170. Middle School Astronomy

We learn our astronomy from books, but that isn’t how the science started. The ancient Greeks learned about the stars by looking at the stars. Their understanding was a mixture of observation and myth, with myth sometimes predominating.

When we are young, we also learn astronomy from casual statements we hear from adults. I’ll give you an example. Mars has recently been at a close approach; every evening lately, when I step out my front door (miles from the nearest city) to look at the sky before bed, there it is, red and bright, about halfway to zenith in the south-eastern sky. Now imagine that I say to a child, “Mars is really getting close.” Just that, with no other comment. What images might pop into that child’s mind?

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“The seasons change because of changes in the Earth’s tilt.” You might find a statement like that in an old middle school science textbook along with an illustration like this:

ma1

Not true. Not a lie, but an oversimplification that may be fine for the average student, but does not do justice to the brightest kid in the room. A better statement would be, “The seasons change because of apparent I changes in the Earth’s tilt”, coupled with an illustration like this:

ma2

Now we are more accurate but we’ve confused 90% of the students.

It should be obvious by now that this is a bit of a how-to based on long experience. Even if you aren’t a teacher, you will probably someday have to explain this kind of thing to your own kids.

Let me suggest a third option. First explain things in your best lecture voice with reference to the textbook and with drawings on the board. Then pick a student sitting in the middle of the classroom; out of kindness, choose someone who likes attention. Say, “Helen, don’t move. For the next few minutes, your head is going to be the sun.” Then establish where Polaris lies, for the sake of the demonstration. Your classroom may not allow you to use real north. If some bright, smart-mouth kid catches you out, don’t get mad. Rejoice that someone is paying that much attention and make it a teachable moment.

Now walk around the classroom with the classroom globe tilted toward your Polaris and talk them through the seasons, pointing out that the tilt never changes in relationship to Polaris, but it appears to change in relationship to Helen, our sun. Pat your worst troublemaker on the shoulder as you pass him, wink at the shy girl in the back corner who never volunteers, and say, “Excuse me, Earth coming through,” when you have to dodge around desks.

There is a rule of thumb for teaching science (which probably doesn’t work for algebra). If you enjoy teaching, and you let your students enjoy learning, they probably will.

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That exercise was for letting students visualize things they can’t see for themselves. You can also help them see things that happen in their everyday world, but normally go unnoticed.

Observing the path of the sun through the seasons is an Earth’s-eye-view version of the tilted globe carried through the classroom. How do you compress a year’s worth of observation into one 40 minute session, using the real sun instead of charts and graphs? It can be done, but it takes nine observations on your part, spread over three days, with those three days spread over half a year. It also takes a small can of paint and a paintbrush.

When I set this up, I picked a solid, upright, eight foot steel pole which was set up away from the shadows of structures and which I knew would not be disturbed for years to come — a volleyball net pole out on the playground. At 10 AM, noon, and 2 PM (sun time, not daylight savings time) one summer solstice I painted three inch circles (same diameter as the pole) at the pole shadow’s tip.

I repeated those actions during the fall equinox, which was intriguing for my students. I had a paint can and small brush at the ready during my ten and two classes, and on the stroke of the hour, I ran out of the classroom, painted the circle, and ran back in while they watched from the windows. The noon painting had an even bigger audience because of noon recess. As you might guess, I told those who asked questions, “You’ll find out what this is all about — some day.” On Christmas break I painted the last three circles during the winter solstice.

That spring, and for years afterward, I arranged to teach solar motion as near as possible to the spring equinox. The solstices fall outside school days, and the fall equinox is often cloudy in California. I explained everything with lectures, and reading, and drawings on the board, but then we all went out to those nine circles on the playground. As I talked them through the lesson, we all watched the pole’s shadow move. It is fascinating in our mile-a-minute world to take the time to watch a shadow inch its way across the ground. Even if it wasn’t 10 or noon or 2, everyone could see that the shadow’s tip either had or would touch all three of the middle circles.

I explained how I had placed the circles and invited students to lie down with their head on a circle and look past the tip of the pole to see where the sun would be (or would have been) at noon or 10 or 2 on the first day of summer or the first day of winter.

They paid attention. On days they pay attention, learning happens. It isn’t easy, but it works.

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