Make a Sundial in the Garden and Let the Sun Tell the Time

A sundial is a clock with no cogs, no battery, and not a single moving part. Yet it tells the time — as long as the sun is shining. How can a stick in the ground know what time it is? The answer is hanging over your head right now, and it is moving slowly while you read. Making a sundial with children is one of the simplest ways to make that movement visible. But here is the strange part: your sundial will never run wrong — and yet it will almost never quite agree with the clock on the kitchen wall.

In short:

• The sun appears to arc across the sky, from the east in the morning to the west in the evening.
• A stick in the middle of the sundial casts a shadow that travels round in step with the sun.
• The shadow is long in the morning and evening, and shortest in the middle of the day.
• Mark the shadow every full hour and you have built a clock the sun itself drives.

What is a sundial, and how does it work?

A sundial is a tool that measures time using the shadow the sun makes. In the middle of the sundial stands an edge or a stick — it is called a gnomon — and it is the shadow from this that tells the time. As the sun moves across the sky, the shadow slides slowly round the surface, like one single long, silent hand.

Picture a flagpole in the schoolyard on a sunny day. Early in the morning its shadow lies long and slender across the ground. Through the morning it shrinks and turns. Right in the middle of the day, when the sun is at its highest, the shadow is at its very shortest. Then it grows out again towards the other side as afternoon turns to evening. A sundial captures exactly this journey and puts numbers to it.

And here comes the part that surprises most children: it is not the sun that moves — it is the Earth that spins. We stand on a globe that turns once a day, and from the ground it looks as though the sun is sailing over us. So a sundial does not really measure the sun at all. It measures how far the Earth has turned since this morning. Anyone who wants to understand how everyday things like this connect to big ideas can read more about what STEAM learning is really about.

Why is this worth a child knowing?

"What time is it?" children ask long before they can read a clock face. A sundial turns that question on its head: instead of learning the time by heart, the child gets to see where it comes from. Norway's LK20 curriculum asks pupils in the early and middle years to explore how day and night are linked to the Earth's rotation. A sundial turns that connection into something you can touch, not just something in a book.

The lovely thing is that the child builds something real with their own hands, and at the same time discovers one of the biggest ideas in science almost for free. The travelling shadow is proof that we stand on a planet in motion. When a child grasps that, the sky feels a little less distant and a little more like something they are part of. And because a sundial demands patience — you have to wait for the next full hour to mark the shadow — it also practises something hard: letting time pass slowly and watching what happens.

Try it at home: build your own sundial

Suitable for: 6–12 years

You will need:

• ✅ A straight stick or a pencil (the gnomon)
• ✅ A flat spot in the sun — grass, sand, or a paper plate on the ground
• ✅ 8–10 small stones or twigs to mark with
• ✅ A marker or chalk to write the times
• ✅ A sunny day and a little patience

How to do it:

1. Stand the stick upright in the ground in a spot that gets sun all day.
2. Wait for the next full hour, and lay a stone where the tip of the shadow falls.
3. Write the time beside the stone.
4. Repeat every full hour through the day — one stone and one time each time.
5. Watch how the stones form a fan around the stick by the end of the day.
6. The next sunny day, you can read the time by seeing which stone the shadow points to.

⚠️ An adult helps set the stick firmly so it does not topple over during the day.

The sundial also works beautifully alongside a quite different kind of sun magic: make sun prints where the sun bleaches the paper. What happens if you try the sundial on a day with light clouds — can you still read the time between them?

Questions to wonder about

• If the shadow tells the time, what kind of clock did people have before they invented the sundial?
• Why are summer days in Norway so much longer than winter days — and what does that do to the sundial?
• Could there be a clock that works at night, with no sun — and what would it measure instead?

The next time you walk past a lamppost or a flagpole on a sunny day, stop for a moment and look at the shadow. It does not lie still — it travels, slowly and surely, because the whole planet beneath your feet keeps on spinning. A sundial is simply a way to make that journey visible, and to let a child feel that time is bound up with the sky. Every child is made of good atoms. At Good Atoms we help them see the big ideas hiding in an ordinary shadow. See how Good Atoms builds on this topic.