Name
Section
Date
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MEASURING THE DIAMETER OF THE SUN
Even though the Earth is nearly 150,000,000 kilometers from the sun at its
closest approach, it is still possible to make accurate measurements of the
sun’s size by using instruments. In this investigation you will construct a
simple device and use it to collect data that will allow you to calculate the
diameter of the sun.
PURPOSE:
MATERIALS:
Meter stick
Scissors
Tape
Aluminum foil
Pin
Two 3X5 cards
Two screen supports for meter stick
PROCEDURE:
01. Use scissors to cut a square hole with sides about two inches long in
approximately the center of a 3X5 card.
02. Draw two parallel lines precisely 0.8 cm apart on the other 3X5 card.
03. Carefully tape a piece of aluminum foil over the square hole you made in
the first 3X5 card.
04. Use a pin to make the smallest hole you can at about the center of the
aluminum foil.
05. Place a screen support on the meter stick near the end with the lower
numbers.
06. Place the 3X5 card with the pinhole on that screen support.
07. Place the other screen support on the meter stick near the end with the
higher numbers.
08. Place the 3X5 card with the parallel lines in that screen support with the
lines facing the other card.
09. Aim the end of the meterstick that has the aluminum foil-covered card
on it toward the sun. (CAUTION: Do not look at the sun; you may
damage your eyes.) Move the meterstick around until the shadow of the
card with the aluminum foil covers the other card. A bright image of the
sun will fall on the card with the parallel lines.
10. Move the card with the parallel lines until the image of the sun precisely
fills the space between the lines.
11. Determine the distance between the cards to the nearest 0.1 cm and
record it in the data table. Also record the diameter of the image. (You
knew the diameter of the image before this last step: THINK ABOUT
IT.
OBSERVATIONS: (remember: the observations must not be the data)
1.
2.
3.
DATA: (fill out this table)
Distance between cards
Diameter of the sun’s image
RESULTS:
01. Using the formula below, calculate the diameter of the sun.
Dia. of the sun (km) = Distance to the sun(km) diameter of the sun’s image(cm)
Distance between the two cards (cm)
NOTE: The average distance between the sun and the Earth is approximately
150,000,000 km.
Hint: let M equal “million” so that 150 M is the same as 150,000,000; this way you
can leave out the six zeros when you use your calculator to do this problem. When
you get your answer, add the M to it. So, if the answer is 2.3, add the M to get an
answer of 2.3 M, or 2.3 million.
02. The actual diameter of the sun is 1,391,000 km. Using the formula
below, determine the amount of error in your calculated value for the
sun’s, diameter.
Percent error = Difference between your calculated value X 100
Correct value
03. What could account for your error in calculating the sun’s diameter?
QUESTIONS:
01. How might the technique used in this investigation be useful in making
other astronomical measurements?
02. How is the technique used in this investigation related to the
construction
of a camera?
03. How might clouds in the sky affect the accuracy of your measurement in
this investigation? (be specific: saying “you can’t see the image clearly”
would not answer the question)
CONCLUSIONS: (summarize this method in one or two sentences,
discuss whether it was successful, and suggest a change in the procedure
which would make it more accurate)