NASA Scientist: Would you like to be an astronaut? Boy: Yeah, maybe! NASA Scientist: Say, aren’t you one of the treehouse detectives? Boy: Yes, I am, and you must be from NASA Langley. NASA Scientist: Yes, I am, and I understand from your email that you want to know more about the moon. Boy: Yes. I was looking at the moon the other night, and I was wondering why it had different shapes. NASA Scientist: The different shapes are called the phases of the moon. Come over here and I’ll show you what I mean. Boy: What do you do with the lamp? NASA Scientist: The lamp represents the sun. Think of this ball as the moon, and you’re the Earth. Boy: OK NASA Scientist: Now hold the ball in front of you, towards the sun. What do you see there? Boy: The side that I’m looking at is dark. NASA Scientist: That’s right. That’s called the new moon phase. Now turn to the left a quarter turn and keep holding the moon in front of you and tell me what you see. Boy: Now half the side that I’m facing is lit. NASA Scientist: That’s called first quarter. Keep going. Boy: Now the whole thing is light. This must be a full moon. NASA Scientist: Keep going… Boy: Now only half is lit but it’s the other side. NASA Scientist: That’s called the moon’s third quarter phase. Boy: I get it, so the phases of the moon are created when the moon revolves around the Earth. NASA Scientist: The same side of the moon is always facing the Earth, and as it revolves around the Earth, different portions of the surface are illuminated by the Sun. Those are the lunar phases. Boy: Why do we only see one side of the moon? NASA Scientist: The moon rotates on its axis once every 27.3 days. It turns out that it’s also 27.3 days that it takes to revolve around the Earth. That’s why the same side of moon is always facing the Earth. Boy: How old is the moon? NASA Scientist: The moon is a lot older than you and me. About four and half billion years, roughly the age of the Earth. That’s where the similarities end. Boy: What do you mean? NASA Scientist: Well, there’s no atmosphere on the moon and the gravity is much less—it’s only about one-sixth of the gravity of the Earth on the surface of the moon. Boy: So if I weigh ninety pounds on the Earth, then I would weigh fifteen pounds on the moon. NASA Scientist: That’s right. The surface of the moon is very different, too. Boy: So what are those big circles that I see when I look at the moon? NASA Scientist: Those circles are craters, from the meteors and the asteroids that have impacted on the moon over the years. There’s no water or weather erosion to help get rid of them, so they’re all still there. Boy: So what is the surface like? NASA Scientist: The surface is generally gray in color, and sandy. It feels very much like this concoction. Boy: Feels like dust. NASA Scientist: You’re right. There was a real concern early in the moon program that it might be like quicksand and the astronauts could sink in it, but of course that did not happen. Boy: Good thing they didn’t. Does the moon affect the Earth at all? NASA Scientist: Oh yes. The moon affects the tides, and if we were on the beach…how did that happen?! I don’t even want to ask! The moon’s gravitational pull depends on the distance. It’s greater on the oceans, closest to the moon, than on the center of the Earth. This tends to pull the oceans into a big bulge. Boy: Anything else? NASA Scientist: Actually, the moon is increasing the length of our day by .0016 seconds every century. Boy: We can measure that? Wow, I’m impressed! How does it lengthen the day? NASA Scientist: The Earth’s tide act like a brake, gradually reducing the speed of the Earth’s rotation. Boy: That’s so interesting. Thanks! You’ve given me a lot of useful information! NASA Scientist: Now I wonder how we’re going to get back to the museum!