WEBVTT - How many moons does the Earth have? 0:00:08.520 --> 0:00:11.240 Hey, Kelly, do you ever wish that our night sky 0:00:11.560 --> 0:00:14.960 was I don't know, a little bit more dramatic, more dramatic. 0:00:15.360 --> 0:00:19.639 We've got a huge moon, planets, stars, and all of 0:00:19.680 --> 0:00:22.079 the Milky Way. You've got pretty high standards for the 0:00:22.160 --> 0:00:24.200 night sky. What did you have in mind? I don't know. 0:00:24.320 --> 0:00:26.960 Sometimes I think it's boring to have just that one 0:00:27.240 --> 0:00:30.080 huge moon. It seems like it might be more exciting 0:00:30.120 --> 0:00:33.080 to have lots of little moons up there. Okay, all right, 0:00:33.159 --> 0:00:36.440 that's true. It's kind of like having an only child. Yeah, 0:00:36.479 --> 0:00:39.720 and not just an only child, like a single mega child. 0:00:40.479 --> 0:00:44.000 You want drama. What's more dramatic than the Earth's mega 0:00:44.120 --> 0:00:46.800 child hovering above you in the sky. Yeah, I guess 0:00:46.800 --> 0:00:48.880 I wanted drama. But now I'm worried that the idea 0:00:48.880 --> 0:00:51.720 of a mega child is going to give me nightmares. Yeah, 0:00:51.760 --> 0:01:09.600 me too. I like my two little ones. Hi. I'm Daniel. 0:01:09.680 --> 0:01:12.240 I'm a particle physicist, and I'm very happy to have 0:01:12.319 --> 0:01:16.120 too normal sized children instead of one mega child. And 0:01:16.200 --> 0:01:18.920 I'm Kelly. I'm a parasitologist, and I also have two 0:01:18.959 --> 0:01:21.280 normal sized children, and that works well for me. You 0:01:21.360 --> 0:01:24.240 having considered the concept of like combining them together into 0:01:24.280 --> 0:01:27.080 one child unification of the children. You know, Zach likes 0:01:27.120 --> 0:01:29.720 to joke that they stack when he stacks them. They 0:01:29.760 --> 0:01:31.760 don't seem very happy about it, and so you know, 0:01:31.800 --> 0:01:34.080 I haven't thought too hard about trying to combine them. 0:01:34.080 --> 0:01:35.800 I don't think they'd be big fans of that. I'm 0:01:35.800 --> 0:01:38.320 pretty sure my kids wouldn't be into that either. Well, 0:01:38.360 --> 0:01:41.960 Welcome to the podcast Daniel and Jorge explain the universe 0:01:42.040 --> 0:01:44.720 and which we ask the hard questions of the universe. 0:01:44.760 --> 0:01:47.720 We talked about the crazy stuff that's out there deep 0:01:47.800 --> 0:01:50.000 in the cosmos, and we talked about the tiny little 0:01:50.040 --> 0:01:53.160 particles that are wriggling around inside my children, your children, 0:01:53.400 --> 0:01:56.960 and everybody's children. We try to explore the entire universe 0:01:57.000 --> 0:01:59.720 and explain all of it to you. Normally we have 0:01:59.800 --> 0:02:02.360 my friend and co host Jorge him here on the podcast, 0:02:02.480 --> 0:02:05.800 but he's unavailable today, so we have our wonderful, hilarious 0:02:05.840 --> 0:02:08.920 guest host, Kelly Weener Smith. Hello, I'm excited to be back. 0:02:09.000 --> 0:02:11.160 Thanks very much for joining us and for talking to 0:02:11.240 --> 0:02:14.880 us about crazy stuff in the universe. So on the podcast, 0:02:14.960 --> 0:02:18.480 we sometimes like to dig into stuff that's really complicated, 0:02:18.800 --> 0:02:21.280 like how does quantum field theory work, and what is 0:02:21.320 --> 0:02:23.680 the real charge of the electron? Or what is it 0:02:23.760 --> 0:02:26.760 like to go inside a black hole? These are deep 0:02:26.800 --> 0:02:29.160 and complicated questions about the universe that we try to 0:02:29.160 --> 0:02:32.160 take apart and explain to you. But sometimes we also 0:02:32.200 --> 0:02:35.440 like to dive into simpler seeming in questions, questions that 0:02:35.760 --> 0:02:38.320 might seem like they have an obvious answer but then 0:02:38.400 --> 0:02:41.640 have some interesting little wrinkles. It's good to have diversity, yeah, 0:02:41.639 --> 0:02:44.119 because questions are at the heart of science, and they're 0:02:44.160 --> 0:02:46.800 not just the questions that