There is a short video called The Private Universe which shows a bunch of Harvard Graduates on graduation day. They are being asked questions about what causes the phases of the moon, and why are there seasons. Very few of them get it right. Most guess that the phases of the moon are caused by the earth's shadow, and the seasons are caused by how close the earth is to the sun.
After watching that video years ago, I decided that my kids would have a basic understanding of the whole process. I thought it would be a relatively simple thing. Explain it once, we're good to go.
For those that don't know (at least for us in the northern hemisphere) to tell you simply look at the line between light and dark. The line always moves from right to left. So if there is light on the right side, the moon is waxing. If the light is on the left side, it's waning. Another easy way to tell is if the moon comes up before the sun goes down, it's waxing. If it comes up after the sun goes down, it's waning. And if it comes up at the exact time the sun goes down, it's full.
I believe I've explained it close to 50 times now. And my favorite question when we're driving at night is, "Boys! Look at the moon, is it waxing or waning?"
What follows is quite humorous. Because they are boys, or maybe because they are my boys, they are incredibly competitive. It doesn't matter so much whether or not they get it right or wrong, but whether or not somebody else gets it right or wrong.
So, somebody will guess waning, and then several others will go along. Then somebody changes to waxing, and they all change back. Usually my wife guesses, and they will change to her guess. Then they remember that she very often guesses wrong, so they will go back to the original guess.
In the end, I tell them the correct answer, and they either all cheer or groan, but inevitably it ends up in a fist fight.
"I guessed waxing first."
"Yeah, but you changed your answer."
"Yeah, I changed it five times, and 3 times I was guessing waxing, so I was right."
"You're a stink pot!"
"You're a cotton headed ninny muffin."
And that is where it comes to blows. But I put up with the blows, because I want them to understand how things work. To know whether or not the moon is waxing or waning, you really have to think. You have to be able to picture how the universe works. It's a good exercise.
Anyway, the point of this post is that the other day I asked the question, waxing or waning? My oldest son asked, "which way is north?"
At first I didnt' see the significance of the question, but then realized that if the moon is directly overhead, and you don't know which way north is, you might very well guess wrong. I always know which way is north, so in my mind it wasn't part of the process. It was 'existing knowledge'.
So it was an exciting moment, because I realized he's getting it. He got the answer right, but I'm not sure if it was because he guessed correctly, or if he worked it out. We'll see how it goes the next time.