Why is the moon white and why does it have different shapes?
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Moment of Um comes to you from APM Studios. I'm Shayla Farzan. I love sitting outside at night staring up at the moon. It's so big and white and beautiful that it inspires me to write spontaneous poems like this.

Moon, oh moon, you are so round. If you were a pizza, I'd scarf you down. If you were a hoop, I'd hula you forever. In the alphabet of the sky, O is your letter.

Wait, hold up. The moon isn't round tonight like I expected. It's actually skinny and curved like a fingernail clipping. Hmm. I can work with that. Moon, you sneaky chameleon. You look different than I thought. You are full of surprises. Like a birthday pinot. To surprise.

Still, no matter your shape, your vibe is so pleasant, whether round like a ball or curved like a crescent. Hey, why does the moon change shape anyway? And why is it white? So much to ponder. I guess Eloise was waxing poetically about the moon too, because she sent in this question. Hi, my name is Eloise. I am from Billings, Montana, and here's my question.

Why is the moon white and why does the moon have different shapes? It turns out that the moon's shape is not actually what's changing. My name is Preston Dykes and I'm a science communicator who works at NASA's Jet Propulsion Laboratory in Southern California. The moon looks white or bright in the night sky because it's reflecting sunlight.

Just like a mirror reflects light, the moon reflects light from the sun. But if you were an astronaut standing on the moon's surface, you'd see that its surface is actually more of a dark gray color, kind of like pencil lead or an old dark gray road.

So you might ask, then why, if it's gray, does it look so bright and white from Earth? And the reason is that the moon is out there in space, and space is very dark. So when sunlight hits the moon, it bounces off the moon's surface and

shines toward us and our eyes then see a brightly lit moon lit up by the sun against the much darker sky of space. And that makes the moon appear white or bright against the much darker sky. So now, why does the moon seem to have so many different shapes? What we see is different parts of the moon being lit up by the sun.

So the moon goes around Earth in a big circle, and as it moves, we see different sides of it lit up by sunlight. Sometimes we see a big round moon. The entire side of the moon that's facing us is the part that's lit up by the sun.

Other times we only see a slim crescent moon or a half moon, and that's because part of the moon's sunlit side is not entirely facing us. Only part of the sunlit part of the moon is facing toward us. And so we see a different shape from here on the ground on Earth.

This is a pattern actually that repeats over and over again every month. So if you watch the moon every night, you can see these changes and we call them phases. These are the phases of the moon. The moon is always a big round ball of rock up there in the sky. But the part of the moon's surface that we're seeing lit up by the sun is the part that is changing. Um, um, um.

Oh, okay. So up close, the moon is gray, but it looks bright white to us because it reflects so much sunlight. And where that sunlight is on the surface of the moon changes.

changes how it looks to us. We're always looking up at the same side of the moon. And when the sun is shining right on it, we see a big, bright, full moon. But when the sun is mostly shining on the part of the moon we can't see, then the moon looks like a thin, curved letter C. So cool. You know, I feel inspired to write another moon poem.

Oh moon in orbit, I love you a lot. Whether round like a donut or curved like a croissant. Your looks are so good, your beauty beguiling. Staring at you always leaves me smiling.

If you like this episode, take a second to subscribe to Moment of Um wherever you listen to podcasts. And if you want to know what it would be like to stay at a lunar hotel, check out the Brains On podcast where we have a whole episode all about building stuff on the moon. Want to see our shows come to life? Head over to YouTube where we've got awesome animated Brains On episodes. Just search Brains On Universe on YouTube and subscribe.

If you have a question, we'd love to help you answer it. Drop us a line by going to brainson.org slash contact. See you next time and the next day and every weekday. Until then, um... Roses are red. Lilies are white. The moon reflects the bright solar light.