Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

April 17, 2014

“Mom! Dad! What time is it?”

Time to get a watch, of course!

What parent hasn’t heard the “What time is it?” question and its cousin, “How much longer?” Kids can answer their own question by making a paper plate sundial.

Our day has 24 hours–the amount of time it takes for the earth to rotate once around its axis.

The game “Dizzy Bat” used to be a field day and camp color wars highlight. Grab a bat and hold it upright. Have your child lean to place her forehead on the bat (or Sun) and spin her body around it to illustrate the Earth’s rotation. How quickly can she spin around? How many times can she spin around before she gets dizzy and falls down?

Due to the Earth’s rotation, the Sun appears to move across our sky. Ancient people used the sun’s position in the sky to tell time. It was most likely the Egyptians who realized that it is possible to measure time by the shadows created from the position of the sun. The sundial, the simplest and earliest clock used this idea to mark the hours.

Make a Simple Sundial

The most basic type of sundial is made from a horizontal circle and a vertical stick, called the gnomon.

1. Poke a hole in the center of a paper plate with a pencil.

2. Push a straw through the center of a (convex side up) paper plate.

3. Use a little glue or tape to hold the straw in place.

4. Take it outside at noon and then mark the hours.

Were the marks at regular intervals? Older kids might notice that a circle has 360 degrees and the day has 24 hours so if the hours are marked at regular intervals, they would be at every 15 degrees.

Will the sundial work tomorrow? How about three months from now?

More Accurate Sundials

You can improve the accuracy of your sundial by angling your gnomon so it is at the same angle as your latitude and pointing your gnomon to the south. The easiest way to do this is to cut out a card stock triangle with the correct angle.

Older kids may notice that you need one angle at your latitude, one 90 degree angle, and a third angle that makes up the difference between the first two angles and the total 180 degrees needed for a triangle.

Because the sun’s path through the sky appears lower during winter and higher in the sprint, a perpendicular gnomon will have shifting shadows. Take a look at this interactive animation that shows why angling your gnomon creates a more accurate sundial.

You could also try to make this neat equatorial sundial.

Measuring Time

My daughter was pondering how we can “measure” the “length” of time when we cannot see or touch the hours. Sundials are one way we can “see” time so that we can measure it.

Sand hourglasses, water clocks, and melting candles are other ways people measured time before we had mechanical clocks.

Now that you have a sundial, try using it to tell the time. Does it work in every part of your backyard? Or does it have to be in a specific place? Use your sundial to keep track of time. How many hours have you played outside?

Is the sundial useful for precise measurements, like whether or not it is your turn for the swings or how long it takes you to run from one end of the yard to another? Would another type of early, low-tech clock work better to keep track of shorter periods of time?

While you are outside playing, consider this: Does time really go faster when you are having fun?