July 23, 2026
Far Side | Today's Space News
Astronomy Daily S05E148 — "Far Side" Thursday 23 July 2026 Starship gets a second shot at Flight 13 — with a schedule caveat worth knowing about. The first far-side lunar samples reveal that Earth has been quietly shielding the side of the Moon that faces us. Astronomers debate whether the lunar far side should be closed to industry. The Milky Way's only helium nova finally steps out from behind twenty-five years of dust. And the case that our entire galaxy once turned over. Plus a skywatch closer with a straightforward piece of advice about the Delta Aquariids: do not wait for the peak.
In this episode Starship Flight 13 ● Window opens 6:45pm EDT / 2245 GMT Thursday 23 July — 8:45am AEST and 10:45am NZST Friday 24 July. ● Schedule is not locked: Starbase road and beach closure notices point to further Pad 2 testing. ● The 16 July attempt aborted at T-0 when four of 33 Raptors missed start parameters; the limit is three. ● Two Raptors were removed and replaced before this attempt. ● First-ever Starship deployment of V3 Starlink satellites — 20 of them. ● Super Heavy splashes down in the Gulf at ~7 minutes; Ship targets the Indian Ocean off Western Australia at ~65 minutes. No catch attempts. Chang'e-6 and the solar wind ● Published in Nature Geoscience by a team at the Chinese Academy of Sciences' Institute of Geology and Geophysics. ● Based on 1,935 grams of regolith returned from the South Pole–Aitken basin on the lunar far side. ● First direct laboratory comparison of solar wind implantation between the near and far sides. ● Far-side soil records faster, deeper-penetrating particles; the neon isotope ratio sits below every near-side sample measured. ● About a quarter of the solar wind exposure at the Chang'e-5 near-side site involved wind decelerated by Earth's magnetosphere. The far-side site shows none. ● Opens the possibility of using lunar noble gases as a fossil record of Earth's magnetic field over deep time. The far side debate — NAM 2026 ● Held Tuesday 21 July at the RAS National Astronomy Meeting, University of Birmingham. Convened by Prof Martin Ward. ● For the motion: Prof Joe Silk (Johns Hopkins) and Dr Jonathan McDowell (Durham Space Research Centre). ● Against: Dr Nikita Chiu (Durham) and Dr Manuel Salvoldi (aerospace engineer and educator). ● For: the far side is the only radio-quiet site near Earth — critical for detecting the cosmic dark ages, and an exceptional platform for gravitational wave detection. ● Against: commercial investment is what makes lunar exploration sustainable, and governance can let science and industry coexist. ● Audience support for the motion rose from 68% to 76% across the debate. V445 Puppis ● Presented at NAM 2026 by John Mills, University of Warwick. ● The only confirmed helium nova in the Milky Way. Erupted in late 2000, then vanished behind its own dust for over twenty years. ● Now confirmed as a white dwarf accreting from a rare stripped helium star — only a few thousand such stars are thought to exist in the entire galaxy. ● Orbital period of 3.7 days, roughly double previous estimates. Mass transfer has resumed. ● Unexplained high-speed "bullets" of possibly oxygen-rich gas travelling up to 20 million mph (~9,000 km/s) — never seen in any other nova. ● Data from ESO's Very Large Telescope, Hubble, the Southern African Large Telescope and TESS. ● Helium novae may be one pathway to Type Ia supernovae, the standard candles used to measure cosmic expansion. The Milky Way disc flip ● Presented at NAM 2026 by Kirill Batrakov, Durham University. ● Based on 25 Milky Way-like galaxies in the Auriga simulation suite, followed across roughly 11 billion years. ● Galaxies with the most slowly rotating stellar haloes shared a major head-on merger and a disc reorientation greater than 90 degrees. ● Our stellar halo rotates at only 10–20 km/s; the disc moves at around 220 km/s. ● The Gaia-Sausage-Enceladus collision roughly 10 billion years ago is the candidate trigger. ● Batrakov describes a disc flip as likely rather than confirmed, and is looking for independent signatures. ● Separate 2026 work led by Ling Zhu, using 600,000+ giant stars from Gaia and LAMOST, found the outer dark matter halo oriented almost vertically to the stellar disc — consistent with the disc having tilted. Skywatch ● Southern Delta Aquariids are active now, running into late August, with maximum around 30 July. ● Full Moon on 29 July means peak night is close to 98% illuminated — the worst conditions of the run. ● Best window: the pre-dawn mornings from now until roughly 27 July, after moonset. ● Radiant near Skat in Aquarius. Use Fomalhaut and the Great Square of Pegasus to locate it. ● Australia and New Zealand: radiant climbs near overhead. Best from around 2am to first light. ● North America: radiant sits low in the south — fewer meteors, but a better chance of long-trailed earthgrazers. Same 2am-to-dawn window, local time. ● Sunspot region AR4493 has grown rapidly to beta-gamma-delta complexity — the highest classification — and has already fired three M-class flares in a day. Worth watching aurora alerts. Sources ● SpaceX / Space.com — Starship Flight 13 mission details and timing ● Nature Geoscience — noble gas analysis of Chang'e-6 regolith (Chinese Academy of Sciences, Institute of Geology and Geophysics) ● Royal Astronomical Society — NAM 2026 far side governance debate ● Royal Astronomical Society — NAM 2026, V445 Puppis (John Mills, University of Warwick) ● Royal Astronomical Society — NAM 2026, Milky Way disc flip (Kirill Batrakov, Durham University) ● EarthSky and the American Meteor Society — Delta Aquariid observing guidance ● NOAA Space Weather Prediction Center / EarthSky Sun News — AR4493 activity
