The Great Attractor & Saturn’s Rings: Unravelling Cosmic Questions | Space Nuts: Astronomy...

[00:00:00] [SPEAKER_04] Andrew Dunkley, The Great Attractor G'day. Thanks for joining us again on Space Nuts. My name is Andrew Dunkley, your host. I hope you're well. Coming up in a Q&A episode, we're going to be looking at the sun and the moon. A little bit of confusion going on there. It's all about the angles, I think. We're also going to see if we can tackle a question about the Great Attractor. Is it John Deere or Massey Ferguson? Ooh, I don't know.

[00:00:27] [SPEAKER_04] We're also... We've had this question before, but I think this is sort of a follow-up question on redefining a moon. What defines a moon and what do you take into account to define a moon? And finally, an interesting question from someone who has a friend who's writing a graphic novel, which is also science fiction, and it's set on a planet that's got rings, and she's wondering about the rings.

[00:00:53] [SPEAKER_04] What do you see when you're standing on the planet looking up at them, and how do they act, and what do they do, and can you put it on your finger, and is it worth anything? That's all coming up on this edition of Space Nuts.

[00:01:05] [SPEAKER_05] 15 seconds. Guidance is internal. 10, 9. Ignition sequence start. Space Nuts. 5, 4, 3, 2... 1, 2, 3, 4, 5, 5, 4, 3, 2, 1. Space Nuts. Astronauts report it feels good.

[00:01:21] [SPEAKER_04] And joining us again as he funders away on his keyboard to try and answer all these questions, because he's so well prepared, is Professor Fred Watson.

[00:01:29] [SPEAKER_06] Astronomer-alard. Hello, Fred. I'm just writing the email I should have sent before we started. Yes. Ah, dear.

[00:01:36] [SPEAKER_04] I can wait. No, it's okay. It's fine. It's only 500 words. Shall we get straight into it and see if we can solve some of these puzzles from people? I think we should do, yeah. Justin has sent in a question. I don't know where Justin's from. Probably from his house. I was at work the other morning and the sun and the moon were both in the eastern sky, yet it was a crescent moon, the same moon as the night before.

[00:02:06] [SPEAKER_04] How is this possible? That's a good question, because I've often wondered the same thing. I'll look up and go, hang on a minute. The moon's there, sun's there. It doesn't look right. I know where he's coming from. I don't know the answer. I think it's got everything to do with angles and distances and that sort of thing.

[00:02:28] [SPEAKER_06] It does. It's actually got a little bit more than that. I don't know where Justin is. He's on Earth. For starters. So he's on Earth. That narrows it down quite a bit.

[00:02:40] [SPEAKER_04] I'm going to guess Northern Hemisphere, although I've got a 50% chance of being right. Actually, it's more than that, because more people live in the Northern Hemisphere.

[00:02:49] [SPEAKER_06] Yes, that's right. And it depends a bit on your latitude as well. But so let me answer that as if Justin's in Australia, because one of the things I was going to say was we have pretty clear skies. We have very high atmospheric transparency here. And that helps in this sort of situation. OK. So, yeah.

[00:03:12] [SPEAKER_06] So what you're looking at is after sunset, when the moon is in its crescent phase, the sun goes down and the crescent moon is very obvious, basically in the in the in the western sky. And it follows the sun down as the sun sets. The moon sets not very long afterwards. So in the morning, it's the same sort of thing, but in reverse. The sun rises.

[00:03:41] [SPEAKER_06] But the crescent moon is still about the same angular distance from the sun. You know, you can say, well, if it was, for example, 45 degrees or 40 degrees or something like that, it would be still about that little bit more, perhaps. Or I beg your pardon, a little bit. Yeah, a little bit more as it as because you're talking about a new moon.

[00:04:09] [SPEAKER_06] The crescent moon is going to swell to become a first quarter moon. And that means its distance from the sun is getting bigger in angular terms. So forget about that bit. But the bottom line is it's it's not that much different in the morning sky. So what happens is the moon that the sun rises and then the moon rises after it, if it's say 40 degrees away, it will it will rise later.

