For some reason, I’ve got it stuck in my head that I’m going to teach my kids, from the very beginning, about the stages of the moon. I think it would be so cool to hear a tiny human voice say, “Look mama! A waning crescent moon!”
With that in mind, any time we see the moon, I try to mention the shape and phase (when I know it). Both kids know the word crescent, though they use it to mean anything that’s not a full moon. A full moon is a “moon”, and everything else is a “crescent moon”, whether or not it actually is a crescent moon.
Which brings me to the nerdy vocab lesson section of today’s post. I’m guessing you already know the terms waxing and waning, referring to whether the moon is getting bigger or smaller. (From Reference.com: When something is waxing, it is getting closer to its maximum property. When something is waning, it is decreasing, or getting closer to its minimum property. A personal example: While my pregnant belly waxes, my energy wanes. My energy level is dangerously close to its minimum property.)
Do you also know the term describing the phase when the moon is larger than a half moon but less than a full moon? And do you know how to tell, just by looking at the moon on a single night, whether it is waxing or waning?
Here’s the word I’ve tried a thousand times to get my kids to say:
gibbous: 1a : marked by convexity or swelling b of the moon or a planet : seen with more than half but not all of the apparent disk illuminated 2: having a hump : humpbacked
But they refuse! Every time I point out a gibbous moon to them, they always “correct” me and insist that it’s a crescent. Considering I didn’t start regularly using the term gibbous until I was in my thirties, it might be a while before they catch on.
So you probably knew that already, didn’t you? I think it’s one of those words that’s part of most people’s passive vocabulary: meaning we know the word but we don’t actively use it. Now, did you know that there’s a word for the line between the light and dark part of the moon?
terminator: 1: the dividing line between the illuminated and the unilluminated part of the moon’s or a planet’s disk (from Webster.com)
I’m willing to bet that terminator is new to you; I only learned it in writing this post. Now, how can you glance at the moon and determine whether it’s waxing or waning? Here’s a tip (taken from WikiHow):
A waxing moon will be illuminated on the right side, and a waning moon will be illuminated on the left side.
Hold out your right hand with your thumb out, palm facing the sky. The thumb and forefingers make a curve like a backward C. If the moon fits in this curve, it’s a waxing moon (increasing). If you do the same with your left hand and the moon fits in the “C” curve then it is waning (decreasing).
So there you have it. You’ve learned something new, and now you have something to do on these loooong winter nights.
Photos by Nousnou Iwasaki and NASA.