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In this episode Starship Flight 13 ● Window opens 6:45pm EDT / 2245 GMT Thursday 23 July — 8:45am AEST and 10:45am NZST Friday 24 July. ● Schedule is not locked: Starbase road and beach closure notices point to further Pad 2 testing. ● The 16 July attempt aborted at T-0 when four of 33 Raptors missed start parameters; the limit is three. ● Two Raptors were removed and replaced before this attempt. ● First-ever Starship deployment of V3 Starlink satellites — 20 of them. ● Super Heavy splashes down in the Gulf at ~7 minutes; Ship targets the Indian Ocean off Western Australia at ~65 minutes. No catch attempts. Chang'e-6 and the solar wind ● Published in Nature Geoscience by a team at the Chinese Academy of Sciences' Institute of Geology and Geophysics. ● Based on 1,935 grams of regolith returned from the South Pole–Aitken basin on the lunar far side. ● First direct laboratory comparison of solar wind implantation between the near and far sides. ● Far-side soil records faster, deeper-penetrating particles; the neon isotope ratio sits below every near-side sample measured. ● About a quarter of the solar wind exposure at the Chang'e-5 near-side site involved wind decelerated by Earth's magnetosphere. The far-side site shows none. ● Opens the possibility of using lunar noble gases as a fossil record of Earth's magnetic field over deep time. The far side debate — NAM 2026 ● Held Tuesday 21 July at the RAS National Astronomy Meeting, University of Birmingham. Convened by Prof Martin Ward. ● For the motion: Prof Joe Silk (Johns Hopkins) and Dr Jonathan McDowell (Durham Space Research Centre). ● Against: Dr Nikita Chiu (Durham) and Dr Manuel Salvoldi (aerospace engineer and educator). ● For: the far side is the only radio-quiet site near Earth — critical for detecting the cosmic dark ages, and an exceptional platform for gravitational wave detection. ● Against: commercial investment is what makes lunar exploration sustainable, and governance can let science and industry coexist. ● Audience support for the motion rose from 68% to 76% across the debate. V445 Puppis ● Presented at NAM 2026 by John Mills, University of Warwick. ● The only confirmed helium nova in the Milky Way. Erupted in late 2000, then vanished behind its own dust for over twenty years. ● Now confirmed as a white dwarf accreting from a rare stripped helium star — only a few thousand such stars are thought to exist in the entire galaxy. ● Orbital period of 3.7 days, roughly double previous estimates. Mass transfer has resumed. ● Unexplained high-speed "bullets" of possibly oxygen-rich gas travelling up to 20 million mph (~9,000 km/s) — never seen in any other nova. ● Data from ESO's Very Large Telescope, Hubble, the Southern African Large Telescope and TESS. ● Helium novae may be one pathway to Type Ia supernovae, the standard candles used to measure cosmic expansion. The Milky Way disc flip ● Presented at NAM 2026 by Kirill Batrakov, Durham University. ● Based on 25 Milky Way-like galaxies in the Auriga simulation suite, followed across roughly 11 billion years. ● Galaxies with the most slowly rotating stellar haloes shared a major head-on merger and a disc reorientation greater than 90 degrees. ● Our stellar halo rotates at only 10–20 km/s; the disc moves at around 220 km/s. ● The Gaia-Sausage-Enceladus collision roughly 10 billion years ago is the candidate trigger. ● Batrakov describes a disc flip as likely rather than confirmed, and is looking for independent signatures. ● Separate 2026 work led by Ling Zhu, using 600,000+ giant stars from Gaia and LAMOST, found the outer dark matter halo oriented almost vertically to the stellar disc — consistent with the disc having tilted. Skywatch ● Southern Delta Aquariids are active now, running into late August, with maximum around 30 July. ● Full Moon on 29 July means peak night is close to 98% illuminated — the worst conditions of the run. ● Best window: the pre-dawn mornings from now until roughly 27 July, after moonset. ● Radiant near Skat in Aquarius. Use Fomalhaut and the Great Square of Pegasus to locate it. ● Australia and New Zealand: radiant climbs near overhead. Best from around 2am to first light. ● North America: radiant sits low in the south — fewer meteors, but a better chance of long-trailed earthgrazers. Same 2am-to-dawn window, local time. ● Sunspot region AR4493 has grown rapidly to beta-gamma-delta complexity — the highest classification — and has already fired three M-class flares in a day. Worth watching aurora alerts. Sources ● SpaceX / Space.com — Starship Flight 13 mission details and timing ● Nature Geoscience — noble gas analysis of Chang'e-6 regolith (Chinese Academy of Sciences, Institute of Geology and Geophysics) ● Royal Astronomical Society — NAM 2026 far side governance debate ● Royal Astronomical Society — NAM 2026, V445 Puppis (John Mills, University of Warwick) ● Royal Astronomical Society — NAM 2026, Milky Way disc flip (Kirill Batrakov, Durham University) ● EarthSky and the American Meteor Society — Delta Aquariid observing guidance ● NOAA Space Weather Prediction Center / EarthSky Sun News — AR4493 activity
