A sundial is a simple timekeeping tool that uses the Sun and a shadow to show how time passes during the day. In this project, you can make one with a paper plate or cardboard circle and a pencil or straw. The pencil or straw casts a shadow, and you mark where that shadow falls each hour.
This project matters because it connects everyday sunlight to Earth’s rotation and the way people measured time long before clocks.
Key Facts
- A sundial tells time by using the changing position of a shadow.
- The gnomon is the part that sticks up and casts the shadow.
- Earth rotates once every 24 hours.
- Earth turns about 360 degrees in 24 hours, so 360 ÷ 24 = 15 degrees per hour.
- A shadow is longest when the Sun is low in the sky and shortest when the Sun is highest.
- For best results, keep the sundial in the same place and facing the same direction all day.
Vocabulary
- Sundial
- A sundial is a device that uses the Sun’s shadow to show the time of day.
- Gnomon
- A gnomon is the upright or angled stick, pencil, or straw that casts the shadow on a sundial.
- Shadow
- A shadow is a dark shape made when an object blocks light.
- Rotation
- Rotation is the spinning motion of an object, such as Earth spinning once each day.
- Noon
- Noon is the time near the middle of the day when the Sun is usually highest in the sky.
Common Mistakes to Avoid
- Moving the sundial during the day is wrong because the hour marks only work if the plate stays in the same position.
- Marking the shadow only once is wrong because a sundial needs several hour marks to show how the shadow changes over time.
- Using the sundial indoors is wrong because it needs direct sunlight to make a clear shadow.
- Expecting the hour lines to be evenly spaced is wrong because a simple homemade sundial depends on location, season, and how the gnomon is placed.
Practice Questions
- 1 A student marks the shadow at 9:00 a.m., 10:00 a.m., 11:00 a.m., and 12:00 p.m. How many hour marks did the student make?
- 2 Earth turns about 15 degrees each hour. About how many degrees does Earth turn in 4 hours?
- 3 If the shadow on a sundial moves from one mark to the next as the day goes on, explain what this shows about Earth’s motion and the apparent motion of the Sun.