TEACH!: Unit 2, Lesson 2.

Supplies

• Flashlight
• Piece of graphing paper
• Pencil
• 3 identical Celsius thermometers (glass or metal backed, alcohol filled)
• Reflector lamp with clamp and 60 watt bulb
• Ring stand with iron ring
• Utility clamp
• Black construction paper
• Stapler
• Books or something else to prop up thermometers
• Meter stick
• Scissors

Background

Incoming energy from the sun can affect the heating of the Earth’s surface. The temperature of the earth’s surface at any given location is determined by two factors (among others): (1) The amount of energy received (direct/indirect radiation from the sun) and (2) the length of time a given location is exposed to the energy.

Since the tilt of the Earth ensures that this radiation from the sun arrives at different angles and for different lengths of time throughout the year, average global surface temperatures (and seasons) change! The tilt of the Earth does not have the same effect on all parts of the globe. Specifically, the change in the number of hours of daylight at the equator is small, but the change in the number of hours of daylight at the poles is large. At the pole, the Sun sometimes does not set at all, while other times it does not rise!

Although the poles sometimes receive 24 hours/day sunlight, they are not the hottest places on earth because of an important factor – the angle at which sunlight strikes the Earth. Because the axis of the Earth is tilted to 23.5 degrees, and because the Earth is not perfectly round, sunlight will strike the Earth’s surface at different angles, in different places, and in different times.

Activity A

1. Hold the flashlight close (10-15 cm) and perpendicular to the graph paper. Trace the outlines of the beam striking the surface in pencil. Record the surface area (count how many squares of the graph paper are included within the outline).

2. Slowly tilt the paper. KEEP THE FLASHLIGHT IN THE SAME PLACE. Occasionally (but at minimum three times) trace the new area covered by the beam. Record the surface area (count the squares).

3. After recording at least three surface areas, graph the progression of the surface area as you tilted the paper from its starting position perpendicular to the flashlight. It might look something like this:

Figure: Illuminated Surface Area: Bar Graph belongs here.

Graph text: In this example graph, you can see how the surface area of the illuminated space on the paper increases as the paper is tilted away from its initial position perpendicular to the flashlight.

4. Answer the following questions:

     a. If you continued this demonstration and tilted the paper to a ~30 degree with the flashlight, what do you predict would happen to the amount of area that was illuminated? (It would increase!)

     b. As the surface area covered by the beam of light increases, how does the energy from the flashlight change? (The energy from the flashlight becomes less intense because it is spread out over a larger area!)

     c. Two factors are crucial for determining the temperature of the Earth’s surface and/or atmosphere. What are these two factors? (Day length and the total amount of energy received from the Sun!)

     d. If a given location receives direct light from the sun, will it be warmer or cooler than a location that receives indirect sunlight? (It will be warmer than the location that received indirect sunlight!)

     e. If a location receives sunlight for 10 hours, while another location receives the same intensity of sunlight for only 4 hours, which location will be warmer? (The location that received 10 hours of sunlight will be warmer!)

Activity B

1.  Use black construction paper to make a cover for the bulb of each thermometer. It will work well to make a closed-bottom pocket/sleeve to slip each thermometer into.

2. Prop the thermometers up in the following way: one thermometer should be vertical. One should be slanted at about 45 degrees, and one should be horizontal. Make sure you can easily read the thermometers without touching them in the experiment.

3. Attach the lamp to a ring stand. Make sure it does not move during the experiment. Adjust the lamp so that its bulb is centered 40 cm above the bulbs of the thermometers.

4. With the lamp off, record the temperatures of all three thermometers . This is the temperature at “Time 0”.

5. Turn on the lamp and record the temperature of each thermometer every 5 minutes.

6. Using graph paper, plot temperatures versus time for each thermometer. Make sure you can tell a difference between each thermometers line in the graph (use different colors or lines). It might look something like this:

Figure: Temperature vs. Time Line Graph belongs here.

7. Answer the following questions based on your data:

     a. Which thermometer showed the greatest temperature increase? Why?

     b. Which thermometer(s) best show how sunlight strikes at the equator?

     c. Which thermometer(s) best show how sunlight strikes at the poles?

     d. Which thermometer would represent the middle latitudes of the Earth?

     e. How can you explain why the equator is always hotter than the poles using your
data?

**These activities, questions, and text were obtained from the Sun Angle interactive lesson from the University of Utah’s Astrophysics Science Project Integrating Research & Education (ASPIRE) website (http://sunshine.chpc.utah.edu/labs/sunangle/sunangle.html )

Resources

University of Utah – ASPIRE interactive online science lessons and labs. http://sunshine.chpc.utah.edu/Tlessons.php

The University of Utah’s Astrophysics Science Project Integrating Research & Education (ASPIRE) program provides interactive science lessons and labs that teach students about astrophysics in a fun and easy to understand manner.

University of Harvard — Ch. 2 The Earth’s Orbit
http://hea-www.harvard.edu/ECT/the_book/Chap2/Chapter2.html