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This episode includes AI-generated content.
WEBVTT
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Anna: The side of the Moon we never see has been
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quietly keeping a secret about our own
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planet. And this week, two very different
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groups of scientists arrived at the same
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place from opposite directions.
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Avery: One group read it out of the dirt. The other
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argued about who gets to own it.
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Anna: Meanwhile, a rocket sits on a pad in South
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Texas waiting for a second chance.
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Avery: And a star that vanished behind its own
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wreckage 25 years ago has finally
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stepped back into the light.
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Anna: Welcome to Astronomy Daily. I'm Ana.
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Avery: And I'm, um. Avery. It's Thursday 23rd
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July 2026, and this is episode
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148.
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Anna: Coming up, Starship gets another go with
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a caveat. What the far side of the Moon knows
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about Earth's magnetic field, whether that
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far side should be off limits to industry. A
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one of a kind stellar explosion finally
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identified. And the possibility that our
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entire galaxy once turned over.
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Avery: Uh, plus a skywatch closer with some
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genuinely useful advice about the Delta
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Aquarids, which is to not wait for the peak.
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Anna: Let's get into it.
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Avery: We start at Starbase, because today is meant
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to be the day.
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Anna: SpaceX is targeting Flight 13 of
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Starship with a 90 minute launch window that
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opens at 6:45 in the evening Eastern
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Time. That's 5:45 Central and
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3:45 in the afternoon on the Pacific coast.
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For those of us on this side of the world,
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that lands at a quarter to nine on Friday
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morning Australian Eastern Time and a quarter
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to 11 Friday morning in New Zealand.
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Avery: So North America gets it over dinner and we
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get it over breakfast for once, nobody has to
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set an alarm for three in the morning for
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once.
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Anna: Although, and this is the part I want to be
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upfront about, that schedule is not locked.
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Meaning? Meaning the public schedule says
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today, but the road and beach closure
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notifications around Starbase suggest
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additional testing is happening happening on
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Pad 2. Those closure notices are one of the
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more reliable tells in this business because
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they have to be filed in advance and they
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tend to reflect what's actually planned
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rather than what's been announced. So there
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is a realistic chance this
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Avery: slides again, which would make it the third
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date for Flight 13.