scientists ask when they're doing 0:02:46.840 --> 0:02:49.320 their research, but we're also interested in the questions that 0:02:49.440 --> 0:02:53.040 everybody asks. And sometimes the best questions are the questions 0:02:53.080 --> 0:02:56.960 that children ask, the most obvious questions which sometimes have 0:02:57.040 --> 0:02:59.359 a tricky answer. And I remember looking up at the 0:02:59.480 --> 0:03:02.840 night sky with my kids, who are now twelve and fourteen, 0:03:02.960 --> 0:03:07.520 but earlier asked very simple, basic, fun questions about the universe, 0:03:07.600 --> 0:03:11.160 like why do we only have one moon? Or do 0:03:11.480 --> 0:03:14.480 we only have one moon? Kelly, what kind of questions 0:03:14.480 --> 0:03:16.360 do your kids ask when they look at the night sky? 0:03:16.639 --> 0:03:18.959 I was just trying to think of a good example 0:03:19.120 --> 0:03:22.320 of Like, my daughter is seven, and she's always asking 0:03:22.320 --> 0:03:24.560 me questions that I don't know the answer to some 0:03:24.680 --> 0:03:27.560 of them super fundamental, which makes me think, how is 0:03:27.600 --> 0:03:30.120 it that I'm walking around not knowing the answer to 0:03:30.160 --> 0:03:32.560 all of these fundamental things, but yet I still managed 0:03:32.600 --> 0:03:35.440 to survive. But no good example is coming to mind 0:03:35.520 --> 0:03:37.480 right now. But we've got one of those apps on 0:03:37.480 --> 0:03:39.120 our phone where you can sort of point it at 0:03:39.200 --> 0:03:40.960 whatever in the night sky and it tells you what 0:03:41.000 --> 0:03:42.600 it is. And we spend a lot of time sitting 0:03:42.640 --> 0:03:44.880 on our car at night looking up at stuff, and 0:03:44.920 --> 0:03:46.840 it's a lot of fun. She asked lots of questions, 0:03:46.880 --> 0:03:48.800 but nothing's coming to mind right now that I did 0:03:48.800 --> 0:03:50.840 not know the answer to. What's your favorite question your 0:03:50.880 --> 0:03:52.960 kids have asked you? One of my favorite questions my 0:03:53.080 --> 0:03:56.080 kids have asked me are questions like where are we 0:03:56.200 --> 0:03:59.080 in the universe. You know, they're just getting used to 0:03:59.120 --> 0:04:01.440 the idea of like our houses in the neighborhood, and 0:04:01.480 --> 0:04:03.680 the neighborhood is in the city, and that city is 0:04:03.720 --> 0:04:06.480 in a state somewhere we have like a location and address, 0:04:07.000 --> 0:04:09.200 and so they wanted to know, like, where are we 0:04:09.320 --> 0:04:13.520 in the universe? What's our like universe address? And of course, 0:04:13.520 --> 0:04:16.800 you know, the hardcore physics answer is that every place 0:04:16.839 --> 0:04:19.480 in the universe is the same, and physics doesn't care 0:04:19.520 --> 0:04:22.680 about location and translationally and variant and stuff. But that 0:04:22.720 --> 0:04:25.760 answer is not very satisfying for a four year old. Yeah, 0:04:25.800 --> 0:04:27.400 that's why it's a bummer to have a physicist for 0:04:27.440 --> 0:04:31.920 a dad. But instead I try to describe to them, 0:04:31.960 --> 0:04:34.039 you know, what the galaxy looks like, and how the 0:04:34.040 --> 0:04:36.440 galaxy fits in with other galaxies, and what we know 0:04:36.520 --> 0:04:39.279 about sort of our cosmic neighborhood. And the thing I 0:04:39.360 --> 0:04:42.479 love about their questions is that they are both easy 0:04:42.640 --> 0:04:46.520 and hard. They're like easy to ask but sometimes hard 0:04:46.600 --> 0:04:49.360 to answer. And they're the obvious questions, as you said, 0:04:49.360 --> 0:04:51.760 that you don't always think about when you're walking around 0:04:51.760 --> 0:04:53.839 the world. But that's why I think that children really 0:04:53.880 --> 0:04:57.599 are sometimes the most natural scientists, because they don't just 0:04:57.720 --> 0:04:59.960 accept things as they are. They ask questions about the 0:05:00.000 --> 0:05:01.840 and say why is it this way or is it 0:05:01.880 --> 0:05:04.560 that way? After all? Totally, And what I love about 