difference to estimate the size of Earth.

His idea began with two sticks, two cities, and one moment. If Earth were a flat surface and sunlight came from very far away, matching sticks would make matching shadows at the same moment. They did not.

Eratosthenes’ calculation used measurements we will not do here. Your job is to notice the puzzle and compare a flat surface with a round model indoors.