# Comets, Meteors & Celestial Wonders : A Cosmic Special

An episode of [Space Nuts: Astronomy Insights & Cosmic Discoveries](https://invisiblenetwork.ai/podcast/1080090608), 15 May 2026, 1 h 11 min.

Audio: https://dts.podtrac.com/redirect.mp3/pscrb.fm/rss/p/op3.dev/e/api.spreaker.com/download/episode/72016612/comets_meteors_celestial_wonders_a_cosmic_special_nordvpn_sponsor.mp3

Sponsor Link: Secure your online life...make sure your data stays yours alone. Do what we did and get NordVPN with our special deal which includes an extra 4 months for free and big savings, all at no risk to you. To check out the details visit www.nordvpn.com/spacenuts Comets, Meteors, and Celestial Wonders In this engaging episode of Space Nuts, hosts Andrew Dunkley and Professor Jonti Horner dive deep into the fascinating world of comets and meteors. With Professor Fred Watson away, Jonti brings his expertise to explore these celestial phenomena, their historical significance, and the science behind them. Episode Highlights: - Understanding Comets and Meteors: Andrew and Jonti kick off the episode by discussing the importance of comets and meteors in both ancient cultures and modern astronomy. They delve into how these celestial objects have been perceived throughout history and their impact on human events. - Recent Discoveries and Predictions: The hosts share insights on recent comet discoveries, including the intriguing Comet Chichin Chan, and discuss what we can expect from this comet in the near future. They also touch on the challenges of predicting comet brightness and visibility. - Meteor Showers Explained: Jonti explains how meteor showers occur, the significance of radiant points, and what conditions are best for viewing these spectacular events. They discuss the most notable meteor showers and when listeners can catch them in action. - The Impact of Media on Public Perception: The conversation takes a turn as Andrew and Jonti address the role of media in shaping public understanding of astronomical events, particularly the sensationalism surrounding potential alien encounters and the importance of relying on scientific facts. For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. Follow us on social media at SpaceNutsPod on Facebook, Instagram, and more. We love engaging with our community, so be sure to drop us a message or comment on your favourite platform. If you’d like to help support Space Nuts and join our growing family of insiders for commercial-free episodes and more, visit spacenutspodcast.com/about. Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing. Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support.

## Transcript

[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.

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