0:05:04.600 --> 0:05:06.960 Ada is that she'll tell me that I'm wrong. I 0:05:07.000 --> 0:05:09.360 wish I had that confidence. So you know, not only 0:05:09.400 --> 0:05:11.880 do they ask good questions, but they still have the 0:05:11.920 --> 0:05:14.560 confidence of children to be like, no, I don't think so. 0:05:14.760 --> 0:05:16.840 And so today in the podcast, we'll be talking about 0:05:16.839 --> 0:05:19.960 a question which seems to have an obvious answer. So 0:05:20.000 --> 0:05:27.919 on today's program will be answering the question how many 0:05:28.040 --> 0:05:31.359 moons does the Earth have? So, Kelly, tell me what 0:05:31.440 --> 0:05:32.719 you thought when you saw that we would be talking 0:05:32.720 --> 0:05:35.360 about this today. So you sent me a list of 0:05:35.360 --> 0:05:38.039 topics we could talk about, And when I read this one, 0:05:38.400 --> 0:05:42.120 I thought, well, the answer seems obvious. The answer is one. 0:05:42.680 --> 0:05:45.560 And if the answer seems obvious, then either Daniel needs 0:05:45.600 --> 0:05:48.560 to be fired because he's not asking good questions anymore, 0:05:49.160 --> 0:05:53.120 or there's something fundamental that I'm missing, and it's probably 0:05:53.160 --> 0:05:56.000 the second. And so I suggested that we talked about 0:05:56.000 --> 0:05:57.760 this one because I figured this was a question that 0:05:57.800 --> 0:06:00.360 would teach me something new. Awesome. This is a fun 0:06:00.480 --> 0:06:02.640 question to dig into. We get to hear about like 0:06:02.720 --> 0:06:05.360 what exactly is a moon, what counts as a moon, 0:06:05.720 --> 0:06:08.159 even a little bit about the etymology of the word 0:06:08.240 --> 0:06:10.760 moon and when it came into use, and what else 0:06:10.839 --> 0:06:13.440 is out there orbiting around the Earth and could you 0:06:13.560 --> 0:06:16.440 call it a moon? So, as usual, before I dug 0:06:16.480 --> 0:06:18.760 into this, I wanted to know what everybody else out 0:06:18.880 --> 0:06:21.320 there thought. Sometimes I used to walk around the campus 0:06:21.320 --> 0:06:24.240 if you see Irvine and ask students there these questions 0:06:24.279 --> 0:06:27.440 to see what the general level of knowledge was or confusion. 0:06:27.520 --> 0:06:30.359 These days, of course, because the pandemic, I'm sending emails 0:06:30.360 --> 0:06:34.159 out into the Internet asking listeners to speculate baselessly without 0:06:34.200 --> 0:06:37.479 the chance to do any research on these difficult physics questions. 0:06:37.600 --> 0:06:39.840 Did you actually stop students on the campus and ask 0:06:39.920 --> 0:06:42.200 them how many moons does they are? Have? No, I 0:06:42.200 --> 0:06:45.080 haven't because this question is too recent, But I wonder 0:06:45.160 --> 0:06:47.560 what they would say. I've noticed that our listeners tend 0:06:47.560 --> 0:06:50.200 to give better informed answers than the random you see 0:06:50.200 --> 0:06:53.440 Irvine student. Nothing against you see Irvine. Of course, our 0:06:53.480 --> 0:06:56.080 listeners may just be like a subset of the universe 0:06:56.080 --> 0:06:59.360 that's more interested in understanding the universe. But I hope 0:06:59.400 --> 0:07:01.279 one day to get back to campus and getting to 0:07:01.320 --> 0:07:03.560 ask the students those questions. It was fun to sort 0:07:03.560 --> 0:07:05.960 of see their faces when I asked them these questions. 0:07:06.040 --> 0:07:08.240 I bet you have a reputation as being one of 0:07:08.240 --> 0:07:11.400 the like super weird professors. Well, you know, I don't 0:07:11.520 --> 0:07:13.680 dress very fancy, so maybe they just think I'm some 0:07:13.840 --> 0:07:17.560 random homeless person asking them hard physical questions. Every college 0:07:17.600 --> 0:07:21.600 has homeless person or physics professor, it can be hard 0:07:21.640 --> 0:07:23.920 to tell the difference, physics professor, you can't tell the 0:07:23.960 --> 0:07:28.440 difference between Yeah, anyway, Thank you to everybody who volunteered 0:07:28.440 --> 0:07:30.720 to answer