The Universe in the Classroom

What If the Moon Didn't Exist?

Worse Surfing There are many other differences between Earth and Solon that your students can discover, and there are innumerable other alternative Earths, several of which are in my book. Let me now turn to one way that I have effectively used what-if questions in grades 4-12 and college.

I normally begin by asking the class what they think would be different if the Moon didn't exist, or if the Sun were closer to Earth, or if a star exploded nearby. Here are common replies to the question, "What if the Moon didn't exist?''

After acknowledging these ideas, and correcting the wrong ones, such as the disappearance of tides, I present the major astronomical results:
  1. The day would be eight hours long.
  2. The winds would be much stronger.
  3. Complex life might not exist yet.
  4. When life did arrive, it would have a different biology.
By seeing these results up front, students begin to rethink their ideas to make sense of this new information. This is often disconcerting for them, but they are eager to understand how these ideas might be correct. Then I proceed to work through the properties of Solon described above.

I was delighted to learn that many middle-school and high-school teachers around the country are using What If the Moon Didn't Exist? to help to teach about Earth and space. Such projects are usually done in groups of three or four. It is useful to ask students specific questions about the alternative Earth. For example, "How would the temperature be different if the Sun were more massive?'' "What would happen to humans if the ozone layer were depleted by 25 percent?'' John Hilker in Union, Maine has his students explore such what-if questions; the scenarios they create are put on computer and videotaped. Hilker has offered to field your questions about this work. You can reach him at the A.D. Gray Middle School, P.O. Box 329, Waldoboro, Maine 04572.

In my college introductory astronomy course, I require students to write a short (2,000-word) term paper that does one of three things: explain in more detail (or even try to disprove) the science in one of the chapters of my book; extrapolate a scenario in a direction that I did not take it; or ask a new what-if question and explore some of its implications.

In using what-if questions in the classroom, it is worth bearing in mind that students extrapolating the effects of new scenarios will encounter two different situations: direct changes to the new version of Earth and indirect changes resulting from the direct changes. Direct changes result from the astronomical variation, such as Solon's more rapid rotation and lower tides. More challenging are the indirect changes, such as higher winds, slower evolution rate, faster biological clocks, and need for sturdy support against strong winds. Many secondary changes create other changes in turn, a hierarchy that can be explored with concept maps or flow charts.

To elicit ideas about indirect changes, I ask questions about the effects of the direct changes on specific things that exist today. For example, "What effect would the high, sustained winds have on oral communications on Solon?'' Well, we know from experience that high winds make speaking and listening hard. Therefore, maybe speech would not evolve on Solon. Perhaps an organ that changed colors or moved like a semaphore flag would become the preferred method of communication for advanced life forms, or who knows?

By making students aware of the power of asking, What if? we give them another intellectual tool to help them to cope with an increasingly complex world.

NEIL F. COMINS is a professor of physics and astronomy at the University of Maine in Orono. He is author of What If the Moon Didn't Exist? Voyages to Earths That Might Have Been and Discovering the Universe (fourth edition, with W.J. Kaufmann III). His email address is

(c) 1996 Neil F. Comins. All Rights Reserved. For further information about Comins and his work, please contact the Maria Carvainis Agency, 235 West End Ave., New York, N.Y. 10023; phone 212-580-1559.

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