PhSc 206
The Noontime Sun
Name/Section
_______________________________ Name/Section
_______________________________
Name/Section
_______________________________ Name/Section
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You should try to do this lab with one or two other students.
Make the following observations. Be careful when
looking
towards the
sun. Never look directly at the sun without appropriate
protection.
(You can use the solar filter available at the bookstore.)
Remember - those are your eyes. (If you feel
uncomfortable
viewing,
there is probably a reason for that!)
Do these observations between 12:00 and 1:00 P.M.
1. Compare the diameter of the Sun to the width of your index finger
held at arm's length.
Which is bigger? ____________________________
The Sun is almost exactly 1/2 degree in diameter.
How wide (in degrees) is your index finger when held at arm's length?
_____________________________
How wide (in degrees) is your index finger when you hold it only
halfway out?_____________________________
2. Estimate the angle that the Sun makes with the ground when
it
is at the highest point during the day. To do this, go
outside
between noon and 1:00 pm. Estimate the number of degrees off
the
ground the Sun is (use the point on the horizon closest to the
Sun). A fist, held at arm's length away from your head, is
about
10 degrees across, and your pinky finger (again at arm's length) is
about 1 degree across. The Sun and Moon are each about half a
degree in diameter. Record the date and exact time for each
observation. Try to accurately measure the angle off the
actual
flat horizon, i.e., where the horizon would be if there were no
mountains.
Date: ______________________
Time: _______________________
Height: _______________________ (fist and finger widths)
Height: _______________________ (degrees)
3. During your noon solar observation, measure the length of
the
shadow of a vertical stick of known length. A ruler works
great
for this, since you know it is 12 inches long. Then you can
measure the length of the shadow using the ruler. Which is
longer, the vertical stick or the shadow? Divide the length
of
the stick by the length of the shadow to find the ratio:
Length of stick: ___________________ (cm)
Length of shadow: ___________________ (cm)
ratio = (length of stick)/(length of shadow)
What is your ratio? (Round your answer to three significant
digits.)
ratio: _________________________
This ratio is the tangent of the angle that the sun makes over the
southern horizon. Use the inverse tangent (arctan, or tan-1)
key
on your calculator to convert this ratio into an angle:
angle = tan-1(ratio)
What is your angle?
(Make sure your calculator is giving you the answer in degrees and not
radians, and then round your answer to the nearest degree.)
angle: __________________________
4. Compare this angle to your fist-width estimate from problem 2
above. The answers should be close to each other.
Comment on the comparison:
Durango's latitude is about 37 degrees.
5a. What angle above the horizon should the sun be at noon on March 21 (the first day of spring)?_________________
5b. What angle above the horizon should the sun be at noon on June 21 (the first day of summer)?_________________
5c. What angle above the horizon should the sun be at noon on September 21 (the first day of fall)?_________________
5d. What angle above the horizon should the sun be at noon on December 21 (the first day of winter)?_________________