A shadow is a clue that changes. To use it for time, a person needs more than a dark shape: the marks must have an agreed meaning.

The Met museum has an Egyptian shadow-clock fragment dated between 305 and 30 BCE. BCE means before the Common Era, before year 1 in this dating system. Lines were cut into its sloping face. A missing upright part would have cast the shadow.

This object used shadow length to mark time. It is one dated example, not proof that all old timekeepers had the same shape. A device that depends on sunlight also has a limit when the sky cannot supply a clear shadow.

Writing a clock time beside your shadow mark connects an observation with a familiar scale. Without that comparison, the mark tells you a position but not automatically an hour. Historical timekeeping involved choices about marks as well as noticing changes.

People also used water. In ancient Egypt, water vessels could lose water through a small hole. Greek water clocks from about 325 BCE also used controlled flow. BCE means before the Common Era, before year 1 in this dating system. Levels were compared with marks.

Some clocks slowly emptied; others slowly filled. Both needed to connect a level with passing time. They could work without a visible shadow, including at night.

Your cup is a simple model. An interval is the time between two moments. Marking the level after equal intervals lets you examine whether the marks stay regular.

Do not assume equally spaced marks mean equal time. Flow can change as a cup empties, and a homemade hole can behave unevenly. Your model may leak too quickly or stop. Record that honestly. It measures a possible interval after a chosen start, not automatically the time of day.

together · About 8 minutes; estimate

You need

• Paper cup and bowl
• Water and pencil
• Household clock or agreed slow count
• Paper

Try it

1. Ask your adult to prepare a draining hole and hold the cup upright above the bowl.
2. Add a little water; look down into the cup and pencil a short starting mark on its inside wall.
3. After one minute on a clock, mark the inside level again.
4. Wait another minute and make a third inside mark.
5. Compare the level gaps and repeat if useful.
6. If using agreed counts instead, label both intervals approximate.

together · About 5 minutes at two visits; estimate

You need

• Stable upright household object
• Paper and pencil
• Household clock for outdoor version; lamp for indoor alternative

Try it

1. Place the object on paper in a safe sunny spot; look only at its shadow.
2. Trace the shadow tip and write the clock time.
3. Leave the object and paper in the same position.
4. Come back later and mark the tip and time again.
5. Compare the marks and explain what gave them time labels.