[00:04:31] [SPEAKER_06] And so you'll you'll be able to see the two of them in the sky looking very similar to what they look the previous night, except they're the other way around. The sun's higher in the sky than the moon is. And then as the two of them progress their way through the sky during the day, the sun eventually will set and the moon, the crescent moon will will follow it. That's that's the answer. I'm not sure whether I've expressed it very well, but that's the bottom line.

[00:04:57] [SPEAKER_04] No, I get that. But again, it's it's it. I still struggle to get my head around the the light source that's illuminating the moon and the way it looks to us from our perspective. You know, it did sometimes just doesn't make sense to me. And I think that's where Justin was coming from, too. I just yeah, I try to try to understand.

[00:05:24] [SPEAKER_04] I can try to think in my mind, OK, where is the sun right now? And why? Yeah, sometimes it's obvious. Other times, I think that just doesn't seem right.

[00:05:33] [SPEAKER_06] Hmm. I think it's probably most obvious when it's at first or last quarter, because then it is basically half, you know, half the moon is being. You know, half the moon is always being illuminated. What changes is how much of that half moon we can see. And that new moon, you can't see any of it because it's all on the on the others on the sunward side of of the moon. But as the moon moves through its orbit, you see more and more of the illuminated side till it's a half moon.

[00:06:02] [SPEAKER_06] And then it turns into a gibbous moon more than a half moon as it as it sort of goes around in its orbit. In some ways, you might it's maybe best illustrated by by a model. And often people hold up a tennis ball and sort of show how it's lit up by a lamp or the sun or whatever. And you can sort of imagine how the phases change as we see the moon.

[00:06:25] [SPEAKER_04] Hmm. Gibbous moon. Where did that name come from?

[00:06:29] [SPEAKER_06] Gibbous means fat. Oh, yep.

[00:06:33] [SPEAKER_04] Right. That's where it came from. I saw a gibbons moon once at the zoo wasn't pretty.

[00:06:39] [SPEAKER_06] Anyway, a gibbons moon is just a bit different from a gibbous moon.

[00:06:43] [SPEAKER_04] It's definitely not pretty at all. Hmm. I hope that answered your question, Justin. And thanks for sending us in, sending it into us is what I meant to say. This is Space Nuts with Andrew Dunkley and Professor Fred Watson. We'll go straight on to our next question. It's an audio question. This one comes from Paul.

[00:07:03] [SPEAKER_01] Hello there. My name is Paul and I'm from Salt Lake City, Utah. Been listening to the show for as long as it's been out. The one thing that I don't hear often on the show and would love an explanation on is the great attractor. Is there anything in particular that we do know about it? If so, what is it? I love the show so much.

[00:07:29] [SPEAKER_01] Mr. Dunkley, Professor Fred Watson, astronomer at large. Love you guys so much. Thank you for taking the time. Bye-bye.

[00:07:38] [SPEAKER_04] Thank you, Paul. Hope all is well in Utah as things start to freeze over. I think it's a, it's a pretty cold state that one, isn't it? Utah in the winter. I think just about everything's cold in the Northern hemisphere in, in winter. On our recent trip to the, the Balkans, it's going into, um, into winter. They're in mid autumn at the moment. And, um, yeah, we had a couple of pretty chilly days and I noticed snow already on the mountains in, in Bulgaria.

[00:08:07] [SPEAKER_04] So, yeah, but we were ready for it. No, we weren't. We're Australian. We hate the cold. Um, the great attractor. I can tell you, Paul, that it's great and it's an attractor. Uh, and that's about as much as I know.

[00:08:21] [SPEAKER_06] I thought it was the John Deere or the massive. It's Massey Ferguson.

[00:08:25] [SPEAKER_04] Yeah. The John Deere. I think.

[00:08:27] [SPEAKER_06] Yeah. So what is it? Um, it's, it's something that, um, it goes back to, I guess the 1980s when people first started, uh, looking at the great attractor.

[00:08:40] [SPEAKER_06] Um, uh, it's basically, um, uh, something massive in the universe, in our local universe, not very far away, maybe 250 million light years away in that in galactic time. Um, and it, it basically pulls on our galaxy and our companion galaxies, which are known as the local group.

