Build your own ancient time-telling device using the sun! You will learn how the Earth's rotation creates moving shadows to track the hours of the day.

Tools

• sidewalk chalk
• compass (or smartphone compass app)
• marker (1)

Materials

• straight stick or drinking straw (12 inches, 1)
• paper plate (12-inch, 1)
• small pebbles or rocks (10-12)

Safety

• Adult supervision required when poking holes in plates.
• NEVER look directly at the sun, as it can damage your eyes.
• Be careful when using sticks or straws to avoid poking yourself or others.

Steps

1. Find a flat, sunny spot outdoors where the sun shines all day without being blocked by trees or buildings.
2. If using a paper plate, find the exact center and have an adult help you poke a small hole through it.
3. Insert your stick or straw (the gnomon) through the hole in the plate or push it firmly into the ground.
4. Determine which way is North or South. If you are in the Northern Hemisphere, tilt the gnomon slightly toward the North. If you are in the Southern Hemisphere, tilt it toward the South.
5. Starting at 7:00 AM, go outside and look at where the shadow of the gnomon falls on the plate or ground.
6. Mark the exact edge of the shadow using a pebble, a piece of chalk, or a marker. Label this mark '7'.
7. Set an alarm for every hour. Each time the alarm goes off, return to your sundial and mark the new position of the shadow with a number (8, 9, 10, and so on) until the sun sets.
8. Once all marks are made, you can use your marker or chalk to draw straight lines from the gnomon to each mark, creating a wheel of time.
9. Test your sundial the next day! Look at where the shadow falls and see which number it aligns with to tell the time.