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Comets, Meteors & Celestial Wonders : A Cosmic Special · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: Hello again. Thank you for joining us on
• 0:01
  another episode of Space Nuts. My name is
• 0:04
  Andrew Dunkley, your host. It's great to have
• 0:06
  your company. As I mentioned last episode,
• 0:09
  Fred is away for a few weeks or
• 0:12
  a couple of years. Now it's a few weeks. And,
• 0:15
  uh, in his stead, we'll be joined by
• 0:17
  Professor Jonti Horner, who you know and love
• 0:20
  because he's been with us before and uh, he's
• 0:22
  a part of the team. So, uh, we will be
• 0:25
  doing over the next, uh, several episodes,
• 0:28
  um, taking a different approach. Uh, we're
• 0:31
  going to, to uh, focus on specific topics
• 0:34
  within each of the episodes. Uh,
• 0:37
  we could call them specials if you like. And
• 0:40
  today our focus will be on
• 0:42
  comets and meteors. Stick around.
• 0:45
  We're doing all of that on this episode of
• 0:47
  space nuts. 15 seconds. Guidance
• 0:50
  is internal. 10, 9,
• 0:53
  ignition sequence start.
• 0:55
  Jonti Horner: Space nuts. 5, 4, 3, 2.
• 0:57
  Andrew Dunkley: 1, 2, 3, 4, 5, 5, 4, 3,
• 1:00
  2, 1.
• 1:01
  Jonti Horner: Space nuts.
• 1:02
  Andrew Dunkley: Astronauts. Feels good and
• 1:05
  it's great to have him back. Professor Jonti
• 1:07
  Horner, professor of Astrophysics at the
• 1:10
  University of Southern Queensland. Jonti,
• 1:13
  hello.
• 1:13
  Jonti Horner: Ah, uh, hey, how are you going? Good.
• 1:15
  Andrew Dunkley: Great to see you again.
• 1:17
  Jonti Horner: Well, it's good to be back. It's something
• 1:19
  nice to keep me entertained while I'm having
• 1:20
  a little bit of a restful couple of weeks.
• 1:22
  I'm, you know, I've got a bit of leave, so
• 1:24
  I'm recovering from a minor surgery and
• 1:27
  therefore I can give my entire forecast to.
• 1:29
  Talking about fun things rather than doing
• 1:31
  admin effectively means I get to see a little
• 1:34
  bit of the life Fred gets to live.
• 1:35
  Andrew Dunkley: Yeah, maybe. Yes. Although he doesn't seem to
• 1:38
  slow down much. Um, in fact, I think
• 1:41
  the worst thing you can do when you retire is
• 1:43
  slow down because the brain matter decides to
• 1:46
  give up the ghost and that's when it's all
• 1:48
  over. Red Rover. But, uh, no, he, he's going,
• 1:51
  going great guns.
• 1:52
  And um, you didn't mention that you're having
• 1:55
  a little bit of a recuperation. Are
• 1:58
  you in a position to talk about that or
• 2:01
  too embarrassing?
• 2:03
  Jonti Horner: Well, it's one of those things that when I,
• 2:04
  when I first had this pointed out, I a bit
• 2:06
  embarrassed about it, but I don't think as
• 2:08
  bloats we ever talk about health that much
• 2:10
  until it's worth muscling past a little bit
• 2:13
  of embarrassment. So I'm in my late 40s and
• 2:16
  I went to the doctor about a year ago
• 2:18
  because, had a little bit of bleeding when I
• 2:20
  was sitting down and stuff like this and
• 2:21
  nothing dramatic. Um, But I found out two
• 2:24
  things. Firstly, in Australia, and I don't
• 2:26
  know about the rest of the world, you should
• 2:27
  look this up. But when you're in your 40s,
• 2:30
  the Medicare system here affords the
• 2:32
  opportunity for you to get health checks.
• 2:34
  Yep. Which is brilliant. So you basically get
• 2:36
  what in the UK they'd call an MOT for a car.
• 2:39
  You get everything run over and you get your
• 2:41
  blood pressure done and your heart rate done
• 2:43
  and everything else. And then you go back
• 2:44
  every three months and do it again and again
• 2:46
  and again, and it's basically you're at an
• 2:48
  edge where things start to break. Let's get
• 2:50
  on top of it early so that you can enjoy the
• 2:52
  rest of your life in peace, effectively. I
• 2:55
  think it's a really good idea and I suspect
• 2:56
  from a government point of view, makes a lot
• 2:58
  of sense, because if you find things easy
• 3:00
  earlier, they're easier and quicker and
• 3:02
  cheaper to solve. Um, what it turned out from
• 3:05
  that was I spent about two months going back
• 3:07
  and forth with a doctor who thought I had one
• 3:09
  thing wrong, which is not what it was. And
• 3:11
  then I got. Got sent to this specialist who
• 3:13
  said, you've got something called a fistula
• 3:15
  down near your backside, which, not life
• 3:18
  threatening, not the end of the world, not
• 3:19
  doomed, but it's uncomfortable. Um, and, you
• 3:22
  know, it's been slightly embarrassing in that
• 3:24
  I've had to learn more about sanitary pads
• 3:27
  and, you know, um, you would have expected,
• 3:29
  you know, which the women in the audience are
• 3:32
  going, about bloody time a man learned about
• 3:33
  this. Um, but it's a weird
• 3:36
  one because it's not life threatening. It's
• 3:38
  nothing of a problem, something 10 or 20% of
• 3:40
  guys apparently get them, but they contain
• 3:42
  multiple surgeries to fix. And when I went in
• 3:45
  for the first surgery in January, there was
• 3:48
  another guy there who was on surgery number
• 3:50
  seven.
• 3:50
  Andrew Dunkley: Wow.
• 3:51
  Jonti Horner: Which he had deep and joyous, um, kind of day
• 3:54
  surgery. But you get a full general and you
• 3:55
  go under and Dr. Does snippy, snippy things
• 3:57
  and you get a couple of weeks off work, which
• 3:59
  is where I am now. So I've just had surgery
• 4:01
  number two and the doctor is hopeful,
• 4:04
  confident, whatever, that surgery number
• 4:05
  three will be the final fix. And it's one of
• 4:08
  these weird things because people say, what's
• 4:09
  wrong with you? And if it's a sore arm, you
• 4:11
  just say, I've hurt my arm, or you've broken
• 4:13
  your arm or something. Or in Australia, a
• 4:15
  really common one, a melanoma. People have
• 4:17
  been in the sun too much going into hospital.
• 4:19
  What do you get, I've, ah, got a melanoma
• 4:20
  taken off. But as soon as it's anywhere
• 4:22
  between about your belly button and your
• 4:24
  knee, people are bashful about talking about
• 4:25
  it. And I first few months I was mortified
• 4:28
  and like, wouldn't talk about it. And
• 4:30
  realization is that if you don't talk about
• 4:32
  it, people don't get checked. And we as
• 4:35
  men are terrible for that. And so, yeah,
• 4:37
  worth talking about. I'm a bit embarrassed
• 4:39
  about it, but I shouldn't be. And it's good,
• 4:41
  it's going to tune up. And it means that in
• 4:42
  40 years time I'll still be up and kicking
• 4:45
  and having a lot of fun rather than in
• 4:47
  discomfort and grumbling about a problem I
• 4:48
  could have got fixed.
• 4:49
  Andrew Dunkley: Yeah, yeah. And, um, I think you're
• 4:52
  right. I think men do tend to keep things to
• 4:55
  themselves. Uh, a lot of them go into denial
• 4:58
  or they just think, well, no, that won't
• 5:00
  happen to me, so no problem. But,
• 5:04
  uh, when I was diagnosed with prostate
• 5:06
  cancer, it was like a bolt from the blue. And
• 5:09
  I didn't, I never expected
• 5:12
  to get it because there was next to no
• 5:14
  history of it in my family. So, um, that was
• 5:17
  a bit of a shock. And this is. How long is
• 5:20
  it now? Three years. Three years. And I'm
• 5:23
  still working my way through it. So,
• 5:27
  um, but the latest scans are all good.
• 5:30
  So fingers crossed that we've, you know,
• 5:33
  reached a good position. But, um, it's
• 5:36
  just an ongoing thing in your life. You just
• 5:37
  got to get used to it. But you. My
• 5:40
  advice to men is go and get checked. If
• 5:42
  you're over 50, go and get a
• 5:45
  prostate exam, go and get your PSA tests
• 5:48
  done. Because if you don't and
• 5:51
  then they find it, it might be too far along.
• 5:54
  Um, and then the treatment becomes more
• 5:57
  dramatic. So anyway, um, it's a good
• 6:00
  thing to bring up.
• 6:01
  Jonti Horner: It is. And it goes for the mental health
• 6:03
  stuff as well. I have a former partner of
• 6:05
  mine, kind of 20 years ago, who was very
• 6:07
  severely bipolar, had a lot of challenges
• 6:10
  and she was continually frustrated by
• 6:12
  people's responses to that in public, in that
• 6:14
  it's a hidden illness there. She's getting
• 6:17
  treatment. But what she always said is, it's
• 6:19
  really frustrating. If I, if I had a broken
• 6:21
  leg or I had an injury to my arm and people
• 6:23
  could see it, they'd be supportive. But with
• 6:26
  mental health, she got a hell of a lot of,
• 6:27
  I'll just get over it, uh, or toughen up or.
• 6:29
  Andrew Dunkley: Yep. Yeah.
• 6:30
  Jonti Horner: And, yeah, and, you know, she was female,
• 6:33
  so she's more likely to go to the doctor and
• 6:35
  talk about it. Statistically, men with mental
• 6:38
  health challenges tend to avoid that even
• 6:40
  more than they'll go to the doctor with
• 6:42
  physical health challenges. And it's
• 6:44
  something I'd like to change. I come from a
• 6:46
  working class background in Yorkshire where
• 6:48
  men m. Don't talk about anything. You know,
• 6:49
  you're meant to be stoic and the only, the
• 6:52
  only expression of emotion you're allowed is
• 6:53
  rage or a single manly tear. You know, it's,
• 6:56
  it's really creative the way we're
• 6:58
  conditioned. And even though I'm, you know, I
• 7:00
  went to uni, I've had a life, I've grown up.
• 7:02
  All this stuff still there at the back of
• 7:03
  your head and you've got to fight against it
• 7:05
  because the instinct is, ah, there's nothing
• 7:07
  wrong. I won't bother, you know. Yeah.
• 7:09
  Andrew Dunkley: And, um, yeah, you see it way too often.
• 7:12
  Um, I know it's a departure from what this
• 7:14
  podcast is all about, but I,
• 7:17
  when given the opportunity, will
• 7:20
  openly, um, say to men, um, you know,
• 7:23
  don't, don't hesitate to go to the
• 7:26
  doctor. Not, not when you think something's
• 7:29
  wrong. Just preemptively go and get. Once a
• 7:32
  year, go and get checked and make sure
• 7:33
  everything's where it's supposed to be or
• 7:36
  whatever. Um, we do it, do it for
• 7:38
  Jonti Horner: our cars, we do it for our pets.
• 7:40
  Andrew Dunkley: Yeah.
• 7:40
  Jonti Horner: Do it for yourself as well.
• 7:42
  Andrew Dunkley: Yeah, exactly.
• 7:43
  Jonti Horner: And yeah, I think it's probably a record for
• 7:44
  the quickest we've ever got off topic. And
• 7:46
  possibly we shouldn't have a trigger warning
• 7:48
  at the front of it and all the rest of it,
• 7:49
  but no good way to start even though it is
• 7:51
  off topic.
• 7:52
  Andrew Dunkley: It's okay, we'll get on to topic right now
• 7:54
  because, uh, uh, as I mentioned, these,
• 7:57
  these, uh, next, uh, several, uh,
• 8:00
  episodes are going to be dedicated to
• 8:02
  singular topics each. And today
• 8:05
  it's, uh, well, related topics. Comets and
• 8:07
  meteors. Uh, this is a, this is pet
• 8:11
  topic of yours, I imagine.