[00:09:10] [SPEAKER_06] So, uh, we are heading to the greater tractor at a speed in the region of 600 kilometers per second. It's pulling us towards it. Uh, now we will actually never get there because eventually the. The expansion of the universe will overcome that 600 kilometers per, per second.

[00:09:32] [SPEAKER_04] I thought of that just as you said it.

[00:09:34] [SPEAKER_06] Yeah. So that, so that we. I did.

[00:09:37] [SPEAKER_04] Oh, good.

[00:09:38] [SPEAKER_06] Yeah. You should have said it. No, I knew you would. Yeah. So it's never going to, there's never going to be a collision. Um, the reason why it's mysterious is its direction. It's in the plane of the Milky Way, what we call the zone of avoidance that goes back before we knew that galaxies were galaxies. The zone of avoidance was the region around the Milky Way where you don't see any galaxies. And that's because the dust in the Milky Way blocks our view towards them.

[00:10:09] [SPEAKER_06] So, um, um, it's in the plane of the Milky Way. That means we're sort of, if you think of, uh, our sun and planets sitting in the disc, the spiral disc of the Milky Way, and then imagine looking at something that's on the other side of that disc, which is what the greater tractor is, you realize that you're never going to see it with, with visible light telescopes. You can with radio telescopes though. Okay. And, uh, and infrared telescopes, you can penetrate some of this dust.

[00:10:37] [SPEAKER_06] So, uh, what we know is that there is a huge amount of solar mass there. Um, it's, it'll be both visible and dark matter, which is probably not one, but a whole lot of cluster, of clusters of galaxies. And sometimes it's called a super cluster when you've got a cluster of clusters.

[00:11:04] [SPEAKER_06] Uh, and in fact, this particular one has a name, even though we can't see most of it because it's in the zone of avoidance. Uh, it's called the, the, the Laniachia super cluster. Um, and it's basically pulling our Milky Way and many, many other galaxies, uh, in this, in our local group and others towards it, uh, towards the greater tractor, which is how it got its name. But as I said, we'll never collide with it because the expansion of the universe,

[00:11:33] [SPEAKER_06] we'll eventually overcome that, that, um, mad dash towards each other. Uh, so yeah. So people are still, um, using, well, X-ray telescopes, uh, radio and infrared surveys, as I mentioned before, to look at the structures, um, which exist within this. And, and we can identify not just the greater tractor itself, but the, the clusters of galaxies that sit within it, because the greater tractor is a cluster of clusters.

[00:12:02] [SPEAKER_06] And so we can see these individual clusters now. Um, it's, yes, it's really quite remarkable that this object, um, is there. We don't talk about it that much because there's just a few scientists who are studying that cluster of clusters. But, um, it's not anything that in a set, you know, it's not one of the big mysteries of the universe, if I can put it that way, which is why Space Nuts doesn't talk about it all that often.

[00:12:31] [SPEAKER_04] Yeah. Although we have, we have discussed that a couple of times in the past. We have, we have. Um, yeah.

[00:12:38] [SPEAKER_06] There's a number of YouTube videos, um, that, that talk about it. So, um, you know, Paul might usefully get online and just have a look at some of these YouTube videos that will probably give you a much more succinct, uh, answer than the adequate one that you've just had.

[00:12:54] [SPEAKER_04] Or, or Paul can go to where I've just gone, amazon.com. Mm-hmm. And he can buy a copy of The Great Book of Tractors. Which, which includes John Deere, Caterpillar, Massey Ferguson, International. I'm not joking. Yeah. I'm not joking. It is, there is such a book.

[00:13:18] [SPEAKER_04] So, um, that might not answer his question, but at least he'd know which, and you know, they have a tractor of the month thing as well. Oh, and they should then- The Great Attractor has never won that.

[00:13:31] [SPEAKER_06] No, we should have a Great Attractor of the month really in- Yes, we should. In astronomy. Yeah. Yep.

[00:13:38] [SPEAKER_04] There it is. Um, thank you, Paul. Great question. Lovely to hear from you. Hope you can stay warm in Utah in the coming months. This is Space Nuts with Andrew Dunkley and Professor Fred Watson.