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Anna: It would. Let's recap how we got here because
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the arc matters. Flight 13 was first set
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for Thursday 16th July. The countdown went
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all the way to zero and then stopped. The
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flight software triggered an automatic abort
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right at T0 because four of the 33
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Raptor engines on the Super Heavy booster
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failed to reach acceptable starting
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parameters.
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Avery: And um, the threshold is 3, so
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Anna: it missed by exactly one engine. That's the
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system working as designed and it protected
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both the vehicle and the pad. Elon Musk said
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afterwards that two Raptors would be pulled
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and replaced before the next attempt.
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Avery: That's a remarkably narrow margin between a
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scrub and a launch.
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Anna: It is, and it's deliberate. The vehicle was
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cleared to fly in the first place because the
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SAA closed out its mishap investigation into
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Flight 12 on 13 July. And the
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booster had already completed a full duration
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static fire of all 33 engines back on the
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10th.
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Avery: So the hardware had been through its paces.
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It just didn't like the moment.
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Anna: That's about the size of it. Here's what
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makes this flight worth paying attention to.
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Beyond the launch itself, Blight 13 is
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carrying 20 V3 Starlink satellites,
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the next generation of the Constellation, and
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the first time Starship has ever deployed
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them.
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Avery: That's the whole point of the vehicle
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eventually. Not the spectacle, the payload.
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Anna: Right up to now, these have been test flights
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carrying simulators and mass models. This is
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the first time the thing does the job it was
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built for. Even on a suborbital trajectory
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and the flight profile. Oster and ship
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separate as usual. Super Heavy steers
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itself to a controlled splashdown in the Gulf
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about seven minutes after liftoff. No
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catch attempt with the chopstick arms on this
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one. The ship continues on,
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deploys the satellites and then comes down
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for its own splashdown in the Indian Ocean
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off the coast of Western Australia at around
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65
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Avery: minutes, which is worth flagging for our, uh,
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listeners in Perth and along that coast. You
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are not going to see it from the beach. It's
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a long way offshore, but it is your patch of
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ocean.
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Anna: It is. And for anyone in North America
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hoping to catch the launch itself, it's a
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star based departure. So the viewing sites
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around Boca Chica and South Padre island are
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the ones that matter.
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Avery: So assuming it goes.
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Anna: Assuming it goes. If you're listening to this
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on Thursday, check before you commit your
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evening. If you're listening later, you
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already know how it turned out and we'll pick
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up the result in the next episode. Either
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way, this ark has taught us not to get ahead
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of ourselves.
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Avery: Now, to the moon and to something I find
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genuinely lovely about this next result,
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which is that it turns lunar soil into a
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record of Earth.
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Anna: Go on.
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Avery: The sun blows a continuous stream of charged
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particles out across a solar system. The
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solar wind. The moon has no atmosphere and
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no global magnetic field to speak of. So
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those particles hit the surface directly and
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bury themselves in the soil over billions of
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years. The regolith becomes an archive of
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everything that struck it.
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Anna: And noble gases are the good bookkeepers.
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Avery: Exactly. Helium, neon, argon,
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krypton, xenon. They don't react with
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anything. So whatever went in stays in.
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And how deep it went tells you how fast it
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was traveling when it arrived.
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Anna: So what did they find?
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Avery: A team at the Chinese Academy of Sciences,
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Institute of Geology and Physics analyzed
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samples from Chang' E6. The mission that
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returned material from the far side from the
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south pole aitken Basin. That's
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1,935 grams of soil,
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just under 2 kilograms.
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Anna: And that's the first far side material anyone
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has ever had in a laboratory.
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Avery: Every previous return sample, Apollo, Luna,
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Chang' e5 came from the near side. So this
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is the first time anyone could directly
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compare the two hemispheres. They worked
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through seven portions using stepwise heating
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and laser extraction, measuring the isotopes
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of all five noble gases. And the far side
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soil is measurably different. The solar
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wind went in faster and went in deeper.
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Anna: Deeper, meaning higher energy.
