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The Great Attractor & Saturn’s Rings: Unravelling Cosmic Questions · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: G'. Day. Thanks for joining us again on Space
• 0:02
  Nuts. My name is Andrew Dunkley, your host.
• 0:04
  I, uh, hope you're well.
• 0:06
  Coming up in a Q and A episode, we're going
• 0:08
  to be looking at the sun and the
• 0:11
  moon. Uh, a little bit of confusion going on
• 0:13
  there. It's all about the angles, I
• 0:16
  think. Uh, we're also going to, uh,
• 0:19
  see if we can tackle a question about the
• 0:21
  Great Attractor. Uh, is it John
• 0:23
  Deere or Massey Ferguson? Oh, I don't know.
• 0:27
  Uh, we're also, um, we've had
• 0:29
  this question question before, but I think
• 0:31
  this is sort of a follow up question on
• 0:33
  redefining a moon. What, you know,
• 0:36
  what defines a moon? And what do you take
• 0:39
  into account to define a moon?
• 0:41
  And finally, uh, an interesting question from
• 0:44
  someone who has a friend who's writing a
• 0:46
  graphic novel which is also science fiction
• 0:48
  and it's set on a planet that's got rings.
• 0:51
  And she's wondering about the rings. What do
• 0:54
  you see when you're standing on the planet
• 0:56
  looking up at them and how do they act and
• 0:57
  what do they do? And uh, can you put it on
• 0:59
  your finger and is it worth anything? That's
• 1:01
  all coming up on this edition of space
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  nuts.
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  Guidance is internal. 10,
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  9. Ignition sequence start.
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• 1:21
  Andrew Dunkley: Joining us again as he thunders away on
• 1:24
  his keyboard to try and answer all these
• 1:26
  questions because he's so well prepared is
• 1:28
  Professor Fred Watson Watson, astronomer lad.
• 1:30
  Hello, Fred Watson.
• 1:31
  Professor Fred Watson: I'm just writing the email I should have sent
• 1:33
  before we, uh, started.
• 1:36
  Yes,
• 1:36
  Andrew Dunkley: uh, I can wait.
• 1:39
  Professor Fred Watson: It's okay. It's fine.
• 1:41
  Andrew Dunkley: It's only 500 words. Um,
• 1:44
  shall we get straight into it and see if we
• 1:46
  can solve some of these puzzles from people?
• 1:48
  Professor Fred Watson: Yeah, yeah. I think
• 1:49
  Andrew Dunkley: Justin has sent in a question. I don't know
• 1:52
  where Justin's from. Um, probably from his
• 1:54
  house. Uh, I was at work the other morning
• 1:57
  and the sun and the moon were both in the
• 1:59
  eastern sky, yet it was a
• 2:02
  crescent moon, the same moon as the night
• 2:05
  before. How is this possible?
• 2:08
  That's a good question because I've often
• 2:10
  wondered the same thing. I'll look up and go,
• 2:12
  hang on a minute. Moon's
• 2:15
  there, sun's there. It
• 2:18
  doesn't look right. I know
• 2:21
  where he's coming from. I don't know the
• 2:22
  answer. I think it's got everything to do
• 2:25
  with angles and distances and that
• 2:28
  sort of.
• 2:28
  Professor Fred Watson: It does. It's actually got a little bit More
• 2:30
  than that, I don't know where Justin is.
• 2:33
  Um,
• 2:34
  Andrew Dunkley: he's on Earth, for
• 2:36
  starters.
• 2:37
  Professor Fred Watson: So he's on Earth, so that narrows it down
• 2:39
  quite a bit.
• 2:39
  Andrew Dunkley: I'm going to guess Northern Hemisphere,
• 2:41
  although, um,
• 2:43
  Professor Fred Watson: yeah, I've
• 2:44
  Andrew Dunkley: got a 50 chance of being right. Actually,
• 2:46
  it's more than that because more people live
• 2:47
  in the Northern hemisphere.
• 2:49
  Professor Fred Watson: Yes, that's right. Um, and it
• 2:51
  depends a bit on your latitude as well. Uh,
• 2:54
  but so let me answer that as if Justin's
• 2:57
  in Australia, um, because
• 3:00
  one of the things I was going to say was we
• 3:02
  have pretty clear skies. We have very high
• 3:04
  atmospheric transparency here, and that
• 3:07
  helps in this sort of situation.
• 3:10
  Um, so, uh, yeah, so what you're looking
• 3:13
  at is, uh, after
• 3:15
  sunset, um, when the Moon is
• 3:18
  in its crescent phase, the sun goes down,
• 3:21
  uh, and the crescent Moon is very
• 3:24
  obvious, um, basically
• 3:27
  in the western sky, and it follows the sun
• 3:30
  down. Uh, as the sun sets, the moon
• 3:33
  sets not very long afterwards. So,
• 3:36
  um, in the morning, it's the same sort
• 3:39
  of thing, but in reverse. The sun rises,
• 3:42
  but the crescent Moon is still about the same
• 3:44
  angular distance from the sun.