[00:13:51] [SPEAKER_02] I believe that this nation should commit itself to achieving the goal before this decade is out of landing a man on the moon and returning him safely to the earth.

[00:14:04] [SPEAKER_04] I'm actually so glad that Paul asked that question because it's been way too long since I did the Great Attractor joke. And I really love that one.

[00:14:13] [SPEAKER_05] Yeah.

[00:14:13] [SPEAKER_04] Our next question, Fred, comes from Bob. You put no limit on the size of a moon. Considering the billions to trillions of Saturn's ring particles, do we need to add has cleared its orbit to our definition of a moon?

[00:14:34] [SPEAKER_04] Now, we've had a few questions recently and maybe Bob asked one before about defining a moon when, you know, when does a moon become a moon by our definition? Uh, and now he's sort of another little tricky point to throw into the mix.

[00:14:49] [SPEAKER_06] Um, yeah, except that there are objects which we definitely accept as moons, which are embedded in the, in the rings of Saturn. Um, so, and in fact, to some extent, shepherd the rings of Saturn, if I put it that way, gravitationally keep them in the right spot. Um, so, uh, I do like the idea though, Bob's idea, which comes from our definition of a planet. A planet is an object that's orbiting the sun in the case of solar system planets.

[00:15:19] [SPEAKER_06] It's orbiting the sun. It's big enough for its own gravity to pull it into a spherical shape. And it's cleared the, the area around it of debris. So it's become the most gravitationally dominant object within that region. And I don't think you can say that about the little moons of Saturn that are embedded in the rings, even though they probably are the most dominant gravitational objects because they do shepherd the rings. Um, but it's a good point.

[00:15:48] [SPEAKER_06] You know, it's embarrassing that we don't have a lower limit, uh, for, for what, what counts as a moon.

[00:15:58] [SPEAKER_04] In which case you could question the authenticity of Phobos and Deimos, maybe. Yeah, well, um, maybe you could find out, cause we spoke about it in the last episode. If we find out with this new mission that they're asteroids.

[00:16:20] [SPEAKER_06] That's right. Captured asteroids. Um, yes. Uh, look, it's, it's, it's, you know, basically it's a, it's a, it's an open question. Um, I'm just looking at a nice little piece here from the National Air and Space Museum. What makes a moon a moon? A moon is a planetary body that goes around another planetary body.

[00:16:45] [SPEAKER_06] Usually this is one or, usually this is one or more moons going around a planet, but it doesn't have to be a planet. But once again, uh, nobody bothers defining, uh, what a small, you know, what the size limit is. Yeah. So yeah. Interesting stuff. We, we need to get that sorted out, I think.

[00:17:03] [SPEAKER_04] But we don't put a size limit on planets, do we?

[00:17:07] [SPEAKER_06] No, we don't. Uh, in terms of the, yes. So like, yeah, exactly. So Mercury is clearly a planet, even though it's actually smaller than some of the moons of the other, of the gas giants. Yeah. Smaller than Ganymede and smaller than Titan. But it's still a planet because it's the only object in that region of the solar system. And it is spherical.

[00:17:27] [SPEAKER_04] What if you had two objects orbiting each other? Like two Earths. Yeah. Would you define them both as planets or one would have to be a moon?

[00:17:40] [SPEAKER_06] So there's, there is a definition there. Uh, if their center of mass, um, in other words, something we call the barycenter, the center of gravity of the two. If it's outside of both of them, in other words, they're kind of orbiting around a common center of mass. Uh, then what you've got is a binary planet. Uh, it's not a planet and a moon. Um, you've got a binary planet and technically that's what Pluto is.

[00:18:10] [SPEAKER_06] Pluto and its moon, uh, Charon, which is the, the center of mass is actually outside the body of Pluto. Yeah. So, so Pluto and Charon really should be considered a binary dwarf planet because they're both spherical and they're, yeah.

[00:18:27] [SPEAKER_04] They are. And that makes me wonder why we don't consider the shape when defining a moon too. I mean, should, should it, I mean, maybe I'm just being idealistic, but shouldn't it be spherical?

[00:18:42] [SPEAKER_06] Um, well that would rule out Phobos and Deimos. Yeah, that's what I'm saying. And it would rule out, you know, probably 200, 250 of the moons of Saturn. I think 297 or something.