these questions. If you'd like to participate for 0:07:30.800 --> 0:07:33.440 a future episode of the podcast, please write to me 0:07:33.720 --> 0:07:36.960 two questions at Daniel and Jorge dot com. Here's what 0:07:37.040 --> 0:07:40.320 some of our listeners had to say. The obvious answer 0:07:40.360 --> 0:07:43.120 that pops into my head immediately would be one. So 0:07:43.200 --> 0:07:46.800 I'm pretty sure that answer is wrong. Well, we have 0:07:47.080 --> 0:07:53.520 just our celebrity moon, the moon, and I don't know, 0:07:54.040 --> 0:07:59.080 maybe we might have caught up some small objects there, 0:08:00.160 --> 0:08:05.800 probably a Deslo car elon musk scent, who knows. I 0:08:05.840 --> 0:08:10.280 don't know exactly. I'm one sure that the Earth has 0:08:10.360 --> 0:08:14.640 two moons, the classic moon that we see in the 0:08:14.720 --> 0:08:18.240 sky and Keith Moon. I would say the Earth has 0:08:18.320 --> 0:08:21.040 one moon. I don't know if you would consider satellites 0:08:21.120 --> 0:08:23.320 or a space station a moon because the orbit the Earth, 0:08:24.800 --> 0:08:27.280 but I would probably just consider one moon. Well, I 0:08:27.320 --> 0:08:32.280 guess this depends on your definition of moon the natural moons. 0:08:32.360 --> 0:08:36.199 It has the one large natural moon, and I believe 0:08:36.280 --> 0:08:39.440 they've discovered a couple of asteroids that have been captured 0:08:39.720 --> 0:08:44.480 in loose enough for bits that they're probably temporary. If 0:08:44.480 --> 0:08:49.319 you're going to call any artificial uh satellite a moon, 0:08:50.760 --> 0:08:54.400 which they've been called artificial moons, then that number goes 0:08:54.440 --> 0:08:58.600 into the millions, depending on how small a particle you 0:08:58.640 --> 0:09:03.080 want to count. There's nuts and bolts and pieces of 0:09:03.200 --> 0:09:09.200 rocket and larger things that satellites, fragments of satellites that 0:09:09.240 --> 0:09:13.360 have collided with each other, so uh, a whole lot 0:09:13.440 --> 0:09:15.480 of them, all right, Kelly, So what do you think 0:09:15.480 --> 0:09:18.160 about our listeners responses here? I thought there were some 0:09:18.280 --> 0:09:21.640 very insightful responses, you know. One of them was essentially 0:09:21.640 --> 0:09:25.600 asking questions about maybe how do we define moons. I 0:09:25.640 --> 0:09:28.760 thought somebody had a clever thought that the Tesla car 0:09:28.960 --> 0:09:31.360 might now be sort of orbiting, although I think of 0:09:31.400 --> 0:09:35.479 the Tesla car was shot Mars word instead of moonword. 0:09:35.640 --> 0:09:37.400 But it was clear that people sort of thought through 0:09:37.440 --> 0:09:39.680 their answers, and yeah, they had some clever answers. What 0:09:39.720 --> 0:09:42.080 do you think? Yeah, I was impressed as well. In 0:09:42.120 --> 0:09:43.720 the end, of course, it's going to come down to 0:09:43.760 --> 0:09:45.679 the definition. I hope that we end up with the 0:09:45.720 --> 0:09:48.800 definition of moon that doesn't allow Elon Musk to have 0:09:48.960 --> 0:09:52.520 created his own personal moon. That would seems sort of unsatisfying. 0:09:52.640 --> 0:09:55.000 That would be too much power for one person. The 0:09:55.080 --> 0:09:59.000 dude's already a billionaire and owns three like really valuable 0:09:59.000 --> 0:10:02.480 companies like it, doesn't need to create astronomical objects on 0:10:02.520 --> 0:10:04.560 top of all of it. Although he wants to create 0:10:04.640 --> 0:10:07.559 a Mars colony, which is maybe even more powerful than 0:10:08.000 --> 0:10:10.240 creating a moon. So I guess we'll have to see 0:10:10.240 --> 0:10:11.800 what the future holds. Do you think that's because he 0:10:11.840 --> 0:10:14.440 wants to be dictator of Mars? I like joking about 0:10:14.480 --> 0:10:19.559 that with Zack. Yes, he claims he wants a representative 0:10:19.640 --> 0:10:22.959 not a direct democracy, So we'll see what happens when 0:10:22.960 --> 0:10:24.720 the time comes. Well, if he gets to pick who 0:10:24.800 --> 0:10:26.400 goes to Mars, and they're probably going to elect him 0:10:26.440 --> 0:10:29.160 president anyway. But let's get back to the topic. We're 0:10:29.160 --> 0:10:31.920 not talking about Elon Musk's plan to colonize Mars. We're 0:10:31.920 --> 0:10:34.600 talking about moons and how many moons the Earth has 0:10:34.760 --> 0:10:38.440 and what exactly is a moon? So let's dig into 0:10:38.480 --> 0:10:42.560 that first and talk about what qualifies as a moon. So, 0:10:42.640 --> 0:10:45.040 without doing any research, Kelly, what would you use to 0:10:45.120 --> 0:10:47.960 define a moon? So I would have guessed that a 0:10:48.000 --> 0:10:53.240 moon is a big thing that isn't bigger than the 0:10:53.280 --> 0:10:56.120 planet that it orbits. So a big thing that orbits 0:10:56.160 --> 0:10:59.480 around a planet, and it has to be big, but 0:10:59.520 --> 0:11:02.439 it can't be bigger than the thing that it's orbiting around. 0:11:02.840 --> 0:11:05.280 That's how I would have defined it. But but probably 0:11:05.320 --> 0:11:08.360 that's wrong. And then your definition would it have to 0:11:08.360 --> 0:11:10.440 be natural or could be manned? Me that? Could we 0:11:10.480 --> 0:11:14.680 build an artificial moon? Oh h no, No, I've always 0:11:14.679 --> 0:11:18.199 thought of it as being natural. Yeah, what about you? Well, 0:11:18.200 --> 0:11:20.120 I really wasn't sure because it seems like in lots 0:11:20.160 --> 0:11:23.080 of directions there are arbitrary distinctions you have to make. 0:11:23.240 --> 0:11:25.680 And that's the problem often in astronomy is that the 0:11:25.720 --> 0:11:29.160 categories between things get blurred, and you always find something 0:11:29.280 --> 0:11:31.840 right on the edge between the different categories, and in 0:11:31.880 --> 0:11:33.240 the end, you know, we're just we're looking at the 0:11:33.280 --> 0:11:35.800 universe and we're trying to categorize it to understand is 0:11:35.800 --> 0:11:37.720 that we can talk about it together. Doesn't mean that 0:11:37.760 --> 0:11:41.360 those categories actually reflect something deep and true about the universe. 0:11:41.360 --> 0:11:44.640 There's sometimes just the words we've used to describe stuff, 0:11:44.960 --> 0:11:46.760 and so as we see more stuff out there in 0:11:46.760 --> 0:11:49.439 the universe, we're gonna find things that break those categories. 0:11:49.520 --> 0:11:51.400 But the definition that I found for moon is that 0:11:51.440 --> 0:11:54.480 it has to be a quote natural body, right, So 0:11:54.520 --> 0:11:57.520 it needs to be a natural body that's orbiting a planet. 0:11:57.840 --> 0:12:00.440 And to me already this is problem that like a 0:12:00.520 --> 0:12:03.840 natural body means not like a human made satellite. So 0:12:03.960 --> 0:12:07.079 we built a death Star for example, Officially that wouldn't 0:12:07.160 --> 0:12:12.400 qualify as a moon. But what if we just like 0:12:12.800 --> 0:12:15.400 you know, pulled out a huge chunk of Earth and 0:12:15.520 --> 0:12:18.040 threw it out into space and then it went into 0:12:18.160 --> 0:12:21.120 orbit around the Earth. Is that a natural body? It's 0:12:21.160 --> 0:12:24.360 like made of rock, right, It's essentially the same process 0:12:24.400 --> 0:12:27.360 that created our moon as we understand it. But I 0:12:27.360 --> 0:12:30.080 think according to this definition, it wouldn't be a moon 0:12:30.280 --> 0:12:32.280 because you know, it would have been like as the 0:12:32.320 --> 0:12:34.920 result of a human process. It really does seem like 0:12:34.960 --> 0:12:36.360 if you just took a chunk of earth and you 0:12:36.480 --> 0:12:39.320 put it up there, it should count. But I suppose 0:12:39.360 --> 0:12:42.240 satellites are just chunks of Earth that we've we've done 0:12:42.240 --> 0:12:45.600 things too, that we send up into space, and so 0:12:46.080 --> 0:12:49.079 maybe it shouldn't count. Yeah, exactly, That's where I was going. 