• 8:13
  Jonti Horner: It is. I, I've always been a bit more into
• 8:15
  the nearby stuff than the more distant stuff.
• 8:17
  So it always tickles me a little bit that
• 8:19
  when questions come in when I'm on the show,
• 8:21
  we get all the Big bang and cosmology ones.
• 8:23
  And I'm sure if you've got uh, someone like
• 8:25
  the wonderful Tamara Davis on to talk
• 8:26
  cosmology, she get all the planets questions.
• 8:28
  It's always the way it goes. Yeah, but comets
• 8:31
  and meteors are a big part of what hooked me
• 8:33
  into astronomy as A kid. And, um, my thinking
• 8:35
  behind this is that we're recording in
• 8:38
  advance. You know, um, obviously Fred
• 8:41
  is away, but you've got recordings with Fred
• 8:43
  already. And so the news that we would
• 8:45
  normally talk about hasn't happened yet. So
• 8:48
  I, I have many talents, but seeing into the
• 8:50
  future isn't one of them to that degree. And
• 8:52
  so I thought it better to have a discussion
• 8:54
  about the general stuff in a bit more depth
• 8:57
  than go into particular news topics. And
• 8:59
  it's. It could almost be a bit of an
• 9:01
  explainer, a bit of the background, and
• 9:03
  hopefully at least gives my insight into why
• 9:05
  a given topic's interesting, but also what
• 9:07
  people can look out for in the future and how
• 9:09
  they can get more into and more out
• 9:12
  of that particular topic, if that makes
• 9:15
  sense. Yeah, Um, a little bit different, I
• 9:17
  understand. For some listeners it might be a
• 9:19
  bit of an abrupt departure and a change. So
• 9:22
  it'll be interesting to see what feedback you
• 9:23
  get. But hopefully people like it as a little
• 9:26
  bit of a change in a breath of fresh air. And
• 9:28
  if they don't, well, there's only a couple of
• 9:29
  episodes and Fred's back anyway, so you'll
• 9:31
  have to deal with it and we'll see.
• 9:33
  Andrew Dunkley: I'm sure it'll be fine.
• 9:34
  Uh, comets and meteors are a very popular,
• 9:37
  uh, topic. So, um, uh, where do we
• 9:40
  start? Maybe, maybe look at a bit of the
• 9:41
  history of this.
• 9:43
  Jonti Horner: Yeah, I think that is always a good place.
• 9:46
  It sets the context of where we are now. And,
• 9:48
  um, for both comets and meteors, there's a
• 9:51
  kind of global connection societally that
• 9:53
  really predates by a long, long way
• 9:56
  our scientific knowledge. Essentially the
• 9:59
  modern scientific viewpoint and the
• 10:01
  scientific method. All cultures across the
• 10:03
  world, from our wonderful, uh, traditional
• 10:05
  owners here in Australia to the peoples of
• 10:07
  every continent and every land, um, both
• 10:09
  current and past, historically had a
• 10:12
  really firm connection to the night sky. They
• 10:14
  knew the night sky better than most people
• 10:15
  these days do because it wasn't light
• 10:17
  pollution, there weren't TVs and Xboxes.
• 10:20
  So the sky was something people much more
• 10:22
  exposed to. A lot of cultures have
• 10:25
  this kind of idea of as above, so below, as
• 10:27
  below, so above. So they were very firmly of
• 10:30
  the idea that major events on the Earth were
• 10:32
  reflected in the sky. And, uh, major events
• 10:35
  in the sky would have their counterparts on
• 10:37
  the Earth. And that's where astrology
• 10:40
  was born. And for a long time, astrology and
• 10:42
  astronomy were one and the same. You know,
• 10:44
  people doing astronomy studies were doing it
• 10:47
  because they wanted to understand the events
• 10:48
  that would influence what's on the Earth. And
• 10:51
  there are good examples of this in terms of
• 10:53
  the nominally fixed stars, uh, things like
• 10:55
  the ancient Egyptians using the rising of
• 10:58
  Sirius in the dawn sky after it disappeared
• 11:01
  in the evenings as a predictor of the
• 11:03
  flooding of the Nile, for example, the use of
• 11:04
  the night sky as a calendar, lots of stuff
• 11:07
  like that. But because people are so aware of
• 11:10
  the night sky, anything that was ephemeral,
• 11:13
  anything that was transitory, that appeared
• 11:15
  and then disappeared, that was unexpected,
• 11:17
  was often seen as kind of a portent or an
• 11:19
  omen, something that was an
• 11:22
  indication either of major change and
• 11:24
  upheaval currently happening or one soon to
• 11:26
  come. And really bright comets and, um,
• 11:28
  spectacular meteor showers kind of often fill
• 11:31
  this role. And you can go back through
• 11:33
  ancient history where we have the records and
• 11:36
  see good examples of this. I've got, in one
• 11:38
  of my talks, talks about a
• 11:41
  guy called, uh, Mithridates,
• 11:44
  um, Jupiter 6, I think his name was. He was
• 11:46
  one of the great enemies of the Roman Empire.
• 11:48
  And there are quotes ascribed to him saying
• 11:51
  things like, um, even the heavens predicted
• 11:54
  the greatness of this man. For in the year in
• 11:56
  which he was born and the year in which he
• 11:57
  came to reign, a comet shone through Both
• 12:00
  periods for 70 days as
• 12:02
  bright as the sun. Um, each rising and
• 12:04
  setting took four hours each. And that's kind
• 12:07
  of hyperbolic, but it gives this idea that
• 12:09
  people saw something in the sky that was
• 12:12
  unusual and tied it to events on Earth.
• 12:15
  Another good example would be the alleged
• 12:17
  comet called Caesar's Comet in 44 BC
• 12:20
  43-43, which
• 12:23
  is recorded in Roman writings from
• 12:26
  a century or two later, talking
• 12:29
  about after the death of Caesar, a comet
• 12:31
  blazed in the sky for seven days that was
• 12:34
  spectacularly bright, then disappeared and
• 12:36
  was never seen again. Now, that comet is a
• 12:38
  really good example of the challenge people
• 12:40
  have with historical records,
• 12:43
  because on the one hand you've got these
• 12:45
  clear reports from the Roman Empire, none of
• 12:48
  them at the time, though, all of them a bit
• 12:50
  later on. But that comet is not recorded from
• 12:52
  anywhere else on the planet. And there were
• 12:54
  cultures around the globe leaving records
• 12:56
  like ancient China and ancient Korea, who
• 12:58
  would have seen it. So was that comet real,
• 13:02
  or was it a case of after the event, people
• 13:04
  inventing a night sky phenomena to tie
• 13:07
  with the soul of the emperor rising to
• 13:09
  heaven? It's one of the challenges people in
• 13:11
  the kind of cultural astronomy space face, I
• 13:13
  think, in terms of disentangling the
• 13:16
  narrative from the events that prompted it,
• 13:18
  if that kind of makes sense. Yeah, but what's
• 13:21
  certainly true is, uh, for as long as we've
• 13:23
  looked at the sky, really bright comets and,
• 13:25
  um, unusually powerful meteor showers
• 13:28
  were things that people took note of. And
• 13:30
  recently there was a lot of media, media
• 13:32
  coverage of the April Lyrid meteor shower,
• 13:35
  which is not one of the strongest of the
• 13:37
  year, but one of the reasonable, moderate
• 13:40
  ones. It's kind of one that if you're a
• 13:41
  meteor enthusiast, you'll go out and watch,
• 13:43
  but isn't worth going out if you're not that
• 13:45
  interested because there's too few.
• 13:48
  I had to grumble about some of the coverage
• 13:49
  here in Australia because it's not a great
• 13:51
  shower for us. But that meteor shower
• 13:53
  was recognized by the traditional owners in
• 13:56
  Australia. And there are stories from
• 13:57
  Victoria, from, I think, the Burong people,
• 14:00
  although I stand to be corrected on that,
• 14:02
  that associate this meteor shower with the
• 14:04
  Mallee Fowl, one of the big ground nesting
• 14:05
  birds in Australia, which nests around that
• 14:08
  time of year. The meteors seen shrieking from
• 14:10
  low in the northern sky were viewed as being
• 14:12
  the dust being kicked up by the nesting bird
• 14:15
  celestially. So they recorded this meteor
• 14:17
  shower, even though it isn't a particularly
• 14:19
  strong one. But our oldest
• 14:22
  written record of any meteor shower is the
• 14:24
  April Lyrids, and it's dated back to
• 14:26
  something like 687 BCE, when
• 14:28
  stars fell like rain, when there was a major
• 14:30
  storm from the Lyrids, and it was significant
• 14:33
  enough for people to record. So comets
• 14:36
  and meteors, way before the modern
• 14:39
  scientific understanding of them really had
• 14:41
  this important cultural role,
• 14:44
  um, even in the Battle of Hastings. If you
• 14:46
  ever go to see the Bayer Tapestry, this
• 14:48
  wonderful woven record of the Battle of
• 14:50
  Hastings and the invasion of William the
• 14:52
  Conqueror, Comet Hallie features prominently
• 14:55
  on that, because in 1066,
• 14:58
  you had the second best apparition of Comet
• 15:00
  Hallie in the last 2,000 years. Arguably, it
• 15:02
  was very spectacular in the sky at the time
• 15:04
  the conquest was going on. And, um, that was
• 15:06
  considered important enough to be recorded in
• 15:09
  the tapestry that was woven at the time. You
• 15:12
  know, it's amazing that you've got this panel
• 15:14
  where there's all the peasants pointing up at
• 15:16
  this thing in the sky and somebody whispering
• 15:18
  in King Harold's ear about the comet that's
• 15:20
  visible. So, yeah, don't know whether the
• 15:23
  invading forces took it as a good sign or a
• 15:25
  bad sign, but they thought it was important
• 15:27
  enough to include. So that in
• 15:29
  itself is fairly breathtaking. And so when we
• 15:31
  see these objects, it's a lovely connection
• 15:33
  to thousands of years of our heritage of
• 15:36
  people looking at the night sky in wonder I
• 15:39
  think the first step we had really,
• 15:43
  in moving from cultural
• 15:46
  cometary astronomy to modern scientific
• 15:48
  astronomy, in a way, came with the Great
• 15:51
  Comet of 1577, which was
• 15:54
  another of the really amazing, spectacular,
• 15:56
  bright comets that was widely
• 15:59
  observed, hence why it's a great comet.
• 16:02
  But it was observed by the great astronomer
• 16:04
  Tycho Brahe. And, um, I'm sure Brahe is
• 16:07
  featured on the podcast many times before,
• 16:09
  but the quirky individual he was, it's well
• 16:11
  worth looking up. His Wikipedia record is
• 16:14
  this wealthy nobleman with a silver
• 16:17
  replacement nose after he lost half his nose
• 16:19
  in a duel. He's that guy. Yes,
• 16:22
  yes. Um, he had a pet moose that died when it
• 16:24
  fell down the steps because it got drunk at a
• 16:26
  banquet. He really odd, odd
• 16:29
  man. Um, but probably viewed as being
• 16:32
  the last great pre telescope astronaut,
• 16:35
  astronomical observer, if that makes sense.
