A sundial is a simple clock that uses the Sun and a shadow to show time. For this project, you can build one with a paper plate, a pencil or stick, clay, a compass, and a marker. Sundials matter because they show how people measured time long before batteries and phones.
They also help you see that science can be built and tested with everyday materials.
The upright pencil or stick is called a gnomon, and its shadow moves as Earth rotates. Earth turns once every 24 hours, so the Sun seems to move across the sky from east to west during the day. On a sunny day, you can mark the shadow each hour from 8am to 5pm to make hour lines on the plate.
The sundial works best when it stays flat, points the same direction, and is used in the same location where it was marked.
Key Facts
- A sundial uses the shadow of a gnomon to show the time.
- Earth rotates once every 24 hours.
- 360 degrees / 24 hours = 15 degrees per hour.
- The Sun appears to move from east to west, so shadows change direction during the day.
- A compass helps you line up the sundial in the same direction each time.
- For this project, mark shadow positions each hour from 8am to 5pm.
Vocabulary
- Sundial
- A sundial is a tool that tells time by using the shadow made by sunlight.
- Gnomon
- A gnomon is the upright stick or pencil on a sundial that casts the shadow.
- Shadow
- A shadow is a dark shape made when an object blocks light.
- Compass
- A compass is a tool that points north and helps you line up directions.
- Rotation
- Rotation is the spinning motion of an object, such as Earth turning once each day.
Common Mistakes to Avoid
- Moving the plate after marking it is wrong because the hour lines only work if the sundial keeps the same direction.
- Tilting the pencil or stick by accident is wrong because a leaning gnomon changes the shadow path and can make the time marks inaccurate.
- Marking times on a cloudy day is wrong because weak or blurry shadows are hard to place correctly.
- Forgetting to label each hour is wrong because the marks will not help you read the time later.
Practice Questions
- 1 A class marks a sundial every hour from 8am through 5pm. How many hour marks will they make if they include both 8am and 5pm?
- 2 Earth turns 360 degrees in 24 hours. How many degrees does Earth turn in 3 hours?
- 3 A sundial worked well on the playground, but then a student turned the plate to face a new direction. Explain why the sundial might show the wrong time now.