0:12:49.160 --> 0:12:52.040 What is a satellite other than like an ultra refined 0:12:52.160 --> 0:12:55.120 piece of Earth that you've somehow, you know, manipulated into 0:12:55.160 --> 0:12:58.120 a complex technological object. But in the end, it's a 0:12:58.120 --> 0:13:00.920 piece of the Earth that we've launched into space. And 0:13:00.960 --> 0:13:02.760 you know, for those of you who don't know the 0:13:02.880 --> 0:13:05.959 history of our moon, we think that our moon is 0:13:06.000 --> 0:13:09.040 basically a big chunk of Earth that was vaulted out 0:13:09.120 --> 0:13:12.280 into space when another proto planet hit Earth when it 0:13:12.360 --> 0:13:15.240 was very very young, and this collision led to this 0:13:15.480 --> 0:13:18.319 enormous blab of stuff getting tossed out there, which eventually 0:13:18.360 --> 0:13:21.800 coalesced into the Moon. And when we studied the surface 0:13:21.840 --> 0:13:24.400 of the Moon, we found elements of it which look 0:13:24.480 --> 0:13:27.040 exactly the same as elements of the surface of the Earth, 0:13:27.040 --> 0:13:28.800 which suggests that they really do have sort of a 0:13:28.880 --> 0:13:31.840 common origin. So this definition of a moon being a 0:13:31.960 --> 0:13:35.640 natural body not a human made object is a little tricky, 0:13:35.760 --> 0:13:37.640 and I don't think the definition there is very clear. 0:13:37.800 --> 0:13:41.640 Can I ask a sort of tangential question, of course, So, well, 0:13:41.720 --> 0:13:43.880 Zach and I were reading about the Moon. We came 0:13:43.920 --> 0:13:47.160 across this fact that the Moon is sort of carbon poor, 0:13:47.320 --> 0:13:48.960 like maybe there's some carbon up there, but you're gonna 0:13:48.960 --> 0:13:50.679 have trouble growing plants and stuff because there's not a 0:13:50.720 --> 0:13:53.559 lot of carbon. If the Moon is just a chunk 0:13:53.600 --> 0:13:57.640 of Earth that got expelled, why do we have so 0:13:57.720 --> 0:13:59.320 much carbon and they have so little. Is that the 0:13:59.360 --> 0:14:02.320 result of natal processes that happened after the Moon got 0:14:02.360 --> 0:14:05.720 cut off partly, Yeah, Mostly the Earth and the Moon 0:14:05.800 --> 0:14:09.040 are made up of very similar stuff. It's mostly oxygen 0:14:09.160 --> 0:14:12.520 and silicon and calcium and iron and that kind of stuff. 0:14:12.559 --> 0:14:15.440 That's because we think that the Moon and the Earth 0:14:15.480 --> 0:14:18.360 are made up of the remnants of a huge collision 0:14:18.480 --> 0:14:21.840 between the proto Earth and a Mars sized planet, like 0:14:22.120 --> 0:14:25.480 fifty million years after the Solar system formed, and the 0:14:25.600 --> 0:14:29.440 remnants of that huge collision coalesced into the Earth and 0:14:29.520 --> 0:14:32.000 into the Moon. But you're right that there is very 0:14:32.080 --> 0:14:34.480 little carbon on the Moon, but there is carbon on 0:14:34.520 --> 0:14:38.560 the Earth's surface, and we're not sure why. One theory 0:14:38.680 --> 0:14:42.200 is that carbon tends to form very volatile compounds, things 0:14:42.240 --> 0:14:44.160 that would end up in an atmosphere if the Moon 0:14:44.240 --> 0:14:46.800 could keep one. So the Earth hangs onto some of 0:14:46.840 --> 0:14:49.400 these things, some of this carbon, because it's big enough 0:14:49.440 --> 0:14:51.880 to keep hold of its atmosphere it has more gravity, 0:14:52.040 --> 0:14:54.800 But the Moon can't. Anything like an atmosphere on the 0:14:54.800 --> 0:14:58.200 Moon just boils away. Interesting okay, thanks. So the definition 0:14:58.240 --> 0:14:59.960 of a moon is that needs to be a natural 0:15:00.000 --> 0:15:03.080 a body in orbit around a planet, and you said 0:15:03.120 --> 0:15:06.160 that it needs to be big. Officially, technically there's no 0:15:06.520 --> 0:15:10.440 minimum size to a moon. A moon could be like huge, 0:15:10.560 --> 0:15:13.840 like our moon, or you know, according to astronomers, it's 0:15:13.880 --> 0:15:16.720 okay to have a moon that's like a kilometer in size. 0:15:16.800 --> 0:15:19.320 I find that very unsatisfying. Like to me, a moon 0:15:19.560 --> 0:15:21.640 is something that you should be able