A Model to Track the Sun's Apparent Movement Across the Sky
Background: Scientists say monarch butterflies use the sun as their clock and compass during migration. They have a mechanism called a "time-compensated Sun compass."
It’s hard to visualize this without a model, so try this activity. You'll need a sunny day, several trips outside, and a plastic dome. First find the direction to Mexico from your hometown. Draw an arrow on the dome to show the direction of flight to Mexico. Then, using the model, record how the sun appears to sweep across the sky during the day.
(Just think, monarchs know all of this by instinct! So even if you find this complicated, you’ll appreciate the challenges monarchs face when using the sun as a clock and compass! )
Each time you go outside, describe the direction you’d need to fly south to Mexico, in relation to the position of the sun. This chart illustrates the “flight instructions” you can imagine monarchs following at each time of day in order to orient southward:
| Local Time | Flying Instructions (in order to fly SOUTH) |
| 9:00 AM | Fly with the sun on my left. |
| 12:00 PM | Fly straight toward the sun. |
| 4:00 PM | Fly with the sun on my right. |
Materials:
- Clear 2-quart bowl
- Large sheet of white paper
- Sharp pencil
- Overhead marking pen
- Compass
Activity:
- Take all the materials outside. Find a level surface for the paper. Make sure the location receives sunlight throughout the day.
- Make an X in the center of the paper. This X will represent our Earth.
- Place the bowl (our atmosphere) upside down on the paper. Mark an x on the center of the bottom of the bowl with the overhead marker. Make sure the X on the paper is lined up under the x in the center of the bowl. Trace the edge of the bowl onto the paper to make it easier to line up.
- Using the compass determine North for your location. Mark North on the paper and on the bowl.
- Each hour, touch the side of the clear bowl with the tip of the pencil so that the shadow of the pencil's tip falls on the X on the paper. (You can put a small 1,2,3 etc. beside each dot so you'll remember the order in which you made the observations). To get accurate results the bowl must sit in the same location and be lined up in the same way for each hourly (and monthly reading).
- After making four or five marks determine which direction the sun is moving.
- Extention: Repeat this activity each month to show the changes in the angle of the sun throughout the year. Use one color overhead marker from Sept through December and another color from January through June. If this is done on or about the 20th of each month you will see the results on the fall and spring equinox and the winter solstice.
