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Physics Puzzler

Loopy Physics

Celestial Textbook Misconceptions


Donald Simanek, Emeritus Professor of Physics, Lock Haven University of Pennsylvania

Our closest celestial neighbor, the Moon, presents two puzzles for your consideration.


01 Physics textbooks are lavishly illustrated, which is one reason they cost so much. But illustrations can mislead. Here's one from a 1997 book by a major university publisher. The accompanying description reads:

Fig. 1. Path of Earth and Moon?...both the Earth and the moon are in nearly circular orbits about the sun. They perturb each other's orbits—viewed from the sun, the moon performs a tiny "rosette" about the Earth's orbit (see Figure 1).

Even text can mislead. You can see why we do not credit the source, for the authors and publisher would likely rather remain anonymous. What is wrong with this diagram and this text? (There may be several errors.) How should these be corrected?

02 Standing on the Earth at the equator, are you closer to the Sun at high noon at the time of new moon, or at high noon a half-month later at the time of full moon? Why?

Ready for the answers? See "Loopy Physics: The Answers."

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