• 16:36
  Naked eye observer. Now, at this time,
• 16:39
  comets were kind of thought to be probably
• 16:41
  atmospheric phenomenon. They were nearby,
• 16:44
  high in the atmosphere, and so
• 16:47
  that was what was going on. People had that
• 16:49
  kind of idea. He realized that if that were
• 16:52
  true, these things would display a noticeable
• 16:55
  parallax if people observe them from
• 16:57
  different locations. Uh-huh. So in other
• 16:59
  words, people looking from different
• 17:01
  locations would see the comet in a different
• 17:04
  place in the sky because it was in the
• 17:06
  foreground. It's the same technique we use to
• 17:08
  measure the distance to the nearest stars. If
• 17:10
  you put your finger in front of your face and
• 17:12
  look at it through one eye and then look
• 17:13
  through the other, you'll see your finger
• 17:15
  blinking side to side. And the further away
• 17:18
  your finger is, the less it moves. We use
• 17:20
  that to measure the distance to stars by
• 17:22
  observing from one side of the Earth's orbit,
• 17:24
  then the other. But what Brahe did was
• 17:26
  collect observations from around Europe of
• 17:28
  where the comet was in the sky. With those
• 17:31
  observations, he would have been able to
• 17:33
  detect a parallax for the comet if it were
• 17:36
  closer than the orbit of the Moon. So if it
• 17:39
  was atmospheric, absolutely, definitely would
• 17:40
  do. But no measurable parallax was found
• 17:44
  which showed the comet had to be at least a
• 17:45
  couple of million kilometers away. And in
• 17:47
  fact, it was probably several tens of
• 17:49
  millions of kilometers distant. He got this
• 17:52
  beautiful figure, and I've. I use this in my
• 17:54
  talks occasionally. That is his drawing of
• 17:57
  the motion of the comet. And it's fascinating
• 17:59
  from a cultural point of view because it's
• 18:01
  clearly at the time when you still have the
• 18:03
  geocentric model, the Earth was the center of
• 18:05
  the universe. So you've got the Earth in the
• 18:06
  middle, the sun going around the Earth but
• 18:09
  then Mercury, Venus and the moon going around
• 18:11
  the sun. This kind of weird hybrid thing.
• 18:13
  Yeah, but you've got the path of the comet
• 18:15
  moving through there that he's determined.
• 18:17
  And what's really interesting to me, what's
• 18:19
  really fascinating is he's got the tails
• 18:22
  pointing away from the sun all the time. So
• 18:24
  he's got the phenomenology of where the comet
• 18:26
  is in the solar system. Modular.
• 18:30
  The sun's going around the Earth and the
• 18:32
  tails pointing the right way as it moves.
• 18:34
  Tails of comets always pointing away from the
• 18:36
  sun. And to me that kind of marks the
• 18:39
  dawn of the modern scientific view
• 18:42
  of comets from the cultural. We don't
• 18:45
  know what they are, but they are important.
• 18:50
  That's a real kind of boundary point for me.
• 18:52
  Andrew Dunkley: Yeah, yeah, fascinating.
• 18:53
  I was actually going to ask you about the uh,
• 18:55
  you know, the point in time where we went
• 18:57
  from the mythology m to the
• 19:00
  understanding that this, this was something
• 19:03
  else. And yeah, you covered that beautifully.
• 19:05
  Gonna just take a breath on space nuts. Uh,
• 19:08
  you're with Andrew Dunkley and Professor
• 19:10
  Jonti Horner.
• 19:14
  Jonti Horner: 0G and I feel fine. Space nuts.
• 19:17
  Andrew Dunkley: I did say a breath. That was quick.
• 19:18
  Um, let's continue talking about, uh, comets
• 19:21
  and meteors. There have been a lot of them in
• 19:24
  the news of late. Um, Comet
• 19:26
  Pan Stars is, um, you know, it was very,
• 19:29
  very popular, uh, late
• 19:32
  April. Uh, and uh,
• 19:35
  we've seen in recent times, um, a
• 19:38
  new kind of comet. And those are the ones
• 19:40
  that are coming from other systems, uh,
• 19:43
  not the ones that are
• 19:45
  continually rotating through our own solar
• 19:48
  system. We've had these exo comets that have
• 19:52
  been quite intriguing and um,
• 19:54
  opening up all sorts of new ideas and
• 19:56
  questions about, uh, comets and other
• 19:59
  parts of the universe and what we could learn
• 20:02
  from them. Um, and
• 20:05
  new comets are being discovered all the time.
• 20:08
  That doesn't mean they haven't been here
• 20:09
  before, but it does mean that they've got
• 20:12
  very longitudinal travel times.
• 20:15
  So, um, you know, some we won't ever see
• 20:18
  because we'll have been and gone before they
• 20:20
  get here and others we'll
• 20:23
  maybe see several times during our lifetimes.
• 20:26
  Jonti Horner: Absolutely. Now historically, people broke
• 20:29
  the comets we found down into two categories.
• 20:31
  We had short period comets, which are
• 20:34
  comets. The definition when I was a kid was
• 20:36
  comets whose orbital periods were less than
• 20:38
  200 years shorter than that and you were a
• 20:41
  short period comet, longer than that and you
• 20:42
  were a long period comet. Now there are
• 20:44
  subtleties within that, within the short
• 20:46
  period comets. We have comets like Comet
• 20:48
  Hallie, which are called the Hallie type
• 20:49
  comets which come round with a period
• 20:52
  comparable to a human lifetime or a bit
• 20:54
  longer. The two brightest and most famous of
• 20:56
  those are Comet Hallie and Comet Swift
• 20:57
  Tuttle. You then have the Jupiter family
• 20:59
  comets, which are comets whose orbits, uh,
• 21:01
  are just a few years and are typically under
• 21:04
  Jupiter's control. And when I was a kid,
• 21:06
  anything longer than 200 years was considered
• 21:08
  long period. Now that kind of got smashed
• 21:11
  into the ground a bit in the early 2000s when
• 21:13
  Comet IKEA Jang was sighted, because Comet
• 21:16
  Ikea Zhang was very well observed,
• 21:19
  its orbit was well calculated and it was
• 21:20
  found to have a period of 366 years, I think
• 21:23
  it is. And that allowed people to identify
• 21:26
  the previous observations of that comet from
• 21:28
  the last time it was around. So that's
• 21:30
  currently the record holder where we're
• 21:33
  absolutely certain that it's been seen on
• 21:36
  multiple occasions and it has a
• 21:38
  periodic comet designation now. Now a
• 21:41
  subtlety to that is we do have the Kreutz sun
• 21:43
  grazing comets. I can talk more about them a
• 21:45
  little later where we have a strong
• 21:47
  identification between an observation of
• 21:50
  the comet, say with comedy kaya Seki in
• 21:52
  1965 and um, a previous
• 21:55
  apparition in the 1100s, which is about
• 21:58
  an 800 year return. Yeah, that's a bit
• 22:00
  woolier because the comets we observe now are
• 22:03
  fragments of one comet back then, and
• 22:06
  so therefore several comets tied to that
• 22:08
  initial apparition. So there's all that
• 22:09
  complexity there. We then have the long
• 22:12
  period comets, which, like I say were
• 22:14
  200 years or more. It still kind
• 22:17
  of is. But with those objects that are both
• 22:19
  long period and short period thanksgiang,
• 22:22
  you've got these objects whose orbital
• 22:23
  periods are so long that they are markedly
• 22:26
  longer than a human lifetime, even if they're
• 22:28
  comets that have been through before. So a
• 22:30
  good example of a really bright comet that is
• 22:32
  considered long period but has been through
• 22:35
  many times before is Comet Hale Bopp. Yes,
• 22:38
  was spectacular in 96, 97. It was visible
• 22:41
  with a naked eye for 18 months, shattering
• 22:43
  all the records. It will be back in about the
• 22:45
  year 4400. It was the last round when the
• 22:47
  Egyptians were building pyramids. And that is
• 22:50
  perversely a long period comet with a
• 22:53
  relatively short period orbit for a long
• 22:55
  period of comet. And so scientifically we'd
• 22:58
  call that dynamically old or not a
• 23:01
  new comet because it's been around a number
• 23:02
  of times at the very long period
• 23:05
  end of the long period comets, you get things
• 23:07
  that are coming in from halfway to the
• 23:09
  nearest star from a region we describe as the
• 23:12
  Oort Cloud or the Opic Oort cloud. And
• 23:14
  those things on their way in have
• 23:17
  calculated orbital periods of hundreds of
• 23:20
  thousands or even millions of years. And many
• 23:23
  of those actually only come through once. And
• 23:25
  then they get nudged and ejected from the
• 23:27
  solar system, never to return, going out to
• 23:29
  wander among the stars. And it's objects like
• 23:32
  that that will become the interstellar comets
• 23:34
  for other stars, in the same way that
• 23:37
  this third group of comets that you alluded
• 23:38
  to that we found recently are interstellar
• 23:41
  comets in our system. So these are the
• 23:43
  objects coming through so quickly that they
• 23:45
  are not gravitationally bound to the sun,
• 23:47
  but also so quickly that there is no
• 23:49
  possibility that they ever were. They've been
• 23:52
  flung in so quickly that they must come from
• 23:55
  another place. The most recent one was Three
• 23:58
  Eye Atlas, which got talked about a huge
• 24:00
  amount. Yes. Was definitely not an alien
• 24:03
  spaceship. And to avoid getting too
• 24:05
  political, just a very brief comment on that
• 24:07
  because it needs to be stated and restated,
• 24:09
  which is, uh, the arguments of that being an
• 24:12
  alien spaceship were the work of one person.
• 24:15
  One person who is not a solar system
• 24:17
  astronomer historically, but has reached that
• 24:19
  age and level of senility that they believe
• 24:22
  they can be an expert in things that they are
• 24:24
  not and has a certain financial interest in
• 24:27
  keeping people interested in aliens because
• 24:29
  they buy his book.
• 24:31
  Andrew Dunkley: Click.
• 24:32
  Jonti Horner: The community of astronomers has been very
• 24:35
  upset and very Shrek about that because it
• 24:37
  diverts attention from what is a really
• 24:39
  fascinating object on the fact that it's
• 24:41
  really fascinating, but also breeds a certain
• 24:44
  amount of fear. And I genuinely had people
• 24:45
  reaching out to me when he was pushing
• 24:48
  this narrative of it being aliens that were
• 24:50
  going to invade because they were frightened,
• 24:51
  heightened, they were genuinely worried
• 24:54
  because a Harvard astronomer was saying
• 24:55
  aliens were going to come and beat us all up.
• 24:58
  Andrew Dunkley: Yeah.
• 24:59
  Jonti Horner: And it's problematic because it hides the
• 25:01
  science, but it's also more widely
• 25:03
  problematic at a time when we have lowering
• 25:06
  levels of engagement with science and very
• 25:09
  much lowering levels of trust in science and
• 25:11
  scientists. It's very bad to have someone
• 25:14
  acting disingenuously, telling lies
• 25:17
  on muddying the water. Um, and then
• 25:19
  arguing that everybody else is wrong and mean
• 25:21
  to me and I'm the only one telling the truth.
• 25:23
  And it's part of that whole fake news thing
• 25:26
  that I think is dangerous and damaging.
• 25:29
  You know, we need people to have trust and
• 25:32
  faith in science because it's so integral to
• 25:33
  our lives. And it's good to question. But
• 25:36
  it's bad when people say things that they
• 25:38
  fundamentally know are not true just to get
• 25:40
  hits or clicks or money. Yeah.
• 25:43
  Andrew Dunkley: And it's important to debunk that
• 25:46
  kind of, uh, approach because
• 25:49
  I've had people come up to me very recently
• 25:51
  who know I do this podcast, uh,
• 25:54
  who've said to me, oh, what do you think of
• 25:56
  that alien spaceship? And I go, it's,
• 25:59
  it's, that's what I think
• 26:01
  because it's, it's somebody trying to get
• 26:04
  media attention. It's got nothing. It's a
• 26:05
  rock. It's actually, it's, it's a, it's an
• 26:08
  ice conglomerate. It's, it's not a, it's not
• 26:10
  a spaceship at all. It's not behaving like a
• 26:13
  spaceship would. It's behaving like something
• 26:15
  passing through our solar system.
• 26:18
  Um, and people, people. The thing is,
• 26:21
  Jonti, people are buying
• 26:22
  Jonti Horner: this rubbish, but there's an old saying
• 26:25
  that you know, like, and run around the
• 26:28
  world before the truth has got its boots on,
• 26:30
  especially when it's an attractive light.
• 26:32
  It's, I mean, again, digging into my
• 26:35
  memories of Terry Pratchett stuff which
• 26:36
  happens a lot. It's the old quote when
• 26:39
  they're talking about newspapers and nobody
• 26:41
  really ever wants to hear a story about dog
• 26:43
  bites mum because it happens all the time.