• 3:48
  Uh, you know, you can say, well, if it was,
• 3:50
  for example, 45 degrees or 40 degrees or
• 3:53
  something like that, um, it would be still
• 3:56
  about that little bit more, perhaps. Um,
• 3:59
  or. I beg your pardon, a little bit, uh,
• 4:01
  yeah, a little bit more. Um, as
• 4:04
  it, uh,
• 4:07
  because you're talking about a new moon, uh,
• 4:09
  the crescent moon is going to swell to become
• 4:11
  a first quarter moon, and that means its
• 4:13
  distance from the sun is getting bigger in
• 4:16
  angular terms. So forget about that bit. But
• 4:18
  the bottom line is it's not that much
• 4:20
  different, uh, in the morning sky. So
• 4:23
  what happens is the sun rises and then
• 4:26
  the moon rises after it. If it's, say, 40
• 4:28
  degrees away, it will rise later.
• 4:31
  Uh, and so you'll be able to see the two of
• 4:34
  them in the sky looking very similar to what
• 4:37
  they looked the previous night, except
• 4:38
  they're the other way around. The sun's
• 4:41
  higher in the sky than the moon is. And then
• 4:43
  as the two of them progress their way through
• 4:45
  the sky during the day, the sun eventually
• 4:47
  will set and the Moon, the crescent moon,
• 4:50
  will follow it. That's the
• 4:52
  answer. I'm not sure whether I've, uh,
• 4:54
  expressed it very well, but that's the bottom
• 4:56
  line.
• 4:57
  Andrew Dunkley: No, I get that. Um, but again,
• 5:04
  I still struggle to get my head around
• 5:07
  the light source that's illuminating the
• 5:10
  Moon. And the way it looks to us from our
• 5:13
  perspective sometimes just
• 5:16
  doesn't make sense to me. And I think
• 5:19
  that's where Justin was coming from too. I
• 5:21
  just,
• 5:22
  Professor Fred Watson: yeah,
• 5:23
  Andrew Dunkley: I try to, try to understand, try to think in
• 5:25
  my mind, okay, where is the sun right now and
• 5:27
  why? Yeah, sometimes it's obvious. Other
• 5:30
  times I think that just doesn't seem right.
• 5:33
  Professor Fred Watson: M. I think it's probably most obvious when
• 5:36
  it's at first or last quarter because then
• 5:39
  it's basically half.
• 5:42
  Half the moon is always being illuminated.
• 5:44
  What changes is how much of that half moon we
• 5:47
  can see. Uh, and at new moon you can't see
• 5:49
  any of it because it's all on the sunward
• 5:52
  side, uh, of the moon.
• 5:56
  Uh, but as the moon moves through its orbit,
• 5:58
  you see more and more of the illuminated side
• 6:01
  till it's a half moon and then it turns into
• 6:02
  a gibbous moon. More than a half moon, uh,
• 6:05
  as it sort of goes around in its orbit. Um,
• 6:08
  in some ways it's maybe best
• 6:11
  illustrated by, by a model. Um,
• 6:14
  and often people hold up a tennis ball and
• 6:16
  sort of show how, how it's lit up by a lamp
• 6:19
  or the sun or whatever. And you can sort of
• 6:21
  imagine how the phases change as we
• 6:24
  see the moon.
• 6:26
  Andrew Dunkley: Gibbous moon. Where did that name come from?
• 6:29
  Professor Fred Watson: Gibbous means, uh, fat.
• 6:31
  Andrew Dunkley: Oh,
• 6:33
  Professor Fred Watson: yep,
• 6:33
  Andrew Dunkley: right.
• 6:34
  Professor Fred Watson: That's where it came from.
• 6:36
  Andrew Dunkley: I saw a gibbons moon once at the zoo. It
• 6:38
  wasn't pretty. Anyway.
• 6:40
  Professor Fred Watson: Gibbon's moon is just a bit different from a
• 6:43
  gibbous moon.
• 6:43
  Andrew Dunkley: Ye, definitely not pretty at all.
• 6:47
  Hope, uh, that answered your question,
• 6:49
  Justin. And thanks for sending us in.
• 6:51
  Sending it into us is what I meant to say.
• 6:54
  Um, this is Space Nuts with Andrew
• 6:57
  Dunkley and Professor Fred Watson Watson.
• 6:58
  We'll go straight on to our next question.
• 7:00
  It's an audio question. M this one comes from
• 7:02
  Paul.
• 7:03
  Paul: Hello there. My name is Paul and I'm from
• 7:06
  Salt Lake City, Utah. Been listening to the
• 7:09
  show for as long as it's been out.
• 7:12
  The one thing that I don't hear often on the
• 7:15
  show and would love an explanation on
• 7:19
  is the Great Attractor. Is there
• 7:21
  anything in particular that we do know about
• 7:24
  it? If so, what is it?