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Avery: Higher energy, yes. The clearest signal was
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in neon. The ratio of Neon 20 to
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Neon 22 in the Cheng' E6 material
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sits below anything recorded in any near
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sight sample, which points to stronger
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processing on the way in. And the heavier
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gases krypton and xenon come out of the
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sample at different temperatures than they do
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from Chang' E5 material, which is another way
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of reading implantation depth.
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Anna: So why would the far side get hit harder?
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Avery: Because we're in the way. M
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Earth magnetosphere. As the moon
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travels around its orbit, it spends part of
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each month downstream of Earth, inside the
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long magnetic tail our planet trails behind
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it. And in that region, the solar wind
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gets slowed down before it reaches the lunar
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surface. But it's the near side that's facing
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us. So the near side is the one that catches
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at the celerated wind. The far side is
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permanently turned away and takes the full
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unmoderated stream.
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Anna: Earth has been sheltering the side of the
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moon that looks at us for 4 billion
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years.
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Avery: For 4 billion years. And the team put
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a number on it. Roughly a quarter of the
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total solar wind exposure at the Chang' e 5
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landing site involved that slowed down flow.
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At the Chang' e 6 site on the far side,
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there's no sign of it at all.
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Anna: That's a beautiful result. And I assume it
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cuts the other way as well.
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Avery: That's the part that excites me most. If the
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near site soil records how much shielding
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Earth was providing, then heavy noble gases
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in lunar Regolith become a fossil record of
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our own magnetosphere. Combine that with the
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rock magnetism record on Earth, and you have
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a completely new way of reconstructing how
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our magnetic field has changed over deep
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time.
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Anna: Which is not a small thing, given the
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magnetosphere is the reason we still have an
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atmosphere.
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Avery: Not a small thing at all. The Moon has been
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keeping notes on us, and it turns out the far
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side has the cleaner copy. Which, as
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it happens, is exactly why a room full of
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astronomers spent Tuesday evening arguing
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about what we're allowed to do out there.
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Anna: So this was at the Royal Astronomical
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Society's National Astronomy Meeting, which
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is running this week at the University of
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Birmingham. On Tuesday evening, they staged a
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formal debate on a single proposition, that
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the far side of the Moon should be preserved
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solely for scientific endeavors.
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Avery: And the answer is presumably not obvious or
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there'd be no debate.
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Anna: It's genuinely not. Arguing in favor were
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Joe Silk of Johns Hopkins and Jonathan
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McDowell, who most of our listeners will know
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from Jonathan's space report and who is now
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an honorary professor at Durham Space
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Research Center. After decades at the Harvard
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Smithsonian center for Astrophysica, um, and
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against M. Nikita Chu, also at Durham, who
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works on space technology governance, and
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manuel Salvoldi, an Aram space engineer with
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25 years across industry and academia.
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Barton Ward convened it. The case for
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protection rests on one physical fact. The
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far side is the only radio quiet real
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estate anywhere near Earth.
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Avery: The Moon is tidally locked, so the same
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hemisphere always faces us, which means the
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far side is permanently shielded from every
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transmitter, every radar, every broadcast on
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this planet. And that matters because.
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Anna: Because there are signals we want to detect
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that are drowned out everywhere else. The
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cosmic dark ages, the stretch of time after
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the Big Bang before the first star switched
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on. The radio emission from that era is faint
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and it's low frequency. And Earth is far too
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noisy a place to hear it. A far side radio
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telescope is arguably the only way we ever
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will.
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Avery: That's a fairly specific and, um,
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irreplaceable thing to be arguing about.
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Anna: It is, and Cilk's framing was essentially
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generational, that we should protect these
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conditions for science. That won't be done
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for decades, because the questions at stake
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are whether we're alone and how the universe
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began.
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Avery: And, um, the physical case doesn't stop at
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radio.
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Anna: No. They also argued the far side would be an
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exceptional site for gravitational wave
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detection. No atmosphere, no weather, very
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little seismic activity compared with Earth,
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and no artificial light, which is becoming a
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real problem for optical astronomy down here.
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Avery: So what's the counterargument, because leave
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it alone is easy to say.
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Anna: The counterargument is about sustainability,
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and I thought it was stronger than people
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might expect. Few's position was that this
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isn't a challenge to the value of the
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science, it's a question of how you keep
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going back at all. Lunar exploration that
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depends entirely on government funding is
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fragile. Commercial investment is what makes
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it resilient. And her argument was that you
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can have both under proper governance, that
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an inclusive CIS lunar economy on the far
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side doesn't have to turn into a free for
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all.
