Moon Not Shining of Its Own Light
I was reading Becky’s beautiful book (Our Moon, you know the one, lead review in the NYTimes Book Review, longlisted for the National Book Award) and she was talking about how ancient people figured out amazing things about the moon. And by the way, ancient people figured out amazing things in general, like the circumference of the earth and the existence of atoms, getting it wrong half the time and the other half, stunningly right. I mean, left to me, humanity would never know the stars were there during the day, would still think the sun moved across the sky. Anyway. Becky said that one thing the amazing ancient people figured out was that the moon shone, not of its own light but from light reflected from the sun.
She explained how they figured it out, and how you can figure it out for yourself — it has to do with sunrise or sunset. She said that once you see it, “it’s obvious.” So I tried. I looked at the moon, looked at where the sun had set, and it wasn’t obvious. I texted my neighbors who are curious and science-minded people, and after a number of texts over a number of days and little or no response, I decided they also didn’t think it was obvious, or maybe they just didn’t care. How could you not care that you, your own self, using nothing but the evidence of your senses, can figure out that the moon shines because it’s reflecting the sun?
So every night I kept looking at the moon. It goes all over the sky, did you know that? sometimes here, sometimes there, no telling where. I looked at the quarter moon, the half moon, the morning moon, the twilight moon. And one day, looking at the half moon, I could barely see the unlit half but clearly the lit half was facing the sunset. And I saw every day, quarter moon, half moon, the least sliver of a moon, always the lit side facing the sunset, or sometimes the sunrise, like the moon was looking at the sun, or actually the sun was looking at the moon. I mentally deleted the earth and the stars, and there was the sun, shining, with the moon in its way. The only part of the moon that shone was the part looking at the sun, the moon wasn’t shining on its own.
Well, this qualified as an epiphany and I can tell you, I felt pretty smart. I kept trying to find people to tell and though I told them, they were no more excited than my science-curious neighbors had been. Those particular neighbors are in fact interested in the moon; they routinely text me moon alerts — GO OUT & LOOK AT THE MOON, IT’S SO BRIGHT!. I couldn’t tell them about my epiphany because at that moment they were out on the west coast — we live on the east — and I was thinking we couldn’t do moon alerts, let alone epiphanies, until they got back east. Until I realized that the west coast has the same moon as the east.
So this is just to say, don’t go upgrading your opinion of my smartness any time soon. But really, go look at how the lit side of the moon faces the setting or rising sun. Once you see it, it’s obvious.
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Photos: the moon in Tuscany, by Antonio Cinotti, via Flickr Creative Commons. Sunrise, the moon, and the Matterhorn, by Devil Dancer, via Wikimedia Commons