• 26:44
  But if you've got a story that says Mum bites
• 26:46
  dog, everybody's fascinated.
• 26:48
  Andrew Dunkley: Yeah.
• 26:48
  Jonti Horner: And this story has all the elements. It's so
• 26:51
  salacious that it gets coverage and people
• 26:53
  who don't normally read or digest science
• 26:56
  are not interested, will see this and hook
• 26:58
  into it. And when the byline is Harvard
• 27:00
  astronomer, that gives it a huge amount of
• 27:03
  credence.
• 27:03
  Andrew Dunkley: It does.
• 27:04
  Jonti Horner: Uh, and nobody hears the rebuttals. It's
• 27:07
  a bit like, you know, when there are claims
• 27:09
  of life on a planet around another star.
• 27:10
  Nobody remembers the, the follow
• 27:13
  ups that say actually it wasn't. They just
• 27:15
  remember, oh, we found aliens and we haven't.
• 27:18
  I mean, I think that story that,
• 27:20
  Andrew Dunkley: uh, the most recent story
• 27:23
  that I recall where that, that claim was made
• 27:26
  was um, the one about the
• 27:29
  something they. What was it they found in
• 27:31
  the, in the atmosphere of Venus. It was
• 27:34
  phosphine.
• 27:34
  Jonti Horner: Yes. I can go on a little bit of a side rant
• 27:37
  about that. My heart broke. Um, the
• 27:39
  lead author on that study was Jane Greaves in
• 27:42
  the uk, who's someone I knew very well when I
• 27:44
  was in the uk and she's a fabulous science
• 27:46
  and just all around wonderful individual. And
• 27:49
  the story was led by a UK team
• 27:52
  who, if you actually read the paper, don't
• 27:54
  say anything that is, this is life. What they
• 27:57
  say is we found a very weak signal of
• 28:00
  this gas in Venus's atmosphere. It's right
• 28:02
  down in the noise. So there is a chance it's
• 28:04
  a false positive anyway, so there needs to be
• 28:07
  a bit of extra work done. It's a little bit
• 28:09
  interesting because on the Earth, the only
• 28:12
  processes that produce this peculiar gas
• 28:15
  are, uh, technology and industry or life.
• 28:19
  Yeah. We don't know of any other way that
• 28:20
  it's made, but that doesn't mean that there
• 28:22
  aren't other ways that it's made.
• 28:23
  Andrew Dunkley: Isn't that a tasty morsel for the popular
• 28:25
  press?
• 28:26
  Jonti Horner: Absolutely.
• 28:26
  But what happened then was that there is an
• 28:29
  American outreach journal,
• 28:32
  um, science communication journal, that broke
• 28:34
  embargo on this story, didn't talk to Jane
• 28:37
  and her colleagues, but instead ran a story
• 28:39
  saying British scientists found life on
• 28:41
  Venus. Which is not what they'd said at all.
• 28:43
  No, that's what started the absolute bum
• 28:45
  fight. And the vitriol on the hair and the
• 28:48
  death threats, believe it or not, that Jane
• 28:50
  Grieves got because of this were
• 28:53
  astonishing. It was absolutely terrible. And
• 28:55
  instead of being able to managed to deploy
• 28:58
  this wonderful story about this fascinating
• 29:00
  new result they got, they spent all their
• 29:02
  time in damage control because this
• 29:06
  publication chose to break the embargo
• 29:08
  early and run a story that was not factually
• 29:11
  true, but again would get them clicks. Yep.
• 29:13
  Andrew Dunkley: Yeah. And that's unfortunately, the modern
• 29:16
  media and, um, the Internet's to
• 29:19
  blame. Well, it's not the Internet that's to
• 29:21
  blame. It's the people who use it that are to
• 29:23
  blame. And it's one of the, um,
• 29:26
  one of the things you've really got to be
• 29:27
  careful of when you are, uh, following
• 29:30
  a story, whether it's an exocomet that's not
• 29:33
  a spaceship or, uh, life that's
• 29:36
  not in Venus's atmosphere,
• 29:38
  um, and even to a lesser
• 29:41
  degree, and you and I mentioned this before
• 29:43
  we started, the way the media gets its
• 29:45
  information confused, such as
• 29:48
  reporting, uh, on, um, upcoming spectacular
• 29:51
  meteor showers that, uh, everyone
• 29:54
  gets excited about and then they realize
• 29:56
  they're on the wrong side of the planet.
• 29:57
  Jonti Horner: Absolutely. And this is a caution I give to
• 30:00
  everybody, both for comets and for meteors
• 30:02
  actually, but particularly for those of us in
• 30:03
  the Southern hemisphere, um, meteor showers
• 30:07
  and comets are things that are best seen
• 30:10
  from some latitudes and not from others. And
• 30:12
  for each comet or for each meteor shower
• 30:13
  that's different. Now, I'll talk later on
• 30:16
  about a newly discovered comet that might be
• 30:18
  very spectacular in late 2028.
• 30:21
  That comet is primarily going to be a
• 30:22
  Southern hemisphere object. So it will
• 30:25
  probably be better for us in Australia and
• 30:26
  New Zealand than it will be for people in the
• 30:28
  UK or the us Just as an example,
• 30:31
  when events are happening that are, uh,
• 30:33
  primarily good for the Northern Hemisphere.
• 30:35
  The Northern Hemisphere has more people and
• 30:36
  more media. And what I've seen happen more
• 30:39
  and more is that, uh, the media in Australia,
• 30:42
  and I know the Australian stuff because
• 30:44
  that's local to us. It's probably just the
• 30:46
  same in New Zealand, South Africa, South
• 30:48
  America, all these other places. But the
• 30:50
  media there will pick up these stories and
• 30:52
  just run them without running
• 30:54
  the sanity filter. So the April
• 30:57
  Lyrids are a really good example of this. But
• 30:59
  a better one is probably the Perseid meteor
• 31:01
  shower in August. Now, it's a little bit of
• 31:03
  background here. When we've got a meteor
• 31:06
  shower, we're getting bits of dust and debris
• 31:08
  hitting the Earth's atmosphere and ablating
• 31:11
  at an altitude of about 80 km. Now,
• 31:14
  ablation is a slightly weird thing. People
• 31:16
  often describe this as burning up, but it's
• 31:18
  not burning up in the sense of a flame being
• 31:20
  lit and a fire burning. It's rather that
• 31:22
  these things push into the atmosphere at
• 31:24
  really high speed, pile the air up in front
• 31:26
  of them, getting the air superheated,
• 31:28
  creating a load of plasma. And the heat from
• 31:30
  that makes and vaporizes the bit of debris.
• 31:33
  So it's not burning up in the traditional
• 31:35
  sense. And anytime you see a meteor, you see
• 31:37
  a shooting star, that's what you're seeing.
• 31:39
  And, uh, the bigger the bit of dust, the
• 31:40
  brighter it will be. The faster it's moving
• 31:43
  at a given size, the more energy it's got. So
• 31:45
  again, the brighter it'll be. Yeah. And you
• 31:47
  see shooting stars on any night of the year,
• 31:50
  typically, uh, three or four an hour in the
• 31:53
  evenings, five or six an hour in the
• 31:55
  mornings, potentially. And that difference is
• 31:57
  just because in the mornings you're facing
• 31:58
  the direction the Earth's moving. So you're
• 32:00
  getting collisions that are head on. So the
• 32:02
  average collision speed is higher. So a grain
• 32:05
  of dust that's the same size will be a bit
• 32:07
  brighter. Therefore, the things that in the
• 32:09
  evening that will be too faint to see become
• 32:11
  visible. So you get a slight increase in the
• 32:13
  rate towards morning. Then in the evening,
• 32:16
  um, it's also you're probably getting a
• 32:17
  slightly increased amount of stuff entering
• 32:19
  the atmosphere because you always see more
• 32:20
  flies hit your windscreen than your air
• 32:22
  windscreen. Same kind of idea. Yeah.
• 32:25
  When we get a meteor shower, what's happening
• 32:27
  is we're passing through the area of
• 32:30
  space where the Earth passes near the orbit
• 32:32
  of either a comet or an asteroid. And
• 32:34
  typically it's a comet. Now, every time a
• 32:36
  comet goes around the sun, that dirty
• 32:39
  snowball or snowy dirt ball gets hot. The
• 32:42
  volatile material on the surface is too hot
• 32:44
  to stay solid, so becomes a gas in a
• 32:47
  process called sublimation. And you get jets
• 32:50
  erupting from the comet, shrouding in gas,
• 32:53
  which is then blown away from the sun to give
• 32:55
  you the tails. Those jets erupting into
• 32:57
  space carry with them dust.
• 33:00
  Now, biggest bits of dust are pushed away so
• 33:03
  gently, they'll fall back to the comet and
• 33:04
  clog it up. And some comets eventually turn
• 33:06
  off because of. This also is the reason most
• 33:08
  comets are only active from a few locations
• 33:11
  on the surface, not uniformly, because most
• 33:13
  of the surface is clogged up and you've just
• 33:15
  got a few active areas where volatile
• 33:17
  material is exposed. Yeah, but that dust
• 33:20
  that's ejected from the comet is ejected with
• 33:22
  speeds measured in meters per second or
• 33:24
  centimetres per second from an object that's
• 33:27
  traveling at a speed measured in tens of
• 33:28
  kilometers a second. So what that means is
• 33:31
  that, uh, that dust is moving away from
• 33:34
  the comet at a speed almost identical to the
• 33:36
  speed the comet's traveling itself. I guess
• 33:39
  it's like if you. You're driving along the
• 33:41
  road and you drop a tennis ball out of the
• 33:43
  window until the wind resistance pushes it
• 33:45
  back. If there wasn't a wind resistance
• 33:47
  there, it would move along with the car, just
• 33:50
  drifting away very slightly based on the
• 33:51
  speed you pushed it out of the window. Same
• 33:53
  idea. Yeah.
• 33:54
  Andrew Dunkley: I actually saw a really great experiment once
• 33:57
  where they were.
• 34:01
  How did they do it? They had a guy on the
• 34:03
  back of a truck, and they
• 34:06
  were driving at, like, uh, 100
• 34:08
  kilometers an hour, and they shot him
• 34:11
  off the truck in the opposite direction at
• 34:14
  the same speed, and he just stopped where he
• 34:17
  landed.
• 34:17
  Jonti Horner: Well, it's brilliant. I think mythbusters did
• 34:19
  something similar, and it's amazing. Our
• 34:22
  common sense is physics, really
• 34:25
  simple physics is great, but our common sense
• 34:27
  breaks down in some situations because our
• 34:30
  common sense is a naturally inherited thing
• 34:32
  about the world at the speeds we experience
• 34:34
  it. And so we tend to think if you're running
• 34:37
  forwards at 10km an hour and you throw
• 34:39
  something forwards, it will travel a bit
• 34:41
  faster. That breaks down when you get to
• 34:43
  relativity. There's all these weird things
• 34:45
  around it where our common sense gets it
• 34:47
  wrong for comets and for the dust. And it
• 34:50
  took me a long while to get my head around
• 34:51
  this because it's a bit counterintuitive if
• 34:54
  you eject Dust from a comet. You can eject
• 34:56
  the dust forward or backwards. So you can
• 34:58
  imagine this jet from the comet working a bit
• 35:00
  like a geyser, turning off when it gets dark
• 35:03
  and it gets cold, and then turning off again
• 35:05
  in the morning when it gets hot again. That
• 35:07
  can throw dust forwards, sidewards, and, um,
• 35:09
  backwards, or any combination of the above.
• 35:12
  So that means this comet is throwing out dust
• 35:14
  at a speed of meters per second, a bit like a
• 35:17
  sprinkler into space. The
• 35:19
  dust has a forward component to its speed.