• 7:27
  I love the show so much, Mr.
• 7:30
  Dunkley. Professor Fred Watson Watson,
• 7:32
  astronomer at large. What do you care? So
• 7:35
  much. Thank you for taking the time. Bye bye.
• 7:39
  Andrew Dunkley: Thank you, Paul. Hope all is well in Utah as
• 7:41
  things start to freeze over. I think it's uh,
• 7:44
  a. It's a pretty cold state that one, isn't
• 7:46
  it? Utah in, in the winter. Just about
• 7:48
  everything's cold in the northern hemisphere
• 7:50
  in, in winter. On our recent trip
• 7:53
  to the the Balkans, it's going
• 7:56
  into, um, into winter. They're in mid autumn
• 7:59
  at the moment. And, um, yeah, we had a couple
• 8:02
  of pretty chilly days and I noticed snow
• 8:04
  already on the mountains in, in
• 8:06
  Bulgaria, so. Yeah, but we
• 8:09
  were ready for it. No, we weren't. We're
• 8:11
  Australian. We hate the cold. Um, the
• 8:14
  Great Attractor. I can tell you, Paul, that
• 8:16
  it's great and it's an attractor, and that's
• 8:18
  about as much as. I know.
• 8:21
  Professor Fred Watson: I thought it was the John Deere or the
• 8:23
  massive Massey
• 8:24
  Andrew Dunkley: Ferguson. Yeah, the John Deere, I think.
• 8:27
  Yeah.
• 8:28
  Professor Fred Watson: So what is it?
• 8:30
  It's. It's something that, um, it goes back
• 8:32
  to, I guess, the 1980s, when
• 8:35
  people first started, uh,
• 8:38
  looking at the Great Attractor.
• 8:40
  Um, uh,
• 8:42
  it's basically,
• 8:46
  um, uh, something
• 8:48
  massive in the universe,
• 8:51
  in our local universe, not very far away,
• 8:53
  maybe 250 million light years away. And that
• 8:56
  in galactic terms is relatively
• 8:59
  close by. Um, and it
• 9:03
  basically pulls on our
• 9:05
  galaxy and our companion galaxies, which
• 9:08
  are known as the Local Group. So, uh,
• 9:11
  we are heading to the Great
• 9:14
  Attractor at, uh, a speed in the region
• 9:17
  of 600 kilometres per second. It's pulling us
• 9:20
  towards it. Uh, now we
• 9:22
  will actually never get there because
• 9:25
  eventually the expansion
• 9:28
  of the universe will overcome that. 600
• 9:30
  kilometres per per second.
• 9:32
  Andrew Dunkley: I thought of that just as you said it.
• 9:34
  Professor Fred Watson: Yeah. So that. So the
• 9:36
  Andrew Dunkley: most. I did.
• 9:37
  Professor Fred Watson: Oh, good. Yeah, you should
• 9:40
  have said it.
• 9:41
  Andrew Dunkley: No, I knew you would.
• 9:42
  Professor Fred Watson: Yeah. So it's never gonna.
• 9:45
  There's never going to be a collision.
• 9:48
  Um, the reason why it's mysterious is
• 9:51
  its direction. It's in the plane of the
• 9:53
  Milky Way, what we call the zone of
• 9:55
  avoidance. That, uh, goes back before we knew
• 9:58
  that galaxies were galaxies. The zone of
• 10:00
  avoidance was the region around the Milky Way
• 10:02
  where you don't see any galaxies. And that's
• 10:04
  because the dust in the Milky Way blocks our
• 10:07
  view towards them. So,
• 10:09
  um, um, it's in the plane of the Milky
• 10:12
  Way. That means we're sort of. If you think
• 10:14
  of, uh, our sun and planets
• 10:17
  sitting in the disc, the spiral disc of the
• 10:19
  Milky Way, and then imagine looking at
• 10:22
  something that's on the other side of that
• 10:24
  disc, which is what the Great Attractor is,
• 10:26
  you realise that you're never going to see
• 10:28
  it. With visible light telescopes you can.
• 10:31
  With radio telescopes, though, and, uh,
• 10:34
  and infrared telescopes, you can penetrate
• 10:36
  some of this dust. So, uh, what we
• 10:39
  know is that there is a
• 10:42
  huge amount of
• 10:45
  solar mass there. Um,
• 10:48
  it'll be both visible and dark matter, which
• 10:51
  is probably not one, but
• 10:54
  a whole lot of cluster of
• 10:57
  Clusters of galaxies. And sometimes
• 11:00
  it's called a supercluster when you've got a
• 11:02
  cluster of clusters. Uh, and in fact,
• 11:05
  this particular one has a name, even though
• 11:08
  we can't see most of it because it's in the
• 11:10
  zone of avoidance.
