Sunlight Angles Lab
Background: The position of the sun in the sky affects the angle of sunlight and therefore the transfer of
solar energy. Energy from sunlight is not spread evenly over the Earth. At any given time, half of the Earth is
in darkness, receiving no solar energy at all. On the daylight side, only the point directly under the Sun
receives full-intensity solar radiation. Throughout the day, the total amount of solar energy remains the same,
but the intensity changes. From the equator to the poles, the Sun’s rays meet the Earth at smaller and smaller
angles and the light gets spread over larger and larger areas. The angle at which solar radiation strikes the
Earth affects the amount of energy received by the surface. Solar intensity, or the amount of solar energy per
unit area, is determined by the angle of the Sun in the sky. Solar intensity increases when the Sun is high in
the sky and decreases when the Sun is closer to the horizon. When the Sun is directly overhead at a 90˚ angle,
sunlight strikes the surface directly, maximizing solar intensity. As illustrated by figure 1 below, if the Sun is
directly overhead, 1 square mile of sunlight will cover one square mile of ground. However, the lower the Sun
is in the sky, the further its rays must spread, covering a greater distance at a lower intensity. Figure 2
demonstrates why winters in temperate regions are considerable lower in the winter than the summer. Since
lower winter sun angles cause less solar energy cause less solar energy to be transferred to the ground, less
heat is radiated into the air around you in the winter. That’s why even a sunny winter day can be cold!
Figure 1
Figure 2
Vocabulary Review Pre-Lab:
1. Solar Energy
a. Height of the Sun in the sky (measured in degrees)
2. Solar Intensity
b. Earth’s axis is tilted neither towards or away from the Sun
3. Sunlight Angle
c. Where the Sun rises in the East and sets in the West
4. Season
d. Heat transfer by electromagnetic waves
5. Solstice
e. Short-term periods of climatic change
6. Equinox
f. The amount of solar energy per unit area
7. Altitude
g. Utilization of radiation from the Sun
8. Horizon
h. Earth’s axis is tilted most towards or away from the Sun
9. Zenith
i. How directly the Sun strikes the Earth (measured in degrees)
10. Radiation
j. Sun’s highest point in the sky
Sunlight Angles Lab
Hypothesis: How does sunlight angle affect solar intensity?
Materials:
 Flashlight
 Grid paper
 Computer paper
 Protractor
 Ruler
 Pencil
 tape
Procedure:
Part 1—Making a focusing hood for your artificial Sun
1. Wrap the piece of paper around the bulb end of your flashlight to make a tube with the same diameter at
both ends. The paper should extend at least 3 inches beyond the flashlight.
2. Tape the tube securely to the flashlight. When you turn on the flashlight and shine it on your desk, you
should see the edge of the beam clearly.
Part 2—Simulating solar intensity
1. Place your grid paper on a flat surface. Have a lab partner hold the flashlight directly above the grid paper.
The end of the paper hood should be 2 inches above the paper. The flashlight and hood should make a 90°
angle with the paper. Check the angle measure with your protractor.
2. Have the other lab partner carefully trace the outline of light on the paper. Label this circle 90°.
3. Each square on the graph paper represents 1 cm2. Count and record the number of square centimeters
within your outline.
3. Calculate the percent of the grid paper covered by the sunlight by dividing the number of squares within
the 90˚ outline by the total number of squares on the grid. Record this percent in your data table.
4. Tilt the flashlight until it makes a 75° angle with the paper using a protractor to measure the angle. Trace
the outline of the light and label the outline 75°. Count the squares, calculate percent coverage, and record.
5. Repeat the procedure for 60°, 45°, 30°, and 15°. If the light shines off the edge of the grid paper, move the
flashlight so that as much of the light as possible is on the paper. You may have to estimate percent coverage
for later trials.
Data:
Percent Coverage
Angle
Area of paper
Area of grid paper
(Area illuminated/
illuminated
Area of grid paper)
Sunlight Angles Lab
Analysis:
Imagine that there are 100 particles of light coming out of the flashlight as it is on. Think about how much
light is given to the individual squares at each angle. Which gets more light per square (greater solar intensity)?
Use the formula below to calculate solar intensity.
100 particles / ____ squares illuminated (area) = _____ particles / cm2
Graph the change in solar intensity from most direct to last direct angle.
1. Based on your graph, do your results match your hypothesis?
2. What do your results tell you about the differences in sunlight angle and solar intensity throughout a
day?
3. What do your results tell you about the differences in sunlight angle and solar intensity during
different seasons?
Sunlight Angles Lab
4. If light is also heat energy, what treatment receives the most heat per square? The least?
5. Label the regions above: tropics, temperate, polar
a.
What region receives the most direct sunlight? Why?
b. What region receives the least direct sunlight? Why?
c. Which region experiences the greatest solar intensity? The least?
d. Which region receives the most heat per area? The least?
Lab Report Rubric
Illustrated Title Page _____ of 5 points
+ Name, date, and class
Each of the following sections should be included in your formal lab report. Write in complete sentences, unless otherwise noted.
Introduction
_____ of 10 points
State the question or problem. List or write sentences defining each of the following:
Hypothesis
_____ of 5 points
Variables
_____ 10 of points
Independent, Dependent, and Controlled
Write 1-2 sentences that explain the rationale behind the experiment (how it relates to class).
Materials and Methods_____ 10 of points
List materials used and write methods in a numerical, step-by-step format such that someone could repeat it.
Write down EXACTLY what you did.
Data _____ 40 of points
Include your data table, calculations, and graph here. Write 1-2 sentences about what each one shows. Show
all work and be sure to label both your figures, as well as the axes of your graph.
Analysis & Conclusion
_____ 20 of points
Use complete sentences to answer the analysis questions unless otherwise noted. The conclusion should
always describe what you LEARNED. Do not say that the lab was fun, stupid, boring, etc. State how your
findings reinforce concepts from class and the real life application of what you did.