• 35:22
  So it could be going sideways but a little
• 35:24
  forward, or it could be going head on in
• 35:25
  front of the comet that is now traveling
• 35:28
  around the sun faster than the comet is,
• 35:30
  which means it will move onto, um, an orbit
• 35:32
  with a longer period than the comet. So the
• 35:35
  next time the comet comes round, that grain
• 35:36
  of dust will arrive after the comet. So dust
• 35:39
  thrown forward ends up behind. And similarly,
• 35:42
  dust thrown backwards is moving slower than
• 35:44
  the comet, which puts it on a slightly
• 35:45
  shorter period orbit, and therefore it will
• 35:48
  arrive ahead of the comet next time. And that
• 35:50
  little bit of sidewards motion also means it
• 35:52
  will spread out a little bit in space. What
• 35:54
  this means over, uh, time periods is that,
• 35:57
  uh, comets, every time they come round,
• 35:59
  essentially shed what becomes like a javelin
• 36:01
  shape, a spear of dust into space with a
• 36:04
  comet at the center, like a
• 36:07
  spike. And that spike gradually diffuses over
• 36:09
  time, spreads out further and further ahead
• 36:11
  and behind the comet. And so over a long time
• 36:13
  scale, you eventually end up with the comet's
• 36:16
  orbit shrouded in dust. And the dust can be
• 36:18
  quite spread out over millions of kilometers.
• 36:21
  Yeah, these orbits are oriented randomly in
• 36:23
  space. So many of them don't intersect the
• 36:26
  Earth. Even if the comet gets closer to the
• 36:28
  sun than we are at its closest, passes above
• 36:31
  or below the Earth's orbit, nothing happens.
• 36:33
  But for a subset of them, the comet
• 36:37
  will, in its orbit, have the potential to get
• 36:39
  very close to the Earth. So its orbit and the
• 36:41
  Earth get very close together. And in those
• 36:43
  cases, every time we go around the sun, if
• 36:46
  that comet's been laying dust down for a
• 36:47
  while, we'll run into the dust every time we
• 36:50
  go around. And that dust will hit the Earth's
• 36:52
  M atmosphere, which means we're going through
• 36:54
  a dirtier bit of the solar system and we get
• 36:56
  more meteors. That's when we get a meteor
• 36:58
  shower. But the other telltale thing for the
• 37:00
  meteor shower is all the dust grains that hit
• 37:03
  the Earth in a meteor shower are moving
• 37:05
  essentially parallel to each other.
• 37:07
  They're all following the same Orbit around
• 37:08
  the sun, hitting the Earth, the Earth from
• 37:09
  the same direction at the same speed.
• 37:13
  So all this dust is coming towards you from a
• 37:15
  single point in space. So from your point of
• 37:17
  view, looking at the sky, when you see those
• 37:19
  meteors, part of a meteor shower, they appear
• 37:22
  to appear anywhere in the sky. But if
• 37:25
  you trace them back, they'll all point to a
• 37:26
  single point in the sky, that something we
• 37:28
  call the radiant. And that's effectively the
• 37:31
  point in space they're traveling towards us
• 37:33
  from. And um, they diverge because they
• 37:35
  perspective, they're coming closer to you. So
• 37:37
  every meteor shower has a radiant in the sky.
• 37:40
  The April Lyrids have their radiant in
• 37:43
  Lyra, although for a fair part of their time
• 37:45
  it's actually in Hercules, it m drifts a bit.
• 37:47
  The Perseids have their radiant in Perseus,
• 37:50
  the Geminids in Gemini and so on.
• 37:53
  So that's all well and good. If the
• 37:56
  radiant is below the horizon, that means the
• 37:59
  meteors are hitting the other side of the
• 38:00
  Earth and you can't see them because the
• 38:02
  Earth's in the way. So first point with a
• 38:04
  meteor shower is unlike some of the media
• 38:07
  reports, you can't see meteors for that
• 38:09
  meteor shower at any time of night. You can
• 38:12
  only see them when the radiance above the
• 38:13
  horizon point, number one
• 38:16
  point. The second is the higher in the sky
• 38:18
  that radiant is, the more head on into the
• 38:21
  stream you're going. So the more meteors
• 38:23
  you'll see. Now the analogy I'd ah, use here
• 38:26
  is if you imagine getting your hose pipe and
• 38:28
  having it on that shower mode, you know,
• 38:30
  where water's coming out from many holes all
• 38:32
  at once. If you hold that hose pipe
• 38:35
  vertically and turn the tap on, all the water
• 38:37
  from that hose pipe will hit a relatively
• 38:38
  small area of the ground. If you turn that
• 38:41
  hose pipe to 45 degrees, that water will
• 38:44
  spread out over a larger surface area.
• 38:47
  Andrew Dunkley: Yep.
• 38:47
  Jonti Horner: Now if you imagine the meteors, the dust in a
• 38:49
  meteor shower coming in towards the Earth,
• 38:52
  the more directly overhead
• 38:54
  your point that they're coming from is the
• 38:57
  more meteors you'll get in a certain volume
• 38:59
  of the atmosphere and the lower to the
• 39:01
  horizon that point is, the more you'll spread
• 39:03
  those same number of grains of dust out.
• 39:06
  So the higher in the sky the radiant is, the
• 39:09
  more dust is hitting the part of the
• 39:10
  atmosphere you can see from your location. So
• 39:13
  the more meteors you get, and what this means
• 39:15
  is that the lower in the sky the rating is a
• 39:17
  few meteors you see. And so you see the most
• 39:20
  Meteors. For a given meteor shower, when the
• 39:22
  radiant is near what we call culmination,
• 39:24
  where it's nearly highest in the sky. For the
• 39:26
  southern hemisphere, when it's nearly due
• 39:28
  north, for the northern hemisphere rain, the
• 39:31
  radiant's nearly due south. So
• 39:33
  all well and good, but what that means is
• 39:36
  that ah, from different locations on the
• 39:38
  earth, a given meteor shower will give you a
• 39:40
  different strength of display. The April
• 39:42
  Lyrids, their radiant is
• 39:46
  34 degrees north of the equator. So that
• 39:48
  means if you lived 34 degrees north of the
• 39:50
  equator at about 2am in the morning, the
• 39:53
  radiant will be overhead and you're in the
• 39:55
  best place on the planet to see the meteors.
• 39:57
  If you had perfect vision, perfectly dark
• 40:00
  sky, you'd see a number of meteors, 15
• 40:03
  to 20 per hour for the April Lyrids and
• 40:05
  that's called the zenithal hourly rate.
• 40:07
  That's the number of meters you'd see in
• 40:09
  perfect conditions with perfect eyesight,
• 40:11
  with no light pollution if the radiant was
• 40:13
  overhead. The lower the radiant is in the
• 40:16
  sky, the more that number shrinks. So the
• 40:18
  ZHR is the theoretical maximum number
• 40:21
  you'd see. So good
• 40:23
  meteor shower, not a great one from the
• 40:25
  northern hemisphere, but for us in Brisbane,
• 40:27
  let's say 26 degrees south.
• 40:30
  The radiant of the April Lyrids at its
• 40:32
  highest in the sky is only 30 degrees above
• 40:34
  the horizon. That means that the
• 40:37
  volume of space where the dust is arriving is
• 40:40
  doubled. So you'd only see half the number of
• 40:42
  meteors. So instead of 20 per
• 40:45
  hour, you're down to 10 an hour
• 40:47
  immediately before anything else kicks in.
• 40:50
  And the further south you go, the lower the
• 40:52
  rates are. But the problem is the journalists
• 40:55
  covering this will pick up on a Northern
• 40:56
  hemisphere article and just repeat it.
• 40:58
  There's this meteor shower happening. You can
• 41:00
  see them all night, every night. Well that's
• 41:02
  not right. If the radiance below the horizon,
• 41:04
  you can't see them and you'll see 100 per
• 41:06
  hour and M that's because they've seen the
• 41:08
  zenithal hourly rate, quoted as 100 per hour.
• 41:10
  And they just use it as a number.
• 41:12
  Andrew Dunkley: Yeah.
• 41:13
  Jonti Horner: Unless you are incredibly, incredibly
• 41:15
  fortunate, you will never see the same number
• 41:18
  of meteors as the ZHR predicts
• 41:21
  because the radiant might be directly
• 41:23
  overhead. So the rate gets lower. Your eyes
• 41:25
  are not perfect unless you're one of the very
• 41:27
  rare observers. The rates will get lower,
• 41:30
  there might be light pollution. The phantom
• 41:33
  meteors are not seen, the rates get lower.
• 41:35
  The moon might be in the sky. The phantom
• 41:37
  meters are not seen. The rates are lower. So
• 41:40
  you will never see a number of meteors in the
• 41:42
  sky equal to the ZHR unless the meteor
• 41:45
  shower is more active than predicted in which
• 41:48
  case the ZHR will be higher and you'd see
• 41:49
  more. Where this really comes in is for
• 41:52
  meteor showers like the Perseids. The
• 41:54
  Perseids are one of the big three. There are
• 41:56
  AH3 awesome meteor showers a year that are by
• 41:59
  far the best in a given year.
• 42:01
  They're the highest rates, the most dust
• 42:04
  coming in. Other high speed, the Quadrantids
• 42:06
  in early January are very, very short
• 42:09
  lived. They're a wage shower. You've got a
• 42:11
  very low rate of meteors for most of the time
• 42:13
  they're active and then a very narrow spike
• 42:14
  that can be very big. But if you manage
• 42:17
  to see that spike there's a lot of meteors.
• 42:19
  They're only really visible from the northern
• 42:21
  hemisphere. The Perseids in August are
• 42:24
  probably uh, the most storied meteor shower
• 42:27
  with long history of observations
• 42:31
  linked to comet Swift Tuttle which goes
• 42:32
  around every 120. 130 years
• 42:35
  incidentally will be incredibly spectacular
• 42:37
  in the year 2126 if people hang around to see
• 42:39
  it.
• 42:40
  Andrew Dunkley: Yeah, okay, I'll write that in my diary.
• 42:43
  Jonti Horner: Um, Perseids are brilliant but their radiant
• 42:45
  is at about 55 degrees north in the sky.
• 42:49
  Fabulous from northern Europe, fabulous from
• 42:51
  North America, places north of the equator to
• 42:53
  get a really good show. But we get articles
• 42:55
  every year on commercial media here in
• 42:58
  Australia saying the persons are happening go
• 43:00
  up tonight and you'll see 100 meters an hour.
• 43:02
  And for most of Australia the radiant never
• 43:04
  even rises, never, you know, south of about
• 43:07
  35 degrees south the radiant will never rise.
• 43:10
  I think that's about the latitude of Sydney.
• 43:13
  North of that it will rise but it'll be very
• 43:15
  low to the horizon. So you'll see a much
• 43:16
  lower rate unless you're in the top, top end.
• 43:19
  If you're in the top end of Australia it's a
• 43:20
  bit different. And so when you see
• 43:23
  articles like this you need to engage
• 43:26
  your science brain and say the journalist
• 43:28
  wrong. Yeah, where's my location?
• 43:30
  What's the radiance? Declination which
• 43:33
  is latitude in the sky effectively figure out
• 43:36
  how high in the sky it'll get and that will
• 43:38
  give you a feel for what you might actually
• 43:39
  see. Now if you want to um, look
• 43:42
  at the meteor shower calendar and figure out
• 43:44
  when there are good ones happening, the
• 43:46
  International Meteor Organization is my go to
• 43:48
  on this. They're a fabulous organization that
• 43:51
  put together every year a calendar and that
• 43:53
  calendar lists all the meteor showers from
• 43:55
  the incredibly minor ones that give one
• 43:57
  meteor every two hours, you know, to the
• 43:59
  major ones. And every year it writes about
• 44:02
  the conditions in terms of moonlight as well.