• 11:11
  Uh, it's called the Laniakea
• 11:14
  Supercluster. Um, and it's
• 11:17
  basically pulling our, uh, Milky Way
• 11:20
  and many, many other galaxies, uh,
• 11:24
  in our Local Group and others towards it,
• 11:27
  um, towards the Great Attractor, which is how
• 11:29
  it got its name. But as I said, we'll never
• 11:31
  collide with it because the expansion of the
• 11:33
  universe will eventually overcome that,
• 11:36
  um, mad dash towards each other. Uh,
• 11:39
  so, yeah, so people are still, um, using,
• 11:42
  well, x ray telescopes, uh, radio and
• 11:45
  infrared surveys, as I mentioned before, to
• 11:48
  look at the structures, um, which
• 11:51
  exist within this. And we can identify
• 11:55
  not just the Great Attractor itself, but the,
• 11:57
  the clusters of galaxies that sit within it.
• 12:00
  Because the Great Attractor is a cluster of
• 12:02
  clusters. And so we can see these
• 12:04
  individual clusters now. Um,
• 12:07
  it's. Yes, it's really quite remarkable that
• 12:10
  this object is there.
• 12:13
  We don't talk about it that much because
• 12:15
  there's just a few scientists who are
• 12:18
  studying that cluster of clusters.
• 12:21
  But, um, it's not anything that in
• 12:24
  a. You know, it's not one of the big
• 12:26
  mysteries of the universe, if I can put it
• 12:27
  that way. Which is why Space Nuts doesn't
• 12:30
  talk about it all that often.
• 12:32
  Andrew Dunkley: Although we have, we have, we have done a
• 12:34
  couple of times in the past.
• 12:37
  Professor Fred Watson: Yeah, there's a number of YouTube
• 12:40
  videos, um, that talk about it.
• 12:42
  So, um, you know, Paul might usefully
• 12:45
  get online and just have a look at some of
• 12:47
  these YouTube videos that will probably give
• 12:49
  you a much more succinct, uh, answer
• 12:52
  than the adequate one that you've just had.
• 12:54
  Ah.
• 12:54
  Andrew Dunkley: Or. Or Paul can
• 12:57
  go to where I've just gone
• 12:59
  Amazon.com and he can
• 13:01
  buy a copy of the Great Book of Tractors,
• 13:06
  which, which includes
• 13:09
  John Deere, Caterpillar, Massey Ferguson
• 13:11
  International. I'm not joking.
• 13:14
  Professor Fred Watson: Yeah,
• 13:15
  Andrew Dunkley: I'm not joking. There is such a book.
• 13:18
  So, um, that might not answer his question,
• 13:22
  but at least he'd know which. And, you know,
• 13:24
  they have a Tractor of the Month thing
• 13:27
  as well. And this greater tractor
• 13:30
  has never won that.
• 13:31
  Professor Fred Watson: No, we should have a greater Tractor of the
• 13:33
  Month, really.
• 13:34
  Andrew Dunkley: Yes, we should.
• 13:35
  Professor Fred Watson: Uh, in Astronomy.
• 13:37
  Andrew Dunkley: Yeah.
• 13:37
  Professor Fred Watson: Yep,
• 13:38
  Andrew Dunkley: there it is. Um, thank you, Paul. Great
• 13:40
  question. Lovely to hear from you. Hope you
• 13:42
  can stay warm in Utah in the coming months.
• 13:45
  This is Space Nuts with Andrew Dunkley
• 13:48
  and Professor Fred Watson Watson.
• 13:51
  Speaker G: I believe that this nation should commit
• 13:53
  itself to achieving the goal
• 13:56
  before this decade is out, of landing a
• 13:59
  man on the moon and returning him safely to
• 14:01
  the Earth. These nuts.
• 14:04
  Andrew Dunkley: I'm actually so glad that Paul asked that
• 14:06
  question because it's been way too long since
• 14:09
  I did the Great Attractor joke and I,
• 14:12
  I really love that one.
• 14:13
  Yeah. Our next question, Fred Watson,
• 14:16
  comes from Bob. Um, you put
• 14:19
  no limit on the size of a moon.
• 14:22
  Considering the billions to trillions of
• 14:25
  Saturn's ring particles, do we
• 14:28
  need to add has cleared its
• 14:30
  orbit to our definition of a
• 14:33
  moon. Now, we've had a few questions
• 14:36
  recently, and maybe Bob asked one before
• 14:38
  about defining a moon when, you know, when
• 14:41
  does a moon become a moon by our definition?
• 14:44
  Uh, and now he's sort of another little
• 14:46
  tricky point to throw into the mix.