to, like put 0:15:21.680 --> 0:15:24.160 a settlement on one day, and you can't really do 0:15:24.240 --> 0:15:28.920 that with a one kilometer sized quote unquote moon. I 0:15:28.920 --> 0:15:31.280 don't know. I don't want to buy that, but apparently 0:15:31.280 --> 0:15:32.720 it's part of the definition. It would be like the 0:15:32.720 --> 0:15:35.640 little prints right walking around this tiny little planet. But 0:15:35.720 --> 0:15:38.920 I think that comes from our experience, right, just because 0:15:38.960 --> 0:15:41.080 we have this one big moon, we tend to think 0:15:41.280 --> 0:15:43.520 that's what you gotta have in a moon. But as 0:15:43.560 --> 0:15:45.640 well talk about later, so many planets in the Solar 0:15:45.680 --> 0:15:47.840 System don't have a huge moon, to have a lot 0:15:47.840 --> 0:15:51.000 of smaller moons, And so part of the joy of 0:15:51.000 --> 0:15:54.320 astronomy and and of exploring the universe is discovering that 0:15:54.440 --> 0:15:57.000 our corner of the universe is weird, is unusual, is 0:15:57.040 --> 0:15:59.320 not representative, and we've got to sort of like stretch 0:15:59.360 --> 0:16:01.720 our mind then get used to a different way of 0:16:01.720 --> 0:16:04.080 thinking about what a moon is. Yeah, it is really 0:16:04.080 --> 0:16:06.960 hard to wrap your mind around just how different it is. 0:16:07.000 --> 0:16:08.880 And yeah, I'm very earth centric. I guess I would 0:16:08.880 --> 0:16:11.360 like moons to all sort of fits in a nice 0:16:11.400 --> 0:16:13.920 little mold that matches the moon that I have, and 0:16:13.960 --> 0:16:15.840 you touch it on really all the important issues. I 0:16:15.840 --> 0:16:17.800 think that was really tremendous. The other thing you mentioned 0:16:18.040 --> 0:16:20.200 is that it shouldn't be bigger than the planet, right, 0:16:20.760 --> 0:16:23.360 And in the definition of a moon, officially, the upper 0:16:23.400 --> 0:16:26.000 limit on the size of a moon is pretty vague, 0:16:26.440 --> 0:16:29.280 Like what happens when the moon approaches the size of 0:16:29.280 --> 0:16:31.600 the planet. Then you might ask, like, well, which one 0:16:31.640 --> 0:16:33.520 is the planet and which one is the moon? Right? 0:16:33.640 --> 0:16:36.960 Or if they're exactly equal size, could you consider them 0:16:37.000 --> 0:16:39.760 to be like a binary planet system? So where does 0:16:40.040 --> 0:16:44.560 our moon fall relative? And they'll like Earth to Moon 0:16:44.800 --> 0:16:47.880 ratio side, Like, is our moon big for a moon? 0:16:48.120 --> 0:16:50.080 Is it the biggest relative to the size of the 0:16:50.120 --> 0:16:52.880 planet it orbits is? So is our moon weird relative 0:16:52.920 --> 0:16:55.280 to the other moons? Our moon is very weird. Our 0:16:55.320 --> 0:16:58.920 moon is basically that megachild. The diameter of the Moon 0:16:59.400 --> 0:17:01.880 is more than a quarter of the diameter of the Earth, 0:17:02.360 --> 0:17:05.119 and that's the biggest moon to planet ratio in the 0:17:05.119 --> 0:17:08.080 Solar System by like a factor of five. There's no 0:17:08.240 --> 0:17:10.480 other planet out there that has such a big moon 0:17:10.600 --> 0:17:13.920 relative to the planet. Like there are moons of Jupiter 0:17:14.240 --> 0:17:16.240 that are roughly the same size as our moon, but 0:17:16.280 --> 0:17:19.040 of course Jupiter is huge, and so relative to the 0:17:19.040 --> 0:17:21.840 size of Jupiter, those moons are very very small, So 0:17:21.880 --> 0:17:24.480 we have a really weird big moon. You know, it's 0:17:24.520 --> 0:17:26.800 kind of amazing that we've managed to figure out anything, 0:17:26.880 --> 0:17:29.159 which is sort of a phrase that, if I'm remembering correctly, 0:17:29.200 --> 0:17:31.600 I've said in almost every single one of these episodes 0:17:31.640 --> 0:17:33.760 we've done together. But it seems like, you know, our 0:17:33.800 --> 0:17:36.479 Solar System is so weird, and our planet and the 0:17:36.480 --> 0:17:39.159 moon is so weird. It gives us such a weird 0:17:39.240 --> 0:17:41.399 