Sun–Earth Motion Activity
Create your own primitive sundial! In this activity, the apparent motion of the Sun and Earth will be recorded and compared.
- Sun movement
- Earth movement
Does the Earth rotate around the Sun? As we look in the sky each day the Sun can be seen rising in the East and setting in the West. Is it the Sun or the Earth that is really moving? The Sun appears to move in the sky due to the movement of the Earth spinning around an imaginary line called an axis. The rotation of the Earth around its axis is what causes day and night to occur. The Earth travels around this axis in a counterclockwise manner. As the Sun first rises in the morning it seems to travels across the sky until it sets at night. Night occurs because the area of Earth experiencing nighttime has rotated away from the Sun. The Earth continues to rotate until the Sun comes into view again the following morning. One complete rotation of the Earth takes about 24 hours and is called a day. Earth completes 365 of these rotations in one year.
In ancient times, it was observed that shadows cast by trees, rocks, and other objects were very long in the morning and grew shorter and shorter until they disappeared when the Sun was directly overhead in the middle of the day. It was also noticed that the shadow was longer once again after the middle of the day and up until the night. Ancient people eventually realized that they were able to tell how much of the day remained by looking at shadows. The first time-telling device was most likely invented by a person who put a stick in the ground and made marks in the dirt to show where the stick’s shadow was located throughout the day. This “shadow stick” was the earliest form of a sundial and was known as gnomon (pronounced no mon; Greek for the “one who knows”).
Ancient Egyptians built stone towers called obelisks (also known as Cleopatra’s needles) that were used to tell time. Around 1500 BC smaller Egyptian sundials were also created and commonly used. In the Middle Ages, peasants in northern Europe carved sundials on the bottom of their wooden clogs. To tell time, the peasant would take off his or her shoe and stand it up facing the Sun. The hour was told by the shadow the heel cast on the dial. During the Renaissance period, sundials changed very rapidly. Many different styles and designs of sundials were created. In addition to having hour and minute marks for telling time, other features such as markings for seasons, calendars, and times of sunrise and sunset were added to sundial designs. Today, sundials are mainly used for decoration rather then a way of telling time. In this activity, a primitive sundial will be created to further understand how the Earth rotates and the Sun appears to move through the sky.
Paper with one punched hole
Wood dowel rod
Construction of the Sundial
- Obtain the wood dowel rod, wood board, pin and paper punched with one hole.
- Place the paper on top of the wood board so the hole lines up with the hole in the wood board (see Figure 1).
- Place the wood dowel rod through the hole of the paper and into the hole in the wood board (see Figure 2).
- Stick the pin into the center of the top end of the dowel rod (see Figure 2).
- Tape the paper to the wood board so it is secure.
- Take the sundial outside on a sunny day. Align the sundial so that the shadow of the wood dowel rod and pin extends across and is perpendicular to the paper (see Figure 3).
- Obtain a magnetic compass and place it next to the shadow of the wood dowel rod and pin. Using a pencil, record the directions North, South, East and West on one of the corners of the paper (see Figure 4).
- Notice the shadow created by the head of the pin. Using a pencil, place a dot at this point. Record the current time (to the minute) next to the dot. Do not move the sundial after the first dot is made!
- Wait five minutes and, using a pencil, mark a dot at the new location of the pin’s shadow. Record the new time (to the minute) next to the dot.
- Wait five more minutes and repeat step 5.
- Continue marking new dots for a total of 30 minutes. A total of seven dots should be marked and labeled with the appropriate time.
- Remove the wood dowel from the wood board.
- Remove the piece of paper from the wood board. Using a ruler and a pencil, draw a line connecting all seven of the dots. Draw an arrow showing the direction of movement of the shadow (see Figure 5).
- Using a ruler, measure the length of the shadow from the center of the hole of the paper to the marked dot. Record this value (in cm) in the data table.
- Measure and record the distance from the center of the hole in the paper to the last marked dot. Record this value (to the nearest 0.1 cm) in the data table.
- Measure the length of the line connecting all of the dots. Record this value (to the nearest 0.1 cm) in the data table. This line represents the distance the shadow moved in 30 minutes.
- Answer the Post-Lab Questions.