Build a Shadow Clock (Sundial)
Introduction:
Before mechanical clocks, ancient civilizations used the sun’s movement across the sky to measure time. Galileo often timed his observations using natural light and shadows, particularly before more advanced timekeeping devices were invented. This hands-on activity introduces children to how sundials work and how the position of the sun creates shifting shadows throughout the day. By building a simple sundial, children begin to understand Earth’s rotation and how people in Galileo’s time relied on astronomy to track time. They will also gain a deeper appreciation for how scientific instruments evolved from simple observations to precision tools.
What You Will Need:
A paper plate or sturdy piece of cardboard
A sharpened pencil, stick, or straw
Ruler
Compass or compass app
Clock or watch
Markers or pens
Notebook and pencil for observations
Step-by-Step Instructions:
Use a compass to find true north and place the paper plate on a flat surface outside, oriented correctly.
Poke the pencil or stick through the center of the plate so that it stands upright. This will act as your gnomon (the part of a sundial that casts the shadow).
Check the time and mark the tip of the shadow on the edge of the plate. Label it with the correct hour.
Come back every hour throughout the day and mark where the tip of the shadow falls. Label each new mark with the corresponding time.
At the end of the day, connect your marks with a smooth curve to see the sun’s path.
The next day, use your sundial to tell the time and compare it with a real clock.
What to Look For:
How does the position of the shadow change throughout the day?
Are the intervals between marks evenly spaced?
What happens to the shadow’s length as the sun rises and sets?
Fun Fact:
The word “gnomon” comes from the Greek word for “one who knows.” It is the part of the sundial that casts the shadow, and its angle is often matched to the latitude of the observer’s location.
Safety Tip:
Remind children never to look directly at the sun while observing the sundial. Always look at the shadow on the ground or plate.
Journaling Prompt:
Sketch your sundial and label at least three different times marked during the day. Write a short paragraph about how people in Galileo’s time might have used sundials to plan their daily activities.