[00:18:54] [SPEAKER_04] Well that's too many, that's just greed.

[00:18:56] [SPEAKER_06] Um, yeah, Saturn's very replete with moons, but most of them are odd shapes. Some of them are very interesting indeed. Um, yeah. So, uh, but yes, there's a loose end there in astronomy. I need to check a little bit further. The International Astronomical Union might have a definition of a moon that's better than what I've just been pulling out of the back of my head. Maybe.

[00:19:20] [SPEAKER_04] Yeah. But, uh, it is, it is kind of a gray area all up, uh, and no pun intended cause that's basically the color of ours, but, um. It's the color of the back of my head as well. Yeah. Yeah. Only the back though, yeah. Yeah. Hmm. All right. Um, it's a, it's a really good question and, uh, there is, yeah, and, and he brings up a really valid point. So. Hmm. Yeah.

[00:19:48] [SPEAKER_04] So maybe, maybe he should file that one, send it into them and say, look, have you considered this? And they might go, Oh, you know what? We should. And that'll change everything. You never know. Thank you, Bob. Um, great to hear from you. And, uh, thanks for sending in your question.

[00:20:06] [SPEAKER_05] Two, one.

[00:20:12] [SPEAKER_00] Two, one.

[00:20:59] [SPEAKER_00] Three, two. One, two. Three, two. Three. Two. Two, one. Two. One, two. One, one. would you be able to see planets and and the moon at night as well how it would um how it would look to the viewer also would there be any strange phenomena when the sun moves through

[00:21:23] [SPEAKER_00] the the uh the belt as well thank you so much and anything else um you can think of would

[00:21:31] [SPEAKER_04] be greatly appreciated wonderful question thanks isla i i want to know more about the book actually so maybe isla can send us a message i want to find out because you know i'm very interested in science fiction and and science fiction novels and um yeah i'd like to find out about that it might be might be my next read um but yeah what would it look like standing on a planet

[00:21:58] [SPEAKER_04] with with rings i have seen artists impressions of this and even i think they've there have been a few depictions of what you would see looking from the surface of saturn if you could stand on it out at the rings and the effect that sunlight would have uh i think it would be a glorious sight

[00:22:18] [SPEAKER_06] it would um so that's the best way to think of this is to imagine um you know you're standing on saturn as you said there's no surface so we can't do that but if you were um so first of all the rings in terms of their position would uh their position as you look at them in other words the vista

[00:22:42] [SPEAKER_06] that you see they would always be in the same direction and basically stretch from one horizon to the other um that would not change throughout the year so they would always be in the same position because you're you're standing on on the surface and these things are on the equator you've got a latitude so the two come together but what would change is their appearance and it's basically exactly

[00:23:08] [SPEAKER_06] as isla says um saturn does have seasons a lot like the earth's in the sense that i think saturn's axial tilt its obliquity the tilt to to the plane of its orbit is um about 26 degrees not that much different from our 23 and a half degrees here on planet earth so as you look at the rings um in your

[00:23:31] [SPEAKER_06] summer time they will be illuminated by the sun on the side that you can see the side of the rings that you can see yeah and so they'd be very very bright and and you wouldn't sleep at night because they'd always be lit up that um yes to some extent that's right they would uh twilight you would have the rings illuminated and in fact that's a really interesting thing you would see the

[00:23:59] [SPEAKER_06] shadow of the planet uh traversing across the rings yeah that would be quite quite something wouldn't it so so um and you get so and during the winter when the sun is below the plane of the rings because the rings are on your equator so in summer time it's above the plane of the rings in winter it's below the plane of the rings it will be illuminating the rings uh from behind and

[00:24:26] [SPEAKER_06] they're the the rings because they're made of individual particles they're not solid they're translucent so you'd still get sunlight filtering through it will probably be quite a bit dimmer but um you'd you'd get sunlight filtering through the rings um and again it would depend on your latitude you might also be able to see the sun itself directly depending on your latitude uh it's

