How to make a Sun Dial

Before there were digital clocks, circular clocks, or grandfather clocks, people told time by using the sun. While knowing where the sun is in the sky can give an approximate time, a sun dial can be used to tell the exact time if the measurements are done carefully. Here is a simple way to make a sun dial that you can use to tell time in your yard. It will only work on sunny days during the daytime, of course. This article does not give the directions for a totally scientific sun dial- it is meant to be an introduction to the concept. If you pay attention to your sun dial you will discover that the length of the shadow changes throughout the day and also throughout the year. The links at the end of this article will help you to understand why that happens. You can also use the links to help you find the solar noon for where you live so that you can use the sun's shadows more accurately. Remember that if it is daylight savings time, the sun's shadows will not match your clocks or the official time in your area.

Things You'll Need

• 3-foot-long dowel with a diameter of 1 inch
• 12 10-inch lengths of 1/2-inch-diameter dowel
• Watch
• Hammer
• Permanent marker

Instructions

1. Pound the large dowel into the center of an open area outside where nothing blocks the sun from shining on the stick. As the sun moves across the sky from the eastern horizon at dawn to the western horizon at sunset, the stick's shadow will move in a circular motion. It may take several sunny days for you to mark the ground so that just by looking at where the shadow falls, you will know what time it is.

2. Be outside on the hour to mark where the shadow falls. Pound a small dowel into the ground about three feet away from the large stick so that the small dowel touches the shadow formed by the large stick. Use the permanent marker to put the date and time on the small stick.

3. Return to the sundial every hour. The shadow from the large stick in the center will be in a different place every time you go outside. On the hour, pound in a new small dowel and mark it with the date and the time. Every day the shadow from the center stick will fall on the small sticks in the same order, hour by hour, in a pattern that you can learn to recognize and use to tell time.

4. Adjust how you interpret the time whenever the government changes the clocks if you live where there is daylight savings time during a portion of the year.

5. Invite your friends to visit your yard to see how a real sundial works. You can even make a smaller, movable sundial with nails and a block of wood. Just be sure to put the largest nail in the middle and to arrange twelve smaller nails so that the lines formed from the center to the outside create the same size angles as the stick sundial in your yard. Make the horizontal line of the angle goes through the center stick like it does on a protractor.

Tips & Warnings

• Making a sundial is a wonderful science project for elementary school classes.

Resources

• This is a lesson plan that shows how to adjust for the different lengths of shadows at various times throughout the year. It also links you to where you can calculate solar noon for your location.
• This explains how shadows change throughout the year. It also tells where to go in the world to be where you won't cast a shadow on certain days of the year.
• If you want to make a totally exact sundial, then use this website to calculate the solar noon for your location and also follow the instructions for positioning a sun dial.