We chose the measurement time of 12:05. On the measurement days, we set up the ladder about ten minutes ahead of time.
We traced a circle on a small piece of paper and wrote down the date and the time of 12:05. As the second hand approached the measurement time, we carefully went up the ladder. At the moment the second hand registered 12:05, we taped the piece of paper to the ceiling so that the spot reflected from the mirror was in the circle.
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We added red dots to the pieces of paper, and took this photograph of the ceiling to show how our analemma shape developed over six months. Imagine that you have turned toward the south-facing window and are looking straight up at the ceiling. The dots at the bottom of the photograph are nearer the window than the dots at the top. You can see how the path travels over the ceiling tiles and recessed light fixture.
The dot at the top of the photograph is for January 2, and the dot at the bottom (beneath the light fixture) is for June 3. Notice how the four bottom dots are offset. Why do you think this happened?
We think the explanation is…
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The Noon Day Project uses a technique similar to the outdoor version of this activity to figure out the size of the Earth. It is based on a method performed by Eratosthenes, the director of the famous library in Alexandria, Egypt, more than two thousand years ago. Find out more… |
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