Children are able to understand all kinds of complicated information if it is presented to them in a way they can relate to. If you present information about sundials in a fun way, and they have previous knowledge about the components of the earth needed to understand sundials, the lessons you create will be enjoyable for everyone. Students in grades 2 through 6 should be able to understand that sundials are used to measure time and how the Earth rotates, causing the sun to cast shadows in different ways throughout the day.
Tell students that sundials work based on the rotation of Earth. Students must first understand that the sun stays in one place and that the planet spins around the sun. Next, they must comprehend that the sun appears to move across the sky because Earth is spinning on its axis. If necessary, teach these concepts using a group of students acting as the sun and all of the planets and have them rotate around the sun while spinning.
Explain that the Earth makes a rotation around its axis every 24 hours and that this makes day and night. Students must understand that part of the planet is facing the sun, making it daylight, while the other part of the world faces away from the sun, making it night. If necessary, use a globe and a flashlight and shine the flashlight on the globe while spinning it to demonstrate that the light only hits part of the globe, while the other part is dark.
Tell students that the Earth is tilted on its axis so that the North Pole is pointed at the sun for six months and away from the sun for six months. This is important for understanding that the shadows cast by the sun change day by day throughout the year. If necessary, use a globe tilted on an angle and shine the flashlight on it to demonstrate, but be sure to move the globe around the "sun" (flashlight) to show that for half of the rotation, the North Pole is light and for the other half, it is dark.
Explain that because the Earth is round, the ground at the base of a stick would not cast a shadow at the same angle as at the equator. Help students understand that the curve of the Earth causes the shadows to move gradually during the day. Explain this using observation where students put a long stick in the ground, then observe it over the course of the day to see that the shadow moves.
Tell students that because humans understood the information about the Earth and its rotation, they knew that the best way to angle the sundial was to put it at an angle and aim it north. The angle compensates for the tilt of the Earth, making the hours on the sundial consistent all day and all year. The angle of the stick, called a gnomon, varies depending on the latitude you are in. Explain this using the same long stick, but put it at an angle and aim the stick north. Have students compare and contrast the difference between the first stick that was straight up and the second stick that was angled and facing north.
Explain that as you move to different lines of longitude across the Earth, the sundial will read a different time. Students must understand the concept of time zones, so for each line of longitude, the sundial will read a different time. Spin the globe slowly, showing that a little bit more of the Earth becomes exposed to the sunlight.
Have students make their own sundial to truly understand how they work, then use them outside to record observations.
Children will be tempted to look at the sun, so warn them before they go outside of the dangers of this behaviour.