• 14:50
  Professor Fred Watson: Um, yeah, except that there are
• 14:52
  objects which we definitely accept as moons
• 14:55
  which are embedded in the, in the rings
• 14:58
  of Saturn. M so, and in fact,
• 15:01
  to some extent shepherd the rings of Saturn,
• 15:04
  if I can put it that way, gravitationally
• 15:06
  keep them in the right spot. Um, so,
• 15:08
  uh, I do like the idea though, Bob's idea,
• 15:11
  which comes from our, ah, definition of a
• 15:14
  planet. A planet is an object that's orbiting
• 15:16
  the, um, sun. In the case of solar system
• 15:18
  planets, it's orbiting the sun. It's big
• 15:21
  enough for its own gravity to pull it into a
• 15:23
  spherical shape and it's cleared
• 15:25
  the area around it of
• 15:28
  debris. So it's become the most
• 15:30
  gravitationally dominant object within
• 15:33
  that region. And I don't think you can
• 15:36
  say that about the little moons
• 15:39
  of Saturn that are embedded in the rings,
• 15:41
  even though they probably are the most
• 15:43
  dominant gravitational objects, because they
• 15:45
  do shepherd the rings. Um, but it's a
• 15:48
  good point. You know, it's embarrassing that
• 15:50
  we don't have a lower limit, uh,
• 15:53
  for, for what,
• 15:56
  what counts as a moon.
• 15:59
  Andrew Dunkley: In which case you could question the
• 16:01
  authenticity of Phobos and
• 16:04
  Demos. Maybe.
• 16:06
  Professor Fred Watson: Yeah, well, um, maybe
• 16:09
  Andrew Dunkley: we find out, as we spoke about it in the last
• 16:11
  episode, if we find out with this new
• 16:14
  mission that
• 16:17
  they're asteroids.
• 16:20
  Professor Fred Watson: That's right. Captured asteroids.
• 16:22
  Um, yes.
• 16:25
  Look, it's, it's,
• 16:28
  it's, you know,
• 16:32
  basically it's a, it's a, it's an open
• 16:34
  question. Um, I'm just looking at a nice
• 16:37
  little piece here from the National Air and
• 16:39
  Space Museum. What makes a moon a moon? A
• 16:42
  moon is a planetary body that goes around
• 16:43
  another planetary body. Usually this is one,
• 16:46
  or usually this is one or more moons going
• 16:48
  around a planet. But it doesn't have to be a
• 16:50
  planet. But once again, nobody
• 16:53
  bothers defining, uh, what a
• 16:55
  small. You know, what the size limit is.
• 16:58
  Andrew Dunkley: Yeah.
• 17:00
  Professor Fred Watson: So, yeah, interesting stuff. We, we need to
• 17:02
  get that sorted out, I think. But
• 17:03
  Andrew Dunkley: we don't put a size limit on planets, do we?
• 17:07
  Professor Fred Watson: No, we don't. Uh, in terms of, uh.
• 17:10
  Yes. So m. Like. Yeah, exactly. So Mercury is
• 17:13
  clearly a planet, even though it's actually
• 17:14
  smaller than some of the moons of the other
• 17:17
  of the gas giants, smaller than Ganymede and
• 17:20
  smaller than Titan. But it's still a planet
• 17:22
  because it's the only object in that region
• 17:24
  of the solar system and it is spher.
• 17:27
  Andrew Dunkley: What if you had two objects
• 17:31
  orbiting each other,
• 17:33
  like two Earths? Uh,
• 17:35
  Professor Fred Watson: yeah.
• 17:37
  Andrew Dunkley: Would you define them both as planets or. One
• 17:39
  would have to be a moon.
• 17:41
  Professor Fred Watson: So there is a definition there. Uh,
• 17:44
  if their centre of mass,
• 17:46
  um, in other words, something we call the
• 17:48
  barycenter, the centre of gravity of the two,
• 17:51
  if it's outside of both
• 17:54
  of them, in other words, they're kind
• 17:57
  of orbiting around a common centre of mass,
• 18:00
  then what you've got is a binary planet.
• 18:04
  Uh, it's not a planet and a moon.
• 18:06
  Um, you've got a binary planet and
• 18:08
  technically that's what Pluto is. Pluto and
• 18:11
  its moon, Charon, uh, which
• 18:14
  is the centre of mass, is actually outside
• 18:17
  the body of Pluto. Yeah. So
• 18:20
  Pluto and Charon really should be considered
• 18:22
  a binary dwarf planet because they're both
• 18:25
  spherical and. Yeah,
• 18:27
  Andrew Dunkley: they are. Ah. And that makes me wonder why
• 18:30
  we don't consider the shape
• 18:34
  when defining a moon too. I mean, should it.
• 18:37
  Um. Maybe I'm just being idealistic, but
• 18:40
  shouldn't it be spherical?
• 18:42
  Professor Fred Watson: Um, well, that would rule out Phobos and
• 18:45
  Deimos.
• 18:45
  Andrew Dunkley: Yeah, that's what I'm saying.
• 18:46
  Professor Fred Watson: And it would rule out, you know, probably
• 18:49
  200, 250 of the moons of Saturn. Um,
• 18:52
  I think 297. That's
• 18:54
  Andrew Dunkley: just greed.
