Sundials are the
oldest way to tell time. The position of the sun changes during the
day. The sun doesn't move; the Earth rotates around the sun, making it
seem like the sun rises in the east and sets in the west. As the sun
goes across the sky, the post in the center of the sundial casts a
shadow on a circular plate. Marks on the plate tell you what time it
is. It's just like reading a clock!
To make your own
sundial, you need:
A large styrofoam
or paper drinking cup with a plastic lid and straw,
pebbles (enough to fill the cup about half full)
Now you are ready to build:
Use the pencil to
poke a hole in the side of the cup approximately 2 inches below the
Put the pebbles
in the cup so it doesn't tip over.
Put the lid on
Put the straw
through the hole in the cover and the hole in the side of the cup.
Let it stick out about half an inch from the side and tape the straw
to the cup.
building—Let's give it a try!
Start using your
sundial on the morning of a sunny day when you'll be home all day.
Find a spot out in the open that is sunny from 10 in the morning until
3 in the afternoon. Look for a good, open view to the South with no
trees or buildings in the way. Place the sundial on level ground or on
a level table.
Use the compass
to find North, and point the straw to the North. Now be careful not to
move the sundial. Just in case, you might want to make a mark near the
bottom of the cup and on the ground or the table, so you can line them
up again if they get moved. Or you can just line up the sundial to the
North again using the compass.
At 10 a.m., use
the marker to mark where the shadow from the straw falls on the lid of
the cup. Repeat this every hour until 3 p.m. Make sure your marks are
neat and straight. If you have to leave or if it clouds over, you can
always finish doing this a few days later—you don't have to do it all
in one day. Once you have marks for all the times, you're ready to use
the sundial. Wait until the next day and try reading the time by
comparing the shadow to the marks you made. How well can you tell what
time it is?