• 44:05
  Because if the moon is bright, you will see
• 44:08
  far fewer meteors. And coming up in a couple
• 44:11
  of weeks from when we're having this
• 44:13
  discussion, but in the past, as we actually
• 44:15
  go live to air, you've got the peak of the
• 44:17
  Ytraquarids. Now the Yter Aquarids are one of
• 44:19
  the few showers that's better for Southern
• 44:21
  hemisphere than Northern Hemisphere
• 44:22
  hemisphere. Fragments of Comet Hallie, and
• 44:24
  they're at their peak around the 3rd to the
• 44:26
  7th may have quite a broad peak, but
• 44:29
  this year the moon is a waning
• 44:32
  gibbous. So at the time of night when you
• 44:34
  could see these meteors, the sky will be
• 44:36
  really bright and so far fewer will be
• 44:38
  visible than normal. And you can get that
• 44:41
  from these calendars. But the highlight of
• 44:42
  every year for meteor showers is the Geminids
• 44:45
  in December. And they are pretty much global
• 44:48
  as a phenomenon and they're brilliant
• 44:50
  everywhere. Obviously better for the Northern
• 44:52
  hemisphere than the south. That's like a
• 44:53
  recurring theme, but
• 44:56
  they are great every year. And this year,
• 44:59
  Moon will be effectively new. So if you want
• 45:01
  to go see the Geminids peaking on the 14th or
• 45:03
  15th of December, they're the highlight this
• 45:06
  year and pretty much every year.
• 45:08
  Andrew Dunkley: Okay, uh, we're going to take another breath
• 45:10
  and then we'll come back and wrap it all up
• 45:12
  in this episode of Space Nuts with Andrew
• 45:14
  Dunkley and Jonti Horner.
• 45:20
  Jonti Horner: Tranquility Base here.
• 45:21
  Andrew Dunkley: The eagle has landed.
• 45:23
  Jonti Horner: Space gnats.
• 45:24
  Andrew Dunkley: One of my big frustrations, uh,
• 45:27
  when I want to observe comets is I live on a
• 45:29
  very flat area of the planet. Uh,
• 45:32
  we don't have mountains nearby, we barely
• 45:35
  have hills. And a lot of the comets
• 45:38
  are visible, uh, in the low
• 45:41
  horizon just after sunset or
• 45:45
  thereabouts. And they're short lived
• 45:48
  and they're below the horizon way too
• 45:51
  quick. Uh, which makes astrophotography a
• 45:53
  real pain in the butt for me. But it is
• 45:57
  just a quirk of where I live.
• 45:59
  Um, I believe
• 46:02
  that we do have some pretty spectacular ones
• 46:05
  coming up. The one that I've seen
• 46:08
  in my life that was the most spectacular for
• 46:11
  me was in 2007, January
• 46:13
  2007. Uh, the, it
• 46:16
  was Comet McNaught. It was amazing,
• 46:19
  like naked eye, comet wise. It
• 46:22
  was unmissable. Uh, it dominated
• 46:25
  the sky for quite some time. Uh, we don't see
• 46:28
  many like that though, do we?
• 46:30
  Jonti Horner: We don't now. Comet McNaught was probably the
• 46:32
  brightest comet since the 1960s and it was
• 46:35
  truly a great comet. Now when we talk
• 46:37
  about the brightest comets and the ones
• 46:40
  people want to see, great comet is the
• 46:42
  Appalachian people attached to comets. And
• 46:44
  it's got a woolly ish definition. It's
• 46:46
  basically the comet was bright enough and
• 46:48
  spectacular enough that even people who
• 46:50
  weren't that interested could just step
• 46:51
  outside and see it. Comet McNaughts
• 46:53
  definitely like that. Arguably Comet Chichin
• 46:56
  Chan Atlas in 2024 and Comet Atlas in
• 46:59
  early 2025 just made that threshold.
• 47:02
  So if you saw those comets, you'd probably
• 47:04
  say they are right at the lower end of what
• 47:07
  we consider a great comet. On average,
• 47:10
  if you go back through historical comic
• 47:12
  records, you'd probably get about 10 great
• 47:14
  comets per century with very wide
• 47:17
  variants. And that's not one every 10 years.
• 47:20
  They're like buses. You wait 30 years and two
• 47:22
  come along at once. And you saw that back in
• 47:24
  1996 with Comet Hale Bop and Comet Hyakitake,
• 47:27
  which were visible in the sky at the same
• 47:29
  time as great comets. It's really
• 47:32
  hard to predict when they're going to come
• 47:33
  in. But we've seen some really fascinating
• 47:35
  advances in the last few years on two fronts.
• 47:38
  Firstly, our ability to find things
• 47:41
  early has improved. We've got better
• 47:43
  telescopes, more automated surveys, and,
• 47:46
  um, comet maps earlier this year, which
• 47:48
  turned out to be a bit of a disappointment
• 47:49
  for many people, is a really good example of
• 47:51
  that. That's a member of the Kreutz
• 47:53
  sungrazing family. And the Kreuz sungrazers
• 47:56
  have numbered many of the brightest great
• 47:58
  comets of the last couple of thousand years.
• 48:01
  Comet maps was the earliest we've ever found
• 48:03
  a Kreutz sungrazer on the way in, earlier
• 48:06
  even than Comedike Oseci, which was probably
• 48:09
  the brightest comet in the 20th century back
• 48:11
  in the late 1960s. And so people's hopes were
• 48:14
  high. But in reality it was quite a small
• 48:16
  fragment of the Kreutz parents
• 48:19
  sungrazer. These Kreutz comets are all
• 48:20
  fragments of a bigger comet in the past, and
• 48:23
  it just fell apart on its way in. Nothing to
• 48:25
  see here. But our ability to find
• 48:28
  things earlier means that we get more
• 48:30
  warning when a bright comet's coming. Now
• 48:32
  that's not absolutely guaranteed. We had a
• 48:35
  comet and the name of it slipped my mind. Um,
• 48:37
  Comet 12, 18 months ago. Um, no,
• 48:40
  I think it was like last September
• 48:44
  that was discovered when it was almost naked
• 48:46
  eye visibility. It just about became naked
• 48:49
  eye visible wasn't great by any means. Swan.
• 48:51
  We got no warning. That's it, Comet Swan. And
• 48:54
  the reason that that was found so late was it
• 48:56
  came at us from behind the sun and suddenly
• 48:58
  popped into view. So that does still happen,
• 49:01
  but with facilities like Vera Rubin coming
• 49:04
  online, we're going to find comets earlier
• 49:05
  and earlier, which means we get more prior
• 49:08
  warning. But it also means that the
• 49:10
  uncertainty about how bright they're going to
• 49:12
  get is possibly even higher because we're
• 49:13
  almost finding them now before they've really
• 49:16
  started to become active. While they're far
• 49:18
  enough from the sun that we're almost seeing
• 49:19
  a bare nuclear nucleus, or we're seeing
• 49:22
  a much smaller comet that's had a little bit
• 49:24
  of an outburst at that distance and whether
• 49:26
  that far away, we effectively can't tell the
• 49:28
  difference. They're still like a single
• 49:30
  pixel. There's a really good example of this
• 49:32
  in the form of Comet Chu Chin Shan. Um,
• 49:35
  not come to Chin Chan ATLAS from a couple of
• 49:37
  years ago, but Comet Chu Chin Shan that has
• 49:38
  just been discovered in the last couple of
• 49:40
  months, Comet C 2026
• 49:42
  C1. As we record this, that
• 49:45
  comet is still more distant from the sun than
• 49:48
  the orbit of Saturn. It was found a couple of
• 49:50
  months ago. It will not be at its closest to
• 49:52
  some perihelion until November
• 49:55
  2028. So we've got two and a half years to
• 49:57
  wait. Now, what factors
• 50:00
  into a comet's brightness is very
• 50:01
  complicated. Um, but it can boil down to a
• 50:04
  few different things. Firstly, if everything
• 50:06
  else is equal. So imagine we only change one
• 50:09
  thing. Typically, the bigger the nucleus of
• 50:11
  the comet, the bigger its surface area is. So
• 50:14
  the more dust and gas it can produce. And we
• 50:17
  see the comet from the light that is
• 50:19
  reflected from the dust and gas. That's what
• 50:21
  makes the tails and the coma. The snowballs,
• 50:23
  ah, at the head were actually pretty small.
• 50:24
  Comet McNaught was only about 5km across
• 50:27
  for the nucleus, but it grew tails more than
• 50:30
  300 million kilometers long.
• 50:32
  Andrew Dunkley: Yeah, that's a little bit different.
• 50:33
  Incredible.
• 50:34
  Jonti Horner: So if you have two cometary nuclei that, uh,
• 50:36
  are in all senses identical other than their
• 50:39
  size, the bigger one will typically be more
• 50:41
  active and produce more gas and dust.
• 50:44
  However, some comets have a m larger fraction
• 50:47
  of their surface active than others. Some
• 50:49
  comets are almost dormant because they're
• 50:51
  clogged up and there's very little activity
• 50:53
  even from a larger nucleus. So already a bit
• 50:55
  complex. But first rule of thumb, um, the
• 50:58
  bigger the nucleus, the more likelihood there
• 50:59
  is that it will be able to produce a lot of
• 51:01
  gas and Dust and be more spectacular. With
• 51:03
  Comet Chu Chen Shan, that's interesting. We
• 51:06
  found it so far away, which suggests it is
• 51:08
  either a comet with quite a large nucleus,
• 51:10
  because it's probably not that active at that
• 51:12
  distance, but it may have just had a bit of
• 51:15
  an outburst of activity driven by something
• 51:17
  like carbon monoxide, which can turn from
• 51:20
  solid gas at a very low temperature. So it
• 51:22
  might be masquerading as a bigger comet than
• 51:24
  it is, and we don't know.
• 51:26
  Andrew Dunkley: Okay.
• 51:27
  Jonti Horner: The next thing that factors into how bright a
• 51:29
  comet gets is how close it gets to the Sun.
• 51:30
  So the closer it gets to the sun, the hotter
• 51:33
  its surface gets and the more strongly it
• 51:35
  will be active. So with Comet McNaught, you
• 51:38
  had a five kilometer nucleus, which is fairly
• 51:40
  respectable, but not as big as Hale Bopp,
• 51:42
  which was 50km. Hale Bok was ridiculous.
• 51:45
  But Comet McNaught got very close into the
• 51:48
  Sun. Um, so it got really incredibly
• 51:50
  intensely active, was throwing off huge
• 51:52
  amounts of gas and dust. So that contributed
• 51:55
  again to more stuff to reflect sunlight. And
• 51:57
  also being nearer to the sun, the intensity
• 51:59
  of light reflecting off its higher as well.
• 52:01
  So kind of get a double whammy there. The
• 52:03
  other factor is how close they get to the
• 52:05
  Earth. So if you have two comets that are the
• 52:07
  same size and the same distance from the sun,
• 52:10
  and, um, one is closer to the Earth than the
• 52:11
  other, the one closer to the Earth will be
• 52:13
  brighter, but will also potentially be more
• 52:15
  spread out and more diffuse in the sky. So
• 52:17
  that brightness might be spread over a
• 52:19
  different area. You've then got
• 52:21
  subtleties of how dusty or gassy they are.
• 52:24
  Some comets, like Comet Pan, stars seem
• 52:27
  to be more gassy. Some comets like Church and
• 52:29
  Chan Atlas was more dusty. And that can have
• 52:31
  an impact on how they brighten. Bringing all
• 52:33
  this back together, though, for Comet Chu
• 52:35
  Chin Chan, at its closest to the sun,
• 52:38
  it will be a little bit further from the sun
• 52:40
  than the Earth, uh, is. So it's not like
• 52:41
  Comet McNaught that's going to get really
• 52:43
  close in. But one AU from the Sun's fairly
• 52:46
  respectable. It can still maintain a fairly
• 52:48
  decent level of activity at that distance.
• 52:49
  Comet Hale Bopp didn't get much closer than
• 52:51
  that and was fantastic. So that's in its
• 52:54
  favorite. It's going to get close enough in
• 52:56
  that you could get a decent level of
• 52:58
  activity. Also, because
• 53:01
  it's only going to get that close to the sun,
• 53:03
  it'll take a bit longer to pass through the
• 53:04
  inner solar system. Comets that get really
• 53:06
  close to the sun get traveling incredibly
• 53:08
  quickly at that point. So they tend to whip
• 53:10
  in and whip out fairly quickly. Whereas with
• 53:11
  cometary chinchan, it's going to hang around
• 53:14
  for a fair while. It is
• 53:16
  potentially quite a large cometary nucleus,
• 53:19
  but we don't know yet. This is the caution I
• 53:22
  give. If it turns out that we've caught it
• 53:24
  during an outburst, it may be a bit of a
• 53:25
  disappointment. If we've actually seen it as
• 53:27
  a bare nucleus. That augurs very, very
• 53:31
  well. What this all suggests is that Comet
• 53:33
  Chichin Shan, um, has a potential to be
• 53:35
  bright in late 2028.