• 18:58
  Professor Fred Watson: Um, yeah, Saturn's very replete with moons,
• 19:00
  but most of them are odd shapes. Some of them
• 19:03
  are very interesting indeed. Um,
• 19:06
  yeah, so, um. But yes, there's a loose
• 19:09
  end there in astronomy. Uh, I need to check a
• 19:11
  little bit further.
• 19:12
  Ah, the International Astronomical Union
• 19:15
  might have a definition of a moon that's
• 19:17
  better than what I've just been pulling out
• 19:18
  of the back of my head.
• 19:20
  Andrew Dunkley: Maybe. Yeah. But, uh, it is, it is
• 19:23
  kind of a grey area all up. Uh, and no
• 19:26
  pun intended, because that's basically the
• 19:27
  colour of ours. But,
• 19:29
  Professor Fred Watson: um, it's the colour of the back of my head as
• 19:31
  well. Yeah.
• 19:33
  Andrew Dunkley: Only the Back, though. Yeah.
• 19:37
  All right. Um, it's a. It's a really good
• 19:40
  question. And, uh, there is.
• 19:43
  And he brings up a really valid point,
• 19:46
  so.
• 19:47
  Professor Fred Watson: Hm. Yeah, maybe.
• 19:50
  Andrew Dunkley: Maybe he should file that one, send it into
• 19:52
  them and say, look, have you considered this?
• 19:54
  And they might go, oh, you know what? We
• 19:57
  should. And that'll change everything.
• 20:00
  You never know. Thank you, Bob. Um, great
• 20:03
  to hear from you and, uh, thanks
• 20:06
  for sending in your question.
• 20:10
  Generic: 3, 2, 1.
• 20:12
  Speaker H: Space nuts.
• 20:14
  Andrew Dunkley: Our final question today, Fred Watson's a
• 20:16
  little bit different, comes from Isla.
• 20:19
  Isla Miller: Hi, my name's Isla Miller. I'm from
• 20:22
  Perth, Western Australia. First of all, I
• 20:25
  just wanted to say thank you so much for
• 20:27
  everything you do. Um, I've been listening to
• 20:29
  the podcast for so long, so it's,
• 20:32
  um, been really wonderful to listen along.
• 20:36
  My question's actually in relation to a
• 20:39
  graphic novel that my friend's writing.
• 20:42
  So the graphic novel takes place on a
• 20:44
  rocky planet that has a ring around it.
• 20:48
  And I guess we understand how the
• 20:50
  ring would appear to move through the
• 20:53
  sky as the planet has seasons, much
• 20:56
  like Earth. But our question is
• 20:59
  how would it appear to the viewer who's
• 21:01
  standing on the planet? So what would it look
• 21:04
  like during the day? What would it look like
• 21:06
  at night? Um, also, I
• 21:09
  guess, would you be able to see planets
• 21:12
  and the moon at night as well?
• 21:16
  Um, how it would look to the viewer?
• 21:19
  Also, would there be any strange phenomena
• 21:22
  when the sun moves through
• 21:24
  the, uh, the belt as well?
• 21:28
  Thank you so much. And anything else, um, you
• 21:31
  can think of would be greatly appreciated.
• 21:34
  Andrew Dunkley: Wonderful question. Thanks, Isla.
• 21:36
  I. I want to know more about the book,
• 21:37
  actually, so maybe Isla can
• 21:40
  send us a message. I want to find out
• 21:42
  because, you know, I'm very interested in
• 21:45
  science fiction and, and science fiction
• 21:47
  novels and, um,
• 21:49
  yeah, I'd like to find out about that. It
• 21:52
  might be. Might be my next read. Um,
• 21:55
  but, yeah, what would it look like standing
• 21:57
  on a planet with. With rings? I have seen
• 22:00
  artists impressions of this and even, uh,
• 22:03
  I think they have been a few depictions of
• 22:06
  what you would see looking from the surface
• 22:09
  of Saturn if you could stand on it out at the
• 22:11
  rings, and the effect that sunlight would
• 22:13
  have. I, uh, think it would be a glorious
• 22:16
  sight.
• 22:19
  Professor Fred Watson: It would, um. So that's the best way to think
• 22:21
  of this, is to imagine, um, you know, you're
• 22:24
  standing on Saturn. As you said, there's no
• 22:26
  surface, so we can't do that. But if you
• 22:28
  were, um. So first of all,
• 22:32
  the rings, in terms of their
• 22:35
  position, would
• 22:39
  their position as you look at them, in other
• 22:41
  words, the Vista that you see, they would
• 22:44
  always be in the same direction and
• 22:47
  basically stretch from one horizon to the
• 22:49
  other. Um, that would not
• 22:52
  change throughout the year. Um,
• 22:55
  so they would always be in the same position
• 22:57
  because you're standing on the
• 23:00
  surface and these things are on the equator.
