How much does the moon weigh? (1)
Jane Lindholm] This is But Why: A Podcast for Curious Kids produced at Vermont Public Radio. I'm Jane Lindholm. On this show we take questions from interesting kids like you and we dig up the answers. Today we're talking about something we all see at night, but only a very few very lucky people have ever been able to visit. [Neil Armstrong] That's one small step for man; one giant leap for mankind. [Jane] Today we're going to learn all about the moon. That recording was astronaut Neil Armstrong. You may have heard of him. On July 20th, 1969 he and fellow astronaut Buzz Aldrin were the first two people in the history of the world to walk on the moon...[Jack King] ...twelve, eleven, ten, nine. Ignition sequence... [Jane] ...Their mission was named Apollo Eleven...[Jack]...four, three, two, one, zero. All engine running. Lift off! We have a lift off! 32 minutes past the hour, lift off on Apollo Eleven. [Jane] The goal of the mission was to land a lunar module nicknamed “The Eagle” on the moon. [Neil] Tranquility base here. The Eagle has landed.
[Charlie Duke]..Roger, Tranquility. We copy you on the ground. You got a bunch of guysabout to turn blue. We're breathing again. Thanks alot. [Jane] After their spaceship landed on the moon they put on their spacewalking suits and opened the door of their ship. And then they took those first very important steps. But, they weren't just going to the moon to see if they could or for the sheer adventure of it.
The astronauts and NASA, the U.S. space program, were doing experiments and collecting samples of wind and lunar rocks. Lunar means “of the moon.” It's from the Latin word that means moon. And if you speak French, or Spanish, or Italian you'll know that word loon or Luna. Anyway, the astronauts were also collecting information about the internal structure of the moon and measuring its exact distance from earth. This year, in just a couple of months, it will be the 50th anniversary of the Apollo 11 mission. Now, other moonwalks followed in missions that came later, and today, most missions to space don't include a trip to the moon. But, the moon is still fascinating to many of us here on Earth. Maybe that's because it's the biggest and brightest object in our night sky. It's easy to stare at the moon and imagine what it's like up there or wonder what it even is and how it moves through the sky. The moon is a satellite. A satellite is something that moves or rotates around a planet, the earth in this case. The moon is two-hundred thirty-nine thousand miles away. That's far, but it's way closer than any of the other stars or planets you can see in the night sky. That's why the moon looks so big compared to other celestial objects even though the stars are actually much bigger. We've gotten a lot of moon questions from you over the last couple of years. So, as we approach the
anniversary of that very first moon landing, we thought it might be neat to get some answers from one of our favorite But Why friends.
[John O'Meara] Hi, my name is John O'Meara and I am the chief scientist of the W.M. Keck Observatory on the summit of Mauna Kea on the Big Island of Hawaii.
[Jane] We've talked to John O'Meara before about all kinds of astronomical things And he just took this job in Hawaii with the Keck Observatory, where astronomers and astrophysicists do research with two very large, very powerful telescopes. Our first question for John about the moon comes from Sagan.
[Sagan] I'm four and a half years old and my question is, why is there only one moon?
[John] This is a really cool question, Sagan. I wish I knew the answer to it, too. And I think it's probably because of how the solar system formed early on. Very early on in the history of the solar system, about four and a half billion years ago, all the stuff that was going to form into the planets started to collapse and form things like planets, but we called them protoplanets. They were smaller than the Earth is today. And those things, due to their gravitational pull on their surroundings, would start to get bigger as the smaller rocks would fall onto the bigger protoplanet. And eventually those things formed the rocky planets close to the sun. Farther out, it was too cold and so it was ices that would start to glom together, and then gas would fall onto them, and those would create the gas giants like Jupiter and Saturn, Uranus and Neptune. And those planets have lots and lots of moons. Some of them have over 60 moons. But back to your question, why does the earth have only one moon? Well, it turns out that the earth's moon is likely the result of something almost the size of Mars hitting the Earth many billions of years ago. And then those two pieces calmed down, cooled down and became the earth and the moon. And as a side effect, this is why we have the seasons. Because when this thing smacked into the earth many billion years ago, it knocked it slightly over from being straight up relative to where it's spinning and that's why we have seasons: because in some parts of the year we're tilted away from the sun and some parts of the year were tilted towards the sun.
[Anisa] Hi, my name is Anisa and I am eight years old and I live in Clarksburg, Maryland. And my question is, how much does the moon weigh?
[John] How much does the moon weigh? Well, it weighs a lot! In fact, it weighs one with twenty-three zeros after it pounds. And that's just such a big number that it really almost has no meaning to me. Instead, I like to think about how much does the moon weigh compared to something like the Earth? And, it turns out that the moon is about one percent the mass of the earth. And that is a lot!