• 53:38
  Depending on which fit to its current
• 53:40
  brightness you use. It could become barely
• 53:43
  naked eye visible, which is still pretty
• 53:45
  good. You know, we see 20 or 30 comets a year
• 53:48
  and very, uh, only maybe one will get to
• 53:50
  naked eye visibility. Or it could get as
• 53:52
  bright as the brightest stars. And if it gets
• 53:54
  as bright as the brightest stars, then it
• 53:56
  gets into great comet type territory.
• 53:59
  That's a factor of 100 difference in
• 54:01
  brightness between those two extremes. And,
• 54:03
  um, it could get brighter than the brightest
• 54:05
  extreme there or fainter than the faintest
• 54:06
  extreme. We just don't know yet. But having
• 54:09
  found it so early augurs well. But typically,
• 54:12
  predicting the next great comet is a fool's
• 54:14
  bargain until it's discovered. What we can
• 54:17
  say is that there are a few periodic comets
• 54:20
  that will be great in the future. Comet
• 54:23
  Hallie will be a lot better in 2061 than it
• 54:25
  was in 1986. In 1986, we had the
• 54:28
  worst separation of Comet Hallie for 2,000
• 54:30
  years.
• 54:30
  Andrew Dunkley: Tell me about it.
• 54:31
  Jonti Horner: Yeah, a bit disappointing. 2071
• 54:34
  will be better.
• 54:35
  Andrew Dunkley: Oh, good. I don't know if I'll be around by
• 54:38
  then, but, um, probably not.
• 54:40
  Jonti Horner: I'll be 99, make everybody
• 54:43
  feel really cheerful. It's now closer to
• 54:45
  Comet Hallie's next apparition than the last
• 54:47
  one. It turned around, I think, last year. So
• 54:49
  it's on its way back. Yeah, Comet Hallie will
• 54:51
  be even better in 21:35, will
• 54:54
  be really good that year. And that will be
• 54:55
  the best apparition for a couple of hundred
• 54:57
  years. Comet Swift Tuttle will be incredible
• 55:00
  in 21:26. We know that because we know pretty
• 55:02
  much exactly when it'll come back. We know
• 55:03
  where it will be compared to the Earth and
• 55:05
  the Sun. There is a suggestion that in
• 55:07
  2097 we may have the comet of the century, or
• 55:10
  close to it. This is research that came out
• 55:12
  last year. One of the greatest comets of the
• 55:15
  last thousand years was Comet De chezo, uh,
• 55:18
  in 1744, also called Comet
• 55:21
  Clinkenberg comet that is famous for having
• 55:23
  had six tails, incredibly bright, almost
• 55:26
  visible in broad daylight. A couple of
• 55:28
  astronomers, I think the lead researcher on
• 55:30
  this was Mike Meyer, published a paper last
• 55:33
  year that went back through historical
• 55:35
  observations and found a number of previous
• 55:38
  comets over the last 2,000 years that were
• 55:40
  all incredibly bright, really spectacular,
• 55:43
  but seem to have been moving the same as that
• 55:45
  comet. Linked them together and it's a very
• 55:47
  compelling tale that if their research is
• 55:50
  correct, that comet actually has an orbital
• 55:52
  period of just a little bit less. Just around
• 55:55
  450 years, I think. 400 years?
• 55:57
  No, 350 years. Wouldn't it do the mental
• 56:00
  arithmetic? Yeah, about 350 years,
• 56:03
  which means it should return in 2097.
• 56:06
  And if it does, it will be awesome.
• 56:09
  Um, sadly I don't think you or I will be
• 56:11
  around for that.
• 56:12
  Andrew Dunkley: Probably not, probably not.
• 56:14
  Jonti Horner: But things like that we can predict. But most
• 56:16
  Fred will be. But um, absolutely, Fred is
• 56:18
  indestructible and I'll stand um, by that.
• 56:21
  But most of the big cometary nuclei coming
• 56:23
  through are on such long period orbits, with
• 56:26
  the exception of Hallie and Swift Tuttle,
• 56:28
  that their apparitions are so infrequent that
• 56:30
  we've not identified them as periodic
• 56:32
  visitors. And many of them have periods of
• 56:34
  thousands or tens of thousands of years. So
• 56:37
  we typically only find them on their way in a
• 56:39
  few weeks or a few months before
• 56:42
  apparition. In case of Comet Hale Bopp, it
• 56:44
  was two years, which was exceptional at the
• 56:47
  time. Case of Comet Chichin Shan, it's more
• 56:49
  than two and a half years away, but our
• 56:51
  technology has improved hugely. So I don't
• 56:54
  think it's fair necessarily to say that
• 56:56
  Church and Chan will be another hell bop. But
• 56:59
  if you look at the brighter end of the
• 57:01
  predictions, it could be naked eye visible
• 57:02
  for three, four, five months.
• 57:04
  Andrew Dunkley: Wow.
• 57:04
  Jonti Horner: Would be awesome. And it would potentially be
• 57:06
  circumpolar for us in the Southern Hemisphere
• 57:08
  because at its closest to the center of the
• 57:10
  Earth, it's going to be way south, not going
• 57:12
  to be good for the Northern Hemisphere. But
• 57:15
  we can't really predict that. It's the same
• 57:16
  with meteor showers. We can predict the
• 57:18
  annual ones roughly how good they're going to
• 57:20
  be. And if you go back to when I was a
• 57:23
  kid, we couldn't really predict meteor
• 57:25
  storms, meteor outbursts, and that's one of
• 57:27
  the things people really love to see. So
• 57:28
  Geminids are great Northern Hemisphere,
• 57:30
  you'll see maybe even 80 or 100 an hour at
• 57:33
  their peak in the early hours of the morning.
• 57:35
  I've seen 50 an hour from our latitude near
• 57:37
  Brisbane.
• 57:38
  They're really good. But what people really
• 57:40
  want to see are meteor storms and they're
• 57:42
  much rarer. There's a few amazing ones.
• 57:45
  Historically. There was one in
• 57:47
  1833 that was linked to the Leonid meteor
• 57:50
  shower that had a rate in excess
• 57:53
  of a hundred thousand an hour, was best seen
• 57:56
  from the contiguous US and
• 57:59
  um, it was bright enough. There were
• 58:01
  sufficient meteors in the sky that miners in
• 58:04
  the US were woken from their campsites
• 58:07
  by the light shining through their tents. And
• 58:09
  people were convinced that the end times had
• 58:11
  come. The Apocalypse was here because he were
• 58:14
  getting as many as 20 meteors per second.
• 58:17
  Andrew Dunkley: Incredible.
• 58:17
  Jonti Horner: Um, now that in the way that kind of Tycho's
• 58:20
  observations in 1577 were probably the birth
• 58:23
  of modern cometary astronomy.
• 58:25
  1833, I think was possibly the birth of
• 58:28
  modern meteor astronomy. Because there'd been
• 58:30
  a storm from the Leonidas in 1799. People
• 58:33
  predicted that there might be another one in
• 58:35
  1866 because maybe this was happening every
• 58:37
  33 years when the comet came back. And indeed
• 58:40
  that happened in 1866.
• 58:43
  And so that was a bit like the birth of
• 58:45
  modern meteor science. And after that people
• 58:48
  said, well, there'll be one in 1899 and there
• 58:50
  wasn't. So that then tripped people up.
• 58:52
  So thanks to that we've gradually developed
• 58:55
  a better understanding of the physics of how
• 58:57
  meteor showers work. And I'm aware time is
• 59:00
  running away from us, but for people
• 59:02
  interested in this, in the run up to, uh, the
• 59:05
  heavily activity in 1999 through to
• 59:08
  2002, there was some amazing research
• 59:11
  done by um, David Asher
• 59:13
  from Amar Observatory and I think fondly on
• 59:16
  David because he was a lovely mentor to me
• 59:18
  when I visited Armagh in 1999. Very
• 59:20
  quiet guy, but incredibly talented
• 59:22
  scientists. And he did this remarkable
• 59:25
  work making predictions of when we would
• 59:28
  and wouldn't get Leonid storms by
• 59:31
  modeling the ejection of dust from the
• 59:33
  cometary nucleus and evolving the dust
• 59:35
  forward in time and go back. Way earlier on I
• 59:38
  mentioned these javelin spikes.
• 59:41
  He effectively modelled those and figured out
• 59:43
  where the spikes will be in a slight nudge up
• 59:45
  or down means that, uh, the Earth will run
• 59:47
  through the spike or not. And the great
• 59:48
  Leonid storms are produced by dust left
• 59:51
  behind just one or two revolutions ago. So
• 59:54
  the activity between 1999 and
• 59:56
  2002 resulted from a few different
• 59:59
  streams. The older they are, the more diffuse
• 1:00:02
  they get. But now we have the ability for
• 1:00:04
  comets we know well and meteor showers we
• 1:00:06
  know well to figure out where those spikes
• 1:00:08
  are roughly going to be how long they are
• 1:00:10
  and, uh, make predictions going forward. Now,
• 1:00:13
  there aren't any great meteor storms
• 1:00:15
  predicted in the relatively near future. The
• 1:00:17
  Leonids are not likely to give major storms
• 1:00:19
  in 2033 or 2066, but will give
• 1:00:22
  increased activity. The reason for that is
• 1:00:25
  Jupiter and Saturn are pulling those javelins
• 1:00:27
  around and making them miss the Earth.
• 1:00:30
  The leanings will probably return in force
• 1:00:32
  in, I think, 2097 with the possibility of a
• 1:00:35
  storm of like 20,000 an hour. But
• 1:00:38
  we're getting to understand that. So with
• 1:00:40
  meteor showers, we can predict the annual
• 1:00:42
  showers. They're very reliable. They
• 1:00:45
  gradually get better and worse with time as
• 1:00:46
  the streams move around and we intersect more
• 1:00:49
  of the material or less. But they're pretty
• 1:00:51
  reliable. Outbursts are harder
• 1:00:54
  to predict, but we're getting better at doing
• 1:00:56
  it. But predicting an
• 1:00:59
  outburst from a shower we've never seen
• 1:01:00
  before or a shower that's incredibly rare,
• 1:01:03
  we typically can't do until it happens
• 1:01:06
  because we need to have a feel for what it's
• 1:01:08
  done in the past. So we occasionally will get
• 1:01:10
  an outburst of a meteor shower we've never
• 1:01:12
  seen before. And you can't predict that. And
• 1:01:15
  that's when it's really exciting because then
• 1:01:17
  you can start to learn about a new meteor
• 1:01:19
  shower being born. You can learn about the
• 1:01:21
  comet that birthed it. It put all that
• 1:01:23
  together. And, um, that's one of the things
• 1:01:24
  where I'll go out and I love my meteor
• 1:01:26
  showers. I'll sit out under the sky and watch
• 1:01:28
  them. But I would love to just be outside
• 1:01:30
  when there's an unexpected outburst, when we
• 1:01:31
  see something new like a meteor shower being
• 1:01:33
  born for the first time.