• 23:02
  You've got a latitude, so the two come
• 23:04
  together. But what would change is their
• 23:06
  appearance. And it's basically exactly as
• 23:08
  Isla says. Um, Saturn
• 23:11
  does have seasons a lot like the Earth in the
• 23:14
  sense that I think Saturn's axial tilt,
• 23:16
  its obliquity, the tilt to the plane of its
• 23:19
  orbit is, um, about 26
• 23:22
  degrees, not that much different from our,
• 23:23
  uh, 23 and a half degrees here on
• 23:26
  planet Earth. So as you look at the rings,
• 23:30
  um, in your summertime
• 23:32
  they will be illuminated by the sun
• 23:36
  on the side that you can see. The side of the
• 23:38
  rings that you can see?
• 23:40
  Andrew Dunkley: Yeah. And
• 23:40
  Professor Fred Watson: so they'd be very, very bright
• 23:43
  Andrew Dunkley: and you wouldn't sleep at night because
• 23:45
  they'd always be lit up
• 23:46
  Professor Fred Watson: that, um.
• 23:50
  Yes, to some extent. That's right. They
• 23:52
  would, uh, twilight, you
• 23:54
  would have the rings illuminated. And in
• 23:57
  fact, that's a really interesting thing. You
• 23:59
  would see the shadow of the planet, uh,
• 24:02
  traversing across the rings.
• 24:03
  Andrew Dunkley: Yeah,
• 24:05
  Professor Fred Watson: uh, that will be quite, quite something,
• 24:07
  wouldn't it? And you
• 24:10
  get. So. And during the winter when
• 24:13
  the sun is below the plane of the rings,
• 24:15
  because the rings are on your equator. So in
• 24:18
  summertime it's above the plane of the rings.
• 24:20
  In winter it's below the plane of the rings,
• 24:22
  it will be illuminating the rings, uh, from
• 24:25
  behind. And
• 24:28
  the rings, because they're made of individual
• 24:30
  particles, they're not solid, uh, they're
• 24:33
  translucent. So you'd still get sunlight
• 24:35
  filtering through. It would probably be quite
• 24:37
  a bit dimmer. Uh, but, um,
• 24:40
  you'd get sunlight filtering through the
• 24:42
  rings. Um, and
• 24:46
  again, it would depend on your latitude. You
• 24:48
  might also be able to see the sun itself
• 24:50
  directly, depending on your latitude.
• 24:52
  It's, uh, really all kinds
• 24:55
  of interesting phenomena in regard to
• 24:58
  unusual phenomena. I guess the one that would
• 25:00
  be intriguing, I think
• 25:03
  this could be quite spectacular because we've
• 25:05
  seen photos of this from the Cassini
• 25:07
  spacecraft when you're very near the equinox,
• 25:11
  so the sun is lighting up the ring system
• 25:13
  from the edge.
• 25:15
  Um, and remember the rings, 250,000
• 25:18
  kilometres across, the. Only 100 metres
• 25:21
  thick, if that, um,
• 25:24
  the, the.
• 25:27
  Any larger boulders or objects
• 25:31
  within the rings are going to cast long
• 25:32
  shadows on the ring surface. And we saw
• 25:35
  that with some of the Cassini images. In
• 25:37
  fact, one of the satellites Casting these
• 25:39
  great long shadows.
• 25:41
  Andrew Dunkley: Like big spokes.
• 25:42
  Professor Fred Watson: Like big spokes, that's right. So you get
• 25:45
  interesting phenomena around about the
• 25:47
  equinoxes.
• 25:48
  Andrew Dunkley: And would you have, like, little
• 25:51
  eclipses on, on the planet's surface from
• 25:53
  that situation?
• 25:55
  Professor Fred Watson: Yes, but, um, they.
• 26:00
  Only if you're on the equator. Ah,
• 26:02
  Andrew Dunkley: yeah.
• 26:03
  Professor Fred Watson: And if you're on the equator, uh,
• 26:06
  and you're at the equinox, the sun's got to
• 26:09
  shine through the rings. It was pretty,
• 26:11
  pretty dim, I think, um,
• 26:13
  the effect that you get. And of course the
• 26:15
  rings, um, in wintertime would
• 26:18
  cast a shadow over
• 26:21
  your location, depending on your latitude
• 26:24
  because the sun's being blocked, even though
• 26:26
  some light would filter through. Uh,
• 26:29
  nevertheless, the sun's mainly being blocked
• 26:31
  by the ring system. It's a great, great
• 26:34
  question. Great. Uh, to put your self into
• 26:37
  that.
• 26:37
  Into that situation.
• 26:40
  Andrew Dunkley: Absolutely. I think it'd be, um,
• 26:43
  an extraordinary sight. And I don't think
• 26:45
  there'd be a one size fits all scenario
• 26:48
  because we know
• 26:51
  of several planets with rings and
• 26:55
  some of them are quite significant, like
• 26:57
  Saturn. But then you get out to, um.
• 27:00
  Is it Neptune or Uranus that's got the rings?
• 27:03
  Neptune.
• 27:04
  Professor Fred Watson: Both of them have.
