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Subjects
A paper plate sundial with the shadow of its stick falling across the marks The Sun is on the left with rays coming off it and a dashed beam crossing to the right. There a round plate is marked with ticks all the way round its rim. A tall pointed stick stands at the centre of the plate, sticking up past the top of it, and casts a dark wedge of shadow down towards one of the ticks.

Make a Fun and Simple Sundial

About 6 minutes

A sundial tells time using nothing but a shadow. As the sun moves across the sky, the shadow it casts moves too, and marking where it falls each hour turns a paper plate into a clock.

What You'll Need

Before you go outside

Steps

  1. Find a sunny spot outside.
  2. Place your paper plate flat on the ground.
  3. Use the ruler to draw a line from the center of the plate to the edge. This is your 12 o'clock line.
  4. Place the clay or playdough in the center of the plate.
  5. Stick the pencil straight up in the clay. This is your gnomon — the part that casts the shadow.
  6. Check your watch. Mark where the pencil's shadow falls on the plate with a small line, and write the time next to it.
  7. Wait an hour. Mark where the shadow falls now and write the new time.
  8. Keep marking the shadow's position every hour.
  9. The marks you have made are now your sundial — line the shadow up with one of them at any time to read the hour.

Why This Works

The sun's position in the sky changes throughout the day. The pencil casts a shadow that moves as the sun moves. By marking the shadow's position at different times, you create a way to tell time using the sun.

The part that makes it work is simple enough to say in one line: a shadow always points away from the light. So when the sun is low on one side in the morning, the shadow stretches out on the other side. Move the sun and watch the shadow answer.

A sundial seen from above, with the sun and the shadow on opposite sides A round paper plate lies flat with a pencil standing upright in the middle, seen from directly above so the pencil is a small circle. The sun sits outside the plate on one side, and the pencil's long shadow stretches right across the plate on the exactly opposite side. When the sun moves across the sky the shadow swings the other way, because a shadow always points away from the light. the shadow points away from the sun

Drag the handle to move the sun across the sky, and watch what the pencil's shadow does.

This is a simple picture of the idea rather than an exact clock — your real plate is the accurate one, because you mark it from your own sky.

Your sundial's shadow has moved since you last looked. What actually moved to make that happen?

What to try next

Make your sundial again a few months later, in the same spot, and lay the two plates side by side. The hour marks will not land in quite the same places, because the sun does not take exactly the same path across the sky in summer as it does in winter.