• 1:01:35
  Andrew Dunkley: And, and that's what we recommend to all our
• 1:01:38
  Spacenads listeners. Uh, get up at 2 o' clock
• 1:01:40
  every morning, every day and go
• 1:01:43
  out and just wait and, you know, one day
• 1:01:45
  you'll get lucky. Might take 20 years, but it
• 1:01:48
  doesn't
• 1:01:48
  Jonti Horner: have to be 2:00am I mean, there is a little
• 1:01:51
  bit of a preference for meteor showers to be
• 1:01:53
  more active in the morning hours, in the
• 1:01:56
  evening hours. But that's purely a geometry
• 1:01:57
  thing. It's linked a little bit to the
• 1:01:59
  direction of the Earth's motion and the
• 1:02:01
  direction things are crossing the Earth's
• 1:02:02
  orbit in that if you think about something
• 1:02:04
  crossing the Earth's orbit at right angles to
• 1:02:07
  the Earth because the Earth's Moving forward
• 1:02:09
  at 30km a second, the direction you would see
• 1:02:12
  that coming from is actually a bit ahead of
• 1:02:14
  you because you've got the addition of the,
• 1:02:15
  the speed the debris is going on the speed
• 1:02:17
  the Earth's moving. So meteor showers
• 1:02:21
  that are uh, visible with radiance that will
• 1:02:24
  be in the morning sky, you've got a little
• 1:02:26
  bit of an additive effect between the speed
• 1:02:27
  the debris is going and the speed the Earth's
• 1:02:29
  moving, which means the average impact speed
• 1:02:32
  of the debris is higher and you get more
• 1:02:33
  meteors. But also you get this effect of
• 1:02:36
  the Earth's motion being a bit like you're
• 1:02:37
  driving into a snowstorm. You know, if you're
• 1:02:40
  driving into a snowstorm where there's no
• 1:02:42
  wind and the snowflakes are falling down
• 1:02:43
  vertically, vertically, you will perceive
• 1:02:45
  them as coming from in front of your car, not
• 1:02:47
  overhead. And so there's a preference for
• 1:02:49
  meteor showers to be slightly more likely to
• 1:02:51
  have activity that peaks in the morning hours
• 1:02:53
  in the evening. But that's not a guarantee.
• 1:02:55
  There are some meteor showers that are at the
• 1:02:58
  highest where the radiant culminates in the
• 1:02:59
  evening sky. It just depends. Some
• 1:03:03
  like the Utrecht, are only visible for a
• 1:03:05
  couple of hours before dawn. Um, there's even
• 1:03:06
  a few meteor showers that are daylight
• 1:03:08
  showers where the radiance only really above
• 1:03:10
  the horizon during the hours of daylight. And
• 1:03:12
  we know about them primarily from radio
• 1:03:14
  observations. Radar, well not radar. People
• 1:03:17
  listening to radio reflecting off the ionized
• 1:03:20
  streaks that the meteors leave in the
• 1:03:22
  ionosphere. That allows you to see over the
• 1:03:24
  horizon to radio sessions that are
• 1:03:27
  broadcasting that you don't normally get. So
• 1:03:28
  you can hear meteor showers? Yeah, so we know
• 1:03:31
  there are daytime showers that uh, we cannot
• 1:03:33
  see at night. And some of them are possibly
• 1:03:35
  as active as the Geminids of the Perseids.
• 1:03:37
  If, you know, if we could turn the sun off, I
• 1:03:40
  mean that would be a bad thing. Please don't
• 1:03:41
  do it. If you're a super villain listening,
• 1:03:43
  do not take this as an idea, but if we
• 1:03:46
  could turn the sun off and see there are a
• 1:03:47
  couple of meteor showers in the daytime that
• 1:03:49
  could be pretty spectacular.
• 1:03:52
  Andrew Dunkley: It is all very fascinating and I suppose the
• 1:03:54
  best advice would be to go and look for the,
• 1:03:58
  the better sources of forecasting rather than
• 1:04:01
  trying to figure it out for yourself.
• 1:04:02
  And uh, and, and you've mentioned a couple of
• 1:04:04
  already comet, uh, maps and, and uh,
• 1:04:07
  what was the other one about meteors?
• 1:04:09
  Jonti Horner: For meteors, I really strongly recommend the
• 1:04:11
  International Meteor Organization. If you go
• 1:04:13
  to their website, hover over the resources
• 1:04:16
  link, click on it to get the drop down. Click
• 1:04:18
  on meteor shower calendar. They have on the
• 1:04:20
  right hand side the best showers of the year
• 1:04:23
  with information and what the moon will be
• 1:04:25
  like. But there's also on the left side a PDF
• 1:04:27
  that you can download that goes into much
• 1:04:29
  more minute detail and talks about even the
• 1:04:31
  more minor showers. Um, and that's a very
• 1:04:33
  good point of truth for meteor showers. Well,
• 1:04:36
  I kind of describe them being like three
• 1:04:38
  tiers of meteor showers, ignoring the
• 1:04:40
  outbursts. There are the big three, which are
• 1:04:42
  the Quadrantids, the Persons and the
• 1:04:44
  Geminids, which are uh, even if you're not
• 1:04:47
  that interested at all in space, and if you
• 1:04:49
  are, thanks for listening to the podcast
• 1:04:51
  anyway, but it's not really our target
• 1:04:53
  audience. But even people who are not that
• 1:04:55
  interested, that's a spectacle you can go out
• 1:04:57
  and see with them and share with them them.
• 1:04:59
  Just make sure that you figure out when the
• 1:05:00
  radiant rises from your location because you
• 1:05:02
  don't want to turn people off by looking at a
• 1:05:05
  time when you can't see meteors. So for the
• 1:05:07
  Geminids the best time is around 2am but
• 1:05:10
  depending on where you are in the world, from
• 1:05:12
  our latitude you're looking at, you can't see
• 1:05:15
  any before 9:30, 10:00 clock at night.
• 1:05:17
  Obviously if you're somewhere with daylight
• 1:05:18
  savings in the southern hemisphere, add an
• 1:05:20
  hour to that. So for you down in New South
• 1:05:23
  Wales, where the clocks change, you're
• 1:05:24
  talking after 11pm for you. But if you're in
• 1:05:26
  Northern Europe, the Geminid radiant never
• 1:05:29
  sets. So where I grew up in the uk, as soon
• 1:05:31
  as it got dark I could see them. The rate
• 1:05:33
  still got better through the night. Similarly
• 1:05:35
  for the Perseids in particular. Perseids are
• 1:05:37
  a northern hemisphere only thing. It's light
• 1:05:40
  until quite late, certainly for the high
• 1:05:41
  northern latitudes like the uk, but as soon
• 1:05:43
  as it gets dark you can see them. So they're
• 1:05:45
  the showers that uh, are well worth going out
• 1:05:48
  to look at as a beginner and you just sit out
• 1:05:50
  there. I would figure out where the radiant
• 1:05:52
  is and look 30 or 40 degrees to the left or
• 1:05:55
  right of it to get the best balance between a
• 1:05:57
  lot of meteors but decent ones to see and
• 1:06:00
  just get a comfy chair, lie back, wrap up
• 1:06:03
  warm m with the people you love and tell
• 1:06:05
  stories and relax and occasionally you'll see
• 1:06:07
  something good and it's quite addictive. You
• 1:06:08
  think, you know, I'll go to bed, but I just
• 1:06:10
  want to see one more and then, well, that's
• 1:06:12
  rubbish. So uh, I want to see another one
• 1:06:14
  that's actually good. You've then got like
• 1:06:16
  the mid tier showers which can be decent but
• 1:06:19
  you need to be a bit more dedicated for these
• 1:06:21
  are the ones where you might see 10 or 15 an
• 1:06:23
  hour instead of 50 an hour. And I, um,
• 1:06:26
  wouldn't recommend people who were beginners
• 1:06:27
  go out and see them because it's, there's not
• 1:06:29
  enough happening. And that's why I worry
• 1:06:32
  about coverage for the April Lyrids, even in
• 1:06:34
  the Northern Hemisphere, because they're just
• 1:06:36
  not that good. If you're someone who's really
• 1:06:39
  keen, you'll enjoy them. But for most people
• 1:06:41
  there'll be a letdown and you don't want to
• 1:06:43
  turn people off the subject. Then there are
• 1:06:45
  the minor showers that you frankly need to be
• 1:06:48
  very obsessive to follow. And I've seen
• 1:06:49
  stories of a lot of the science of this has
• 1:06:52
  been done by amateur astronomers and, um,
• 1:06:54
  quite often by people who are quite obsessive
• 1:06:56
  about the topic. And I
• 1:06:59
  saw one guy who was in North America where it
• 1:07:02
  gets brutal, brutal cold in the winter,
• 1:07:05
  who built himself a, an insulated coffin with
• 1:07:08
  an incredibly transparent glass lid that he
• 1:07:10
  would carry out with him that was big enough
• 1:07:12
  for him to have a notebook and write down the
• 1:07:14
  details of every meteor he saw. He could lie
• 1:07:17
  out in minus 40 degrees and I think
• 1:07:19
  that's, um, units ambivalent. I think
• 1:07:21
  Fahrenheit and Centigrade are very similar at
• 1:07:23
  that point. But he's in an insulated box that
• 1:07:26
  keeps him warm and he'd lie out all night
• 1:07:28
  recording 2 meters, 3 meters an hour. That
• 1:07:31
  isn't for me, but it is for some people. But
• 1:07:34
  when you see a meteor shower with a ZHR of
• 1:07:36
  less than about 20, I'd probably leave that
• 1:07:38
  unless you're really keen. If it's got a zhr
• 1:07:41
  of 50 plus, well worth looking out for. But
• 1:07:44
  look for when the time of maximum is for most
• 1:07:46
  meteor showers, they've got what we call a
• 1:07:49
  full width half maximum of about 24 hours.
• 1:07:51
  What that means is that, uh, the rate only
• 1:07:54
  stays above half of the peak rate for about
• 1:07:56
  24 hours for 48 hours, then it'd stay above
• 1:07:59
  a quarter of the rate and so on. For the
• 1:08:01
  Quadrantids, it's full width at quarter
• 1:08:03
  maximum of about 12 hours. So that means
• 1:08:06
  if you're six hours away from the peak, the
• 1:08:08
  rate is already down to a quarter of that
• 1:08:10
  peak. It's a very sharp peak and if you're
• 1:08:12
  looking at the wrong time, the show won't be
• 1:08:14
  as good as you'd like it to be and you'll be
• 1:08:16
  disappointed.
• 1:08:18
  Andrew Dunkley: So much to consider, Jonti, but fascinating.
• 1:08:20
  Uh, copper and meteors.
• 1:08:22
  Um, there's so much to talk about and we
• 1:08:24
  probably didn't really cover absolutely
• 1:08:27
  everything. Although we did, uh, we did hit
• 1:08:29
  on quite a fair bit of info. And of course,
• 1:08:31
  we do welcome questions and comments. So, uh,
• 1:08:34
  please, um, go to our website and,
• 1:08:36
  um, click that little AMA button at
• 1:08:39
  the top and you can send us, uh, questions
• 1:08:41
  and comments, uh, in text and audio form.
• 1:08:44
  Don't forget to tell us who you are and where
• 1:08:46
  you're from, but we're going to wrap it up
• 1:08:47
  there. Jonti, thank you so much. We'll catch
• 1:08:49
  you on the next show.
• 1:08:50
  Jonti Horner: Thank you very much.
• 1:08:52
  Andrew Dunkley: Professor Jonti Horner, professor of
• 1:08:54
  Astrophysics at the University of Southern
• 1:08:57
  Queensland, our, uh, special, uh, guest
• 1:08:59
  commentator. While Fred's, uh, on the other
• 1:09:02
  side of the planet looking at meteors. And,
• 1:09:04
  uh, just a special word for, uh, for Huw in
• 1:09:07
  the studio. He's been a little unwell lately.
• 1:09:10
  Huw, get well soon, mate. We're all thinking
• 1:09:12
  of you. And from me, Andrew Dunkley. Thanks
• 1:09:15
  for your company. We'll catch you on the next
• 1:09:16
  episode of Space Nuts.
• 1:09:19
  Jonti Horner: You'll be listening to the Space Nuts
• 1:09:21
  podcast, available at
• 1:09:24
  Apple Podcasts, Spotify,
• 1:09:27
  iHeartRadio or your favorite podcast
• 1:09:29
  player. You can also stream on
• 1:09:31
  demand@bytes.com.
• 1:09:33
  Andrew Dunkley: this has been another quality podcast
• 1:09:35
  production from bytes.com.