PhysicsLAB Lab
The Size of the Sun

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Utilizing a solar eclipse, produced when the Moon blocks our Sun’s light, the Greeks were able to make an estimate for the size of the Sun. To view video details of the total solar eclipse in the Gobi desert of northwestern China near the Mongolian border on August 1, 2008, click on the following link.

1999 Solar Eclipse in France - images courtesy of Luc Viatour
Using the following diagram as a guide, construct a ratio of corresponding parts of similar triangles that will enable you to calculate the radius of the Sun.
Remember that the radius is one-half of the diameter of a circle or sphere.

Refer to the following information for the next four questions.

In this next section, substitute these  astronomical values (link) into your ratio to geometrically determine the average diameter of the Sun. Remember that you must reduce all values to the same common metric prefix (link) .
  • average distance from Earth to Moon - 3.844 x 102 Mm
  • average diameter of the Moon -  3.476 km
  • average time for light to travel from the Sun to the Earth - 8.311 minutes
What is the distance from the Earth to the Sun to four significant figures

Calculate the diameter of the Sun to four significant figures. 

Today we know that the average Sun's diameter is approximately 1.392 Gm. To four significant figures, what is the percent error for your calculations? 

Based on the ratio of the Sun's diameter to the Earth's diameter, how many "Earths" would fill the volume of the "Sun?" Explain your answer.

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William A. Hilburn
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