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.
Understanding Build a Working Sundial
The most important step is calibration. Calibration means teaching your own sundial what each clock hour looks like in one exact place. Set the plate on a level surface and keep it from sliding.
Press the stick firmly into clay so its position does not change. At each chosen time, make a small dot at the end of the shadow, then draw a line from the base of the stick through that dot. Write the time beside the line.
Use a clock that is accurate. A few minutes of waiting can make a noticeable difference, especially near midday when the shadow may be short.
Direction matters because a sundial is built for one orientation. A compass points toward magnetic north, which is close to but not always exactly the same as geographic north. For a school project, using the same compass direction every time is usually enough.
Place the plate in that direction before recording marks and before testing it later. If the plate is turned, even a little, every hour line shifts.
A tilted plate can cause errors too. A book or flat board under the plate can help create a steadier surface.
The shadow does not move in equal-looking distances across the plate. It may sweep quickly across one part of the plate and spread out differently in another part. This happens because the Sun follows a curved path across the sky, while the plate is flat.
The length of the shadow changes as well. Near noon, the Sun is higher, so the shadow is often shorter.
In morning and afternoon, the Sun is lower, so the shadow becomes longer. Recording both the direction and length of the shadow turns the project into a useful observation of changing angles.
Your sundial may not match the time on a phone perfectly. Clock time is arranged in time zones, so everyone in a large area follows one standard time. Daylight saving time can shift clocks by one hour in some places.
The Sun is not always highest in the sky at twelve o'clock on a clock either. Your location east or west within a time zone affects this. Seasons matter too.
The Sun takes a higher path in summer and a lower path in winter, changing the shadow pattern. These differences are not mistakes. They show that measuring time from the sky is more complex than reading a digital clock.
Test the finished sundial on another sunny day. Set it in the same place and direction, then compare the shadow with your hour lines. Write down whether it is early, late, or close.
Clouds, wind, a loose stick, or a moved plate can affect the result. Never look directly at the Sun while working.
Watch the shadow on the plate instead. A careful record of small errors is valuable because scientists use repeated tests to decide whether a model is reliable.
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.