# Measuring the Diameter of the Sun and the Moon

 Areas of Science Astronomy Difficulty Time Required Short (2-5 days)
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## Abstract

You can measure the diameter of the Sun (and Moon) with a pinhole and a ruler! All you need to know is some simple geometry and the average distance between the Earth and Sun (or Moon). An easy way to make a pinhole is to cut a square hole (2-3 cm across) in the center of a piece of cardboard. Carefully tape a piece of aluminum foil flat over the hole. Use a sharp pin or needle to poke a tiny hole in the center of the foil. Use the pinhole to project an image of the Sun onto a wall or piece of paper. Use a ruler to measure the diameter of the projected image. Use your knowledge of geometry to prove that you can calculate the diameter of the Sun using the following proportionality:

The equation for measuring the diameter of the sun. The diameter of the sun divided by the distance from the sun to the Earth is equal to the diameter of the image of the sun through a pinhole divided by the distance of the pinhole to the image.

Important Safety Note: Never, ever look directly at the Sun. You can permanently damage your eyes (UC Regents, 2001).

## Bibliography

UC Regents, 2001. "Finding the Size of the Sun and Moon," The Center for Science Education @ Space Sciences Laboratory, University of California, Berkeley [accessed July 31, 2006] http://cse.ssl.berkeley.edu/AtHomeAstronomy/activity_03.html.

## Share your story with Science Buddies!

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### MLA Style

Science Buddies Staff. "Measuring the Diameter of the Sun and the Moon." Science Buddies, 12 Jan. 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Astro_p026/astronomy/measuring-the-diameter-of-the-sun-and-the-moon?fave=no&isb=cmlkOjk1OTc1NTIsc2lkOjAscDoxLGlhOkFzdHJv&from=TSW. Accessed 20 June 2021.

### APA Style

Science Buddies Staff. (2020, January 12). Measuring the Diameter of the Sun and the Moon. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Astro_p026/astronomy/measuring-the-diameter-of-the-sun-and-the-moon?fave=no&isb=cmlkOjk1OTc1NTIsc2lkOjAscDoxLGlhOkFzdHJv&from=TSW

Last edit date: 2020-01-12

## Experimental Procedure

For this science project you will need to develop your own experimental procedure. Use the information in the summary tab as a starting place. If you would like to discuss your ideas or need help troubleshooting, use the Ask An Expert forum. Our Experts won't do the work for you, but they will make suggestions and offer guidance if you come to them with specific questions.

If you want a Project Idea with full instructions, please pick one without an asterisk (*) at the end of the title.

## Share your story with Science Buddies!

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

## If you like this project, you might enjoy exploring these related careers:

Career Profile
Astronomers think big! They want to understand the entire universe—the nature of the Sun, Moon, planets, stars, galaxies, and everything in between. An astronomer's work can be pure science—gathering and analyzing data from instruments and creating theories about the nature of cosmic objects—or the work can be applied to practical problems in space flight and navigation, or satellite communications. Read more