When Memorizing Causes Confusion

A few days ago there was a good day for watching the Moon. The sky was crystal clear and the Moon was a quarter. One of the cool things about a quarter moon is that it spends about half its time in our daytime sky and half in the nighttime, so we get to see it for quite a few hours if we’re looking for it. We were on a long car trip and I noticed it both in the early afternoon and again late at night. Do you know what I never saw…?

This...



The textbook version of what a quarter moon is supposed to look like.

Perhaps if I’d been paying better attention, perhaps if I had stopped what I was doing and checked out the Moon right at sunset I would have seen that, but I didn’t. And I missed it.

So what did I see? These top three images Midday (top), Just before sunset (middle), and Late evening (bottom).

And, I’m in the northern hemisphere, the place for which so many of the textbooks are written. Good thing I don’t live in the southern hemisphere, or I would have seen the Moon as shown in the bottom three images and then I would have been thoroughly confused.


When we tell kids what they should be seeing more than we ask them to see and observe, we do them a disservice. At best we rob them of a chance to make some pretty cool discoveries; at worse we confuse them when our scripted answers don’t match their reality. As teachers it can be tempting to distill information for students that we know they are going to be tested on… If we only give them the specific items, we reason, they won’t be confused.


In the case of moon phases, we rob them of the opportunity to learn the logic of what’s going on. Here’s a quick exercise you can try the next time you see the Moon in the daytime sky. With one arm outstretched, point to the Moon and with your other arm, point to the sun. The angle between your arms will tell you the phase the moon is in and give you a sense of where the sun and Moon are in relation to each other if you could view them from space.


So on the day I saw the quarter moon, my arms would have made a 90˚ angle with each other; if the Moon were a crescent, the angle would have been acute; if the moon is gibbous, obtuse; and if the Moon is full, 180˚ And had the Moon been new, the angle would be zero since a new Moon tracks with the sun. And what about waxing or waning? Well, if it's ahead of the sun, meaning the Moon sets first, then it’s waning; and if it's behind the Sun, meaning it will set last, then the Moon is waxing.


I wrote a classroom simulation to help kids envision what’s going on. If you’re interested, you can check it out by clicking here.


And if a video is more your speed, you can click here. Happy moon watching!

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