[00:24:53] [SPEAKER_06] really all kinds of interesting phenomena in regard to unusual phenomena i guess the one that would be intriguing i think this could be quite spectacular because we've seen photos of this from the cassini spacecraft when you're very near the equinox so the sun is lighting up the ring system from the edge edge yeah um and remember the rings 250 000 kilometers across only 100 meters thick if that

[00:25:23] [SPEAKER_06] um the the any larger boulders or objects within the rings are going to cast long shadows on the ring surface and we saw that with some of the cassini images in fact one of the satellites casting these great long shadows like big spokes like big spokes that's right so you get interesting phenomena around

[00:25:46] [SPEAKER_04] about the equinoxes and would you have like little eclipses on on the planet's surface from that

[00:25:54] [SPEAKER_06] situation yes but um they only if you're on the equator yeah and if you're on the equator uh and you're at the equinox the sun's got to shine through the rings it was pretty pretty pretty dim i think um the the effect that you get and of course the rings um in winter time would cast a shadow over

[00:26:20] [SPEAKER_06] your location depending on your latitude because the sun's being blocked even though some light would filter through uh nevertheless the sun the sun's mainly being blocked by the ring system it's a great great great question great sir to put your self into that into that situation absolutely i i think it'd

[00:26:41] [SPEAKER_04] be um an extraordinary sight and i i don't think there'd be a one-size-fits-all scenario because we we know of several planets with rings and some of them are quite significant like saturn but then you get out to um is it neptune or uranus it's got the rings neptune both of them have yeah i mean

[00:27:06] [SPEAKER_04] they're not they're not big thick heavy no they're not they're much more slender so and the distance from the the sun would make a difference to the effect as well so there's all of that that comes into play really interesting stuff great question though very very left field and um i like it uh thanks isla and um wish your friend well with uh their their um their graphic novel and please tell me what it's

[00:27:33] [SPEAKER_04] called i want to know i'm desperate to know by the way fred i've finished the first draft of my sequel or prequel to the human epoch and thanks to everyone who's bought a copy it's um it's doing all right at the moment i've made about 10 bucks and um good yeah um but don't spend it all at once

[00:27:55] [SPEAKER_04] i can't there's nothing worth that and uh i'm i'm now doing the the rewrite of it the draft is just to give me the guide to actually write the story the way i want it to be written so yeah um but yeah i i'm i'm really enjoying it really enjoying it but um good so there's a little way off being ready i don't know whether to write the trilogy all in one go again or just to do one you know book one and

[00:28:24] [SPEAKER_04] then get stuck into book two after i put book one book one out there i don't i don't know i'm still pondering that this one's going to take a bit longer to formulate um but uh yeah anyway uh thanks isla thanks for your question don't forget if you've got questions please send them in to us via our website spacenutspodcast.com and spacenuts.io click on the ama tab at the top and send us uh text and audio questions one more thing fred we have not so much a question from sarah but a

[00:28:53] [SPEAKER_04] comment i've learned about the astronomy world outside of just nasa press releases and it's all your fault spacenuts has driven huge leaps in understanding what humans are doing up there i need more geordie content though uh mixed in lightly to leave in the more serious discussions on space war i didn't know my nation admitted to having bleepin golden eye up there until you mentioned it

[00:29:22] [SPEAKER_04] that came from sarah so thanks sarah that's that's a great endorsement uh really lovely um remarks and yes um sometimes you do learn things that you didn't know about um such as uh the the us government admitting they have weapons in orbit um which we did a little while back uh but yes keep those cards and letters coming in or even emails we take them too

[00:29:49] [SPEAKER_06] and thank you fred we're all done uh we'll catch again real soon sounds good andrew thank you very much for um for remembering me when you came back from the balkans it was a stretch but i managed yeah

[00:30:02] [SPEAKER_04] see you later see see you professor fred watson astronomer at large and thanks to hugh in the studio couldn't be with us today because he's out judging the greater tractor and from me andrew dunkley thanks for your company we'll see you on the next episode of space nuts bye-bye

[00:30:17] [SPEAKER_03] space nuts you'll be listening to the space nuts podcast available at apple podcasts spotify i heart radio or your favorite podcast player you can also stream on

[00:30:30] [SPEAKER_05] demand at bites.com this has been another quality podcast production from bites.com