frame of reference. But I know, it's exciting that we 0:17:41.440 --> 0:17:44.120 can still figure stuff out. Yeah, and it's a real 0:17:44.280 --> 0:17:47.920 journey to peel away these preconceptions and understand that things 0:17:47.920 --> 0:17:51.280 we thought were fundamental, things we thought we're obvious or universal, 0:17:51.600 --> 0:17:54.200 are really just unusual. You know. It's just like when 0:17:54.240 --> 0:17:56.760 you go traveling and you discover like, oh, not everybody 0:17:56.880 --> 0:17:59.320 drinks coffee for breakfast. You know, it turns out there 0:17:59.320 --> 0:18:01.600 are other ways to live, and that's the joy of 0:18:01.640 --> 0:18:04.440 exploring the universe, you know, discovering the tea is also 0:18:04.480 --> 0:18:08.159 acceptable at breakfast times. No, no, no, no, no, no, 0:18:08.840 --> 0:18:11.240 that's just wrong. One fact that I really liked while 0:18:11.280 --> 0:18:13.200 I was reading through here was that those like one 0:18:13.280 --> 0:18:17.880 kilometer size moons are sometimes called moonlits. And I thought 0:18:17.880 --> 0:18:19.920 that was super cute. So I asked my seven year 0:18:19.960 --> 0:18:21.840 old today. I was like, how many moons does the 0:18:21.840 --> 0:18:25.479 Earth have? So she, being a very clever kid, was like, well, 0:18:25.520 --> 0:18:27.399 I thought it was one, but you're asking me this, 0:18:27.560 --> 0:18:30.720 so what does that mean? And and so I told 0:18:30.720 --> 0:18:32.320 her like, well, you know you can have these little 0:18:32.359 --> 0:18:35.000 things called moonlits. And she said, well, what does that mean? 0:18:35.080 --> 0:18:37.160 And so I tried to explain that let's means little 0:18:37.200 --> 0:18:39.639 things and she was like, well, when else does it 0:18:39.680 --> 0:18:42.840 mean that? And I had a like, uh, you know, 0:18:42.880 --> 0:18:44.720 like a moment of not being able to figure it out, 0:18:44.720 --> 0:18:46.439 but I came up with piglets and outlets, and I 0:18:46.480 --> 0:18:48.480 was very proud of myself. So anyway, that was a 0:18:48.520 --> 0:18:50.680 fun moment with the seven year old today. Yeah, I 0:18:50.720 --> 0:18:53.439 love those little endings lits and like, it's just like 0:18:53.480 --> 0:18:57.280 the diminutive in Spanish, you know, eto or eno or 0:18:57.320 --> 0:18:59.640 these kind of things in romance languages. So I'm glad 0:18:59.640 --> 0:19:01.440 that we have those in English. Also, you could really 0:19:01.480 --> 0:19:04.000 stick them on anything, you know, like I'm not having dessert, 0:19:04.000 --> 0:19:08.840 I'm having dessert lits. It makes everything cuter, it really does. 0:19:09.280 --> 0:19:11.159 So where are we with the moons? Moons have to 0:19:11.200 --> 0:19:14.520 be a natural body orbiting a planet. No minimum size. 0:19:14.760 --> 0:19:17.679 The oppera limit is kind of vague. One thing I 0:19:17.760 --> 0:19:20.760 read suggested that you could effectively describe an upper limit 0:19:20.840 --> 0:19:24.400 on the moon by requiring that the center of mass 0:19:24.440 --> 0:19:28.239 of the planet and moon together should be inside the 0:19:28.280 --> 0:19:30.960 diameter of the planet. Right, So the center of mass 0:19:30.960 --> 0:19:33.719 of two objects is sort of like the weighted average 0:19:34.040 --> 0:19:36.320 of all of their stuff. If you've got more stuff 0:19:36.320 --> 0:19:38.159 in the planet than in the moon, it's going to 0:19:38.200 --> 0:19:41.040 be closer to the planet mathematically and physically. It's actually 0:19:41.160 --> 0:19:43.840 the location that the two things are orbiting. Right. We 0:19:43.960 --> 0:19:46.600 say that the Moon, for example, orbits the Earth, but 0:19:46.680 --> 0:19:49.840 actually the two things are orbiting each other, or more precisely, 0:19:50.040 --> 0:19:53.480 they're both orbiting the center of mass of the two things. 0:19:53.720 --> 0:19:55.680 And if you have two things that are equal mass, 0:19:55.800 --> 0:19:58.280 then their center of masses right between them. If one 0:19:58.280 --> 0:20:00.720