• 27:05
  Andrew Dunkley: Yeah. I mean, they're not, they're not big,
• 27:07
  thick, heavy. No,
• 27:08
  Professor Fred Watson: they're not. They're much more slender.
• 27:11
  Andrew Dunkley: So. And the distance from the, the sun
• 27:14
  would make a difference to the effect as
• 27:16
  well.
• 27:16
  So there's all of that that comes into play.
• 27:20
  Really interesting stuff. Great question,
• 27:22
  though. Very, very left field.
• 27:25
  And, um, I like it. Thanks, Isla, and
• 27:28
  wish, um, your friend well with, uh, their,
• 27:31
  Their, um, their graphic novel. And please
• 27:33
  tell me what it's called. I want to know. I'm
• 27:35
  desperate to know. By the way, Fred Watson,
• 27:37
  I've finished the first draft of my
• 27:40
  sequel or prequel to the Human Epoch. And
• 27:43
  thanks to everyone who's bought a copy, it's.
• 27:45
  It's doing all right at the moment. I made
• 27:47
  about 10 bucks and, um.
• 27:51
  Professor Fred Watson: Good.
• 27:52
  Andrew Dunkley: Yeah. Um, but don't spend
• 27:55
  Professor Fred Watson: it all at once.
• 27:56
  Andrew Dunkley: I can't. There's nothing worth that.
• 28:00
  And, uh, I'm. I'm now doing the,
• 28:03
  the rewrite of it. The draft is just to give
• 28:05
  me the guide to actually write the story the
• 28:07
  way I want it to be written. So. Yeah,
• 28:10
  um. But yeah, I, I'm. I'm really
• 28:13
  enjoying it. Really enjoying it. But, um.
• 28:15
  Professor Fred Watson: Good.
• 28:16
  Andrew Dunkley: It's a little way off being ready. I don't
• 28:18
  know whether to write the trilogy all in one
• 28:20
  go again or just to do one, you know, book
• 28:23
  one and then get stuck into book two after I
• 28:25
  Put book one, Book one out there. I don't. I
• 28:27
  don't know. I'm still pondering that
• 28:30
  this one's going to take a bit longer to
• 28:32
  formulate.
• 28:33
  Um, but, uh, yeah, anyway, thanks, uh, Isla,
• 28:36
  thanks for your question. Don't forget, if
• 28:37
  you've got questions, please send them into
• 28:39
  us via our website, space nutspodcast.com
• 28:42
  and spacenuts IO. Click on the AMA M
• 28:45
  tab at the top and send us text, uh, and
• 28:47
  audio questions. One more thing, Fred Watson.
• 28:50
  Um, we had not so much a question from Sarah,
• 28:52
  but a comment. I've learned about the
• 28:55
  astronomy world outside of just NASA press
• 28:58
  releases and it's all your fault.
• 29:00
  Space Nuts has driven huge leaps in
• 29:03
  understanding what humans are doing up there.
• 29:06
  I need more Geordie content,
• 29:09
  though mixed in lightly, to
• 29:11
  leaving the more serious discussions on
• 29:14
  space war. I didn't know my nation
• 29:17
  admitted to having bleep and
• 29:19
  goldeneye up there until you mentioned it.
• 29:22
  That came from Sarah. So
• 29:25
  thanks, Sarah, that's a great endorsement.
• 29:28
  Uh, really lovely, um, remarks.
• 29:31
  And yes, um, sometimes you do learn things
• 29:33
  that you didn't know about. Um, such
• 29:36
  as, uh, the, the U.S. government admitting
• 29:39
  they have weapons in orbit. Um, which we did
• 29:42
  a little while back.
• 29:43
  Uh, but yes, keep those cards and letters
• 29:45
  coming in or even emails. We take them too.
• 29:49
  And thank you, Fred Watson. We're all done.
• 29:51
  Uh, we'll catch again real soon.
• 29:53
  Professor Fred Watson: Sounds good. Andrew. Thank you very much for,
• 29:55
  um, for remembering me when you came back
• 29:58
  from the Balkans.
• 30:00
  Andrew Dunkley: It was a stretch, but I managed.
• 30:02
  Professor Fred Watson: Yeah. See you later.
• 30:03
  Andrew Dunkley: See. See you. Professor Fred Watson Watson,
• 30:05
  astronomer at large, and thanks to Huw in the
• 30:07
  studio. Couldn't be with us today because
• 30:08
  he's out judging the Great Attractor. And
• 30:11
  from me, Andrew Dunkley. Thanks for your
• 30:13
  company. We'll see you on the next episode of
• 30:15
  Space Nuts. Bye. Bye.
• 30:18
  Speaker J: You've been
• 30:19
  Speaker G: listening to the
• 30:19
  Speaker J: SpaceNuts podcast
• 30:22
  Generic: of
• 30:23
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• 30:25
  iHeartRadio or your favourite podcast
• 30:28
  player. You can also stream on
• 30:30
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• 30:32
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• 30:34
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