Horrible Science: The sundial watch

It might look like the Sun moves across the sky, rising in the morning and setting in the evening, but really it’s the Earth that’s moving!

The Earth spins around on its axis, an imaginary line that goes through the North and South poles, once every 24 hours. As it turns, different parts of the planet face the Sun making it seem like the Sun is moving from east to west.

When the part of Earth you are on faces the Sun it’s daytime, and when it turns away it’s nighttime. So, the Sun isn’t moving across the sky, we are!

A sundial, also called a shadow clock, is one of the oldest ways to tell the time using the Sun! It works by using the Sun’s position in the sky to make a shadow move.

A sundial has a stick, called a gnomon, in the middle. When sunlight hits the gnomon, it casts a shadow on a flat plate with numbers or marks. As the Earth turns, the position of the Sun in the sky changes and the shadow moves too.

The shadow points to different numbers on the sundial during the day,as time passes, showing what time it is. We call it noon when the shadow is at its shortest and the Sun is at its highest point. Sundials only work when the Sun is shining and the Earth is facing the Sun. So good luck telling the time with a sundial on a cloudy day!

Horrible Science fact

The Sun is actually a star and it’s the closest star to Earth! It looks much bigger and brighter than all the other stars because it’s so much closer to us. The Sun is a giant ball of hot gas and it’s so big that over one million Earths could fit inside it!

Find out more about the Sun.

Play our Stinky Space game and learn more about the Sun and our Solar System.