Have you ever shined a flashlight against a surface in the dark. If you point the flashlight straight toward a wall, for instance, you'd see a small circle of light. But if you slant the flashlight upward, the circle gets larger.

In the same way, sunlight is more concentrated in one area when it hits the earth directly, and when the sunlight hits the earth at a slant, the sunlight spreads out, making it less intense.

In the following activity, ultraviolet will be referred to as sunlight.

Purpose of this activity

To learn about the angle of the sun to the earth and how it affects you.

What you will do

Observe and measure your own shadow. Choose a weekend to perform this activity when you'll be able to return to the same location throughout the day. If you're a child wishing to complete this activity and you need help, ask a parent or older brother or sister to assist you.

What you'll need

Measuring tape, notebook, pencil or pen, and chalk.

Procedure:

1. Begin this experiment around 8 or 9 a.m. on a sunny day.
2. Stand in the same place, your back to the sun.
3. Draw a circle around your shoes with the chalk.
4. Observe your shadow. Is it long or short?
5. Draw another circle around the head of the shadow.
6. Measure the distance from one circle to the next.
7. Write the time of day and the distance in your notebook.
8. Continue to do this every one or two hours until around 4 or 5 in the afternoon.
9. Record in your notebook what you observed about your shadow. For instance, did it get longer or shorter throughout the day or did it increase and then decrease in size? When was your shadow the longest? Shortest? Did it change direction?

What's happening

You observed the sun's movement as you were watching your shadow. When your shadow is long earlier and later in the day, the sunlight is less intense and at a lower angle. When sunlight is more intense between 10 in the morning and 4 in the afternoon, but particularly an hour before and after noon, try to stay in the shade and wear sunglasses, sunscreen, a hat with a wide brim and clothing that covers you.

Source

Ahrens, Donald C. (1991). Meteorology Today, 4th Ed. St Paul: West Publishing Company, 79-93.