Modeling the Reasons for the Seasons
Name___________________________ Group______
Period______ Date______
Purpose: The purpose of this activity is to determine the distance to the Sun throughout the year using
photographs of the Sun and examine the reasons for the seasons after plotting this data.
Hypotheses: Examine the two pictures of the Sun below that were taken six months apart with the
same camera, at the same time of day, at the same location on Earth and answer the following
questions.
A
B
Q1: Are the images of the Sun the same size? Which one (A or B) is larger?
Q2: Describe at least one reason for this size difference.
Q3: In which month of the year do you think picture A was taken? In which month was picture B
taken?
Q4: In which month(s) of the year is your weather the warmest?
Procedure: 1. Click on “Image 1.54” in the At Ease menu for ESS (it looks like a microscope).
2. Select the File menu and Open... Double-click on the folder ESS Computer Files, then double-click
on the SunPics folder. A list of 12 different pictures of the Sun will appear. Each file name gives the
date on which the picture was taken. Open up the first one (01/7/98) by double-clicking on it.
3. Use a Metric ruler to measure the horizontal width of the Sun picture in Centimeters. Measure to
the nearest tenth of a centimeter or better. Make sure you are measuring the widest part of the picture
which is exactly across the center. Record your measurement in the data table below.
4. Close this file by either clicking the small white square in the upper left corner of the picture or
selecting Close from the File menu.
5. Repeat steps 2 through 4 with the next Sun picture until you have measured all 12 Sun pictures.
6. Using the actual diameter of the Sun, a conversion factor can be calculated that can be used to
determine the distance to the Sun from your measurements. This conversion factor is 2.085 x 109 or
2,085,000,000 km.cm. Divide this conversion factor by each measured Sun picture width and enter the
result in the data table below. Show your work for the first calculation below. If you have trouble
entering the conversion factor into your calculator ask for help!
(2.085 x 109)  (Measured Width) = Distance to Sun
7. The results of your calculation give the distance to the Sun on each date in kilometers. It will be
easier to graph your results if you convert them to millions of kilometers (megakilometers or
gigameters!) To do this you can move the decimal place to the left 6 places (or subtract 6 from the
exponent if you wrote it in scientific notation). Convert each result from step 6 and enter it in the data
table. The example below may help you with this step.
150,000,000.0 km = 150.0 million km or:
1.5 x 108 km = 1.5 x 102 million km = 150 million km
Date
mm/dd/yr
01/07/98
02/10/98
03/16/98
04/06/98
05/01/98
06/08/98
07/07/98
08/11/98
09/03/98
10/14/98
Measured Distance
(cm)
Distance to Sun
(km)
Distance to Sun
(million km)
11/12/98
12/14/98
8. Examine the graph paper supplied with you lab sheet. This is known as polar graph paper. The dates
are marked along the outside of the circle with time increasing as you go counter-clockwise. Distance
from the Sun starts at zero in the center and moves out as the distance increases. Each dark black circle
represents 10 million km from the Sun. Label each dark circle out from the center in millions of km
(10...20...30...etc.). If you do this correctly the outside circle will be 160 million km.
9. Graph the 12 distance to the Sun Vs Date points on the polar plot. Find the date of each point on the
outside of the circle (estimate it as close as you can). Move inward from this point and mark a point at
the correct distance from the center of the circle. Be careful and double-check each point.
10. When you have marked each point you are ready to draw a smooth curve through your points. This
curve will represent an accurate plot of the Earth’s orbit if you draw the curve smoothly, do not
connect the points with straight lines. When you have finished, answer the questions below.
Q5: According to your graph and the smooth curve you drew, is the Earth’s orbit more like an ellipse
or a circle?
Q6: According to your graph, in what month is the Earth the farthest from the Sun?
Q7: According to your graph, in what month is the Earth the closest to the Sun?
Q8: Revisit your answers to Q2 through Q4. (Don’t change your original answers, they won’t be
marked wrong). Which month was picture A taken in? Picture B?
Q9: When the weather in your area is the warmest, is the Earth closer or farther from the Sun than the
rest of the year?
Q10: How would you answer Q9 if you lived in Australia?
Conclusion: Most areas of the Earth experience four seasons during the year. Many people believe that
they are caused by the changing distance of the Earth to the Sun. Explain why you can reject this
hypothesis and why. Give at least two explanations for why this cannot be the reason for the seasons.