Making a Sun Clock

How did people tell time before our analog and digital clocks were invented?

They used the SUN! 

In this Science and Math Activity, we will make a Sun Clock.

Materials

• cardboard or heavy paper
• pencil and marker
• protractor
• clay
• watch 
• compass

Directions

• Place the protractor on the cardboard.
• Draw around the outside of the protractor.
• Mark the following angles: 0 degrees, 30 degrees, 60 degrees, 90 degrees, 120 degrees, 150 degrees, 180 degrees.

• Turn the protractor around and again draw the outside of the circle (to complete the circle). 
• Then mark the same angles.

• Write the clock numbers (1-12) on the circle as they appear on a clock.

• Place a small wad of clay in the middle of the clock and place the pencil in the clay so that the pencil stands straight up.

• On a sunny day, take the clock outside and use a compass to locate NORTH.
• Place the clock on the ground in the Sun. Have the number 12 facing North.
• Observe the shadow made by the pencil.
• "Does the shadow made by the pencil on the clock tell you the time?"

• Check the time with your watch.
• "Compare the time on the shadow clock with the time on your watch.
• Does your shadow clock tell the right time? {No}"

Explanation:

"This is because the Sun does not move in a circle around the sky. Instead, it moves in an arc from east to west across the southern sky.

Shadows fall within the arc formed between East-North-West. Shadows are shortest at noon and longest at sunrise and sunset."



diagram by Janice VanCleave

• Have students continue to observe the movement of the shadow over time. 



Photo Diagram by Janice VanCleave

Sun Clock / Sundial

Further Explanation

During the day, it will appear that the position of the Sun is changing but really it is the Earth moving as it rotates on its axis.

(The time will be off by one hour during daylight savings time.)


DEAR Reader,
This post has been edited. My original explanation had some errors. I was contacted by the incredible Janice VanCleave. She kindly explained how to fix my errors and included some wonderful diagrams that I could share with you. I apologize for my previous errors and thank Janice for reading my post, contacting me, and helping me correct the information.

Janice is awesome! She is the author of 50 best selling science experiment books for kids! :) You can visit Janice's blog at http://scienceprojectideasforkids.com/.  I just visited and signed up for her newsletter! :)

Enjoy your new clock!