[Jane] Here's a question about the way the moon looks.
[Mika] My name's Mika. I'm five and a half. I'm from Portland. Oregon. My question is,
why does the moon have holes?
[John] Hi, Mika. Good question. The moon has craters all over it, craters of different sizes and shapes. Some craters are a little bit younger than others. Some craters are very, very old, billions of years old. And the reason why the moon has all these craters is that over billions of years, hundreds of thousands of objects have smacked into the moon, like asteroids, comets, smaller bodies, things like that. And they keep pummeling the moon and hitting it and creating these craters. And sometimes the craters are very, very big
because it's a very big object hitting it. And sometimes earlier on in the history of the moon, a big object would hit it and it would cause lava to flow out through the hole that it punctured in there. And that's why parts of the moon look darker than others. It's all because these things keep smacking into the moon now.
[Jane] Now, Argen wanted to know about the color of the moon.
[Argin] I'm 6 years old and l live in Canada. My question is, why is the moon white?
[John] So the moon appears to have lots of different colors. But when you get up really close to the surface of the moon, it's mostly sort of this dull grayish black. But that's not what we see from the earth. From the earth we often times see that parts of the moon are brighter than the others. And that's partly because the rocks are different colors in some of the regions where it's darker, that's because lava used to flow on top of there after a big impact. But most of the differences in colors are because of the way that the sunlight is bouncing off of the moon. And that makes some regions much brighter than others. In fact, that's what's responsible for the phases of the moon.
[Jane] When John O'Meara says the phases of the moon, he's talking about the shape of the moon and how it changes over the course of about 28 days, a full cycle. The moon is always a sphere, a ball, but it doesn't always look like that. Sometimes you look up at the moon and it looks like a banana or a crescent. Sometimes it looks like half a circle and sometimes it's a bright full circle, a full moon. But why?
[Satchel] Hi, my name is Satchel. I live in Mobile, Alabama. I'm five years. And my question is, why does the moon change its shape: circle, half, banana half?
[Sawyer] My name is Sawyer. I am eight years old. I live in Sherman, Texas. My question is, why does the moon change color and get smaller in the night sky?
[Lauren] Hi, my name is Lauren and I'm six years old and I live in Washington, New Hampshire and my question is why isn't the moon always round?
[John] Again, the reason for this is because we actually see the moon in reflected
sunlight. Sunlight bounces off of the surface of the moon and into our eyes. The moon itself doesn't make its own light. And so depending on where we are on the earth and where the moon is in the sky, you'll see different amounts of light reflected off of it. Sometimes the moon is in between us and the sun, and so we don't see any sunlight reflected off of the surface. And that's what we call a new moon. On the other hand, if the moon is on the opposite side of the earth from the sun, then we see the entire surface that's facing us off of the moon in reflected sunlight. And that's what we call a full moon. So the moon itself isn't changing its shape. It's just reflecting different amounts of light into our eyes.
[Jane] Later in this episode...
Why does the moon always look like it's following us in the car always? [Jane] And why can you sometimes see it during the day?
This is But Why: A Podcast for Curious Kids. I'm Jane Lindholm. Today, we're talking all about the moon with John O'Meara, chief scientist at the Keck Observatory. We've talked
a little bit about how the moon doesn't actually change shape, but often looks very different to us in the sky, depending on where it is in its phase: How much sunlight we can actually see shining onto the surface of the moon? When the earth is in between the sun and the moon only some of the surface of the moon gets that sunlight shining onto it, so parts of the moon appeared dark, and it makes the moon look like a banana or a crescent. That only happens because the earth and the moon are both moving all the time.
[Nina] Hi, my name is Nina. I am five years old. I live in Illinois. And my question is, how does the moon move?
[Rebecca] Hi, my name is Rebecca. I'm 4 years old. My question is, how does the moon stay in place?
[Jane] This is complicated and you'll probably learn a lot more about it when you get into high school physics. But let me give you a very brief overview. Remember how John O'Meara said that the best theory scientists have for how the moon was formed is that it came from a collision, a crash between the earth and an object about half its size, about the size of Mars. Well, when that crash happened, the material that was thrown away from the earth was traveling very fast. It all joined together to form the moon. And the force known as gravity kept it from just continuing out into space. The moon basically got trapped by the Earth's gravity. The force of gravity pulls the moon towards the earth, and then the moon moves around the earth. It can never get away from the earth because of gravity, and it doesn't become closer to the earth because it's still trying to move away. The moon, by the way, also exerts a force on the earth, and it takes the moon a little less than 28 days to go all the way around the earth and start again. That's one full cycle of the moon. Now, speaking of gravity...