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Avery: Which is a fair point. A protected region
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nobody can afford to reach is protected in a
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fairly useless way.
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Anna: That's the tension. Exactly. And McDowell's
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put the stakes in the broadest possible
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terms. His line was is the whole solar system
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up for grabs or do we set aside reserves?
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Avery: That's the real question, isn't it? Not the
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Moon specifically.
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Anna: Not the Moon specifically. His argument was
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that whatever we decide in the next few years
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becomes the precedent for everything after
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Mars, the asteroids, all of it.
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Avery: Did they take a vote?
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Anna: They did. Before and after. By QR code.
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Support for the motion went from 68%
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to 76%, though the room moved
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towards protection, which, given the
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audience, isn't a shock. But an eight point
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swing after hearing both sides is a real
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result rather than a formality. And it fed
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into a full session the next day on lunar
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governance and regulation.
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Avery: And in the meantime, Chang' E6 has just
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demonstrated that the far side is
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scientifically valuable in ways nobody had
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directly measured measured until this month,
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which rather
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Anna: sharpens the argument staying at the National
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Avery: Astronomy Meeting because there is a
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genuinely extraordinary object I want to talk
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about, and it lives in our skies.
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Southern skies Puppis, which for our
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Australian and New Zealand listeners is well
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placed for a good chunk of the year, and for
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northern listeners sits low on the south. The
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object is V445 Puppis,
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and it is the only confirmed helium nova in
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the Milky Way.
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Anna: Define helium nova.
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Avery: So a nova, an ordinary nova,
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is a white dwarf in a binary system stealing
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gas off its companion. That gas piles
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up on the surface, pressure and temperature
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climb, and eventually you get a runaway
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thermonuclear explosion. It doesn't
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destroy the star, it just blows the
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accumulated layer off. And in virtually
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every case, that stolen material is
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hydrogen rich, because hydrogen is what stars
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are mostly made of.
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Anna: And this one isn't.
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Avery: This one has essentially no hydrogen at all,
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which is a very strange thing for a stellar
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explosion to be missing, given hydrogen is
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the most abundant element in the universe. So
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the obvious question is what is it stealing
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from?
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Anna: And nobody could see.
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Avery: Nobody could see. V445
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puppys erupted in late 2000, and it
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threw out an enormous bipolar outflow. Two
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lobes of material streaming in opposite
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directions, more than a trillion miles
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across. But the eruption also created a thick
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disk of dust that completely swallowed the
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system. For more than 20 years, astronomers
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could watch the debris expanding, but they
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could not see what was inside it. The dust
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has now thinned enough. John Mills, a
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researcher and PhD student at the University
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of Warwick, put together observations
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spanning two decades to finally see through
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using what a stack of instruments.
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Infrared from the Very Large Telescope in
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Chile, Optical imaging from Hubble,
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Long term spectroscopy from the Southern
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African Large Telescope and photometry from
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tess. And the answer is a white dwarf
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feeding off a helium star.
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Anna: And a helium star is a star
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Avery: that has been stripped of its outer hydrogen
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envelope, most likely by the companion it's
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now feeding. They are genuinely rare.
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The estimate is a few thousand stripped
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helium stars among the hundreds of billions
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of stars in the entire galaxy.
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Anna: So one of the rarest kinds of stars in the
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only known example of one of the rarest kinds
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of explosions.
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Avery: And it's already loading the gun again. The
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system is actively transferring material once
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more. The two stars orbit each other every
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3.7 days, which is around twice as
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long as anyone previously thought.
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Anna: You said there was a mystery.
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Avery: The bullets. The bullets embedded in the
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outflowing debris are discrete clumps of gas,
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possibly oxygen rich, though the composition
382
00:14:49.310 --> 00:14:51.870
isn't nailed down. Moving at up to 20
383
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million miles an hour, that's roughly
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9,000 kilometers per second, around
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3% of the speed of light.
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Anna: And nothing like that has been seen
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elsewhere.
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Avery: Nothing like it in any other nova anywhere.
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Mills suspects they formed after the outburst
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rather than during it. But as he put it,
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their origin is a mystery.
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Anna: Which is the honest answer. And I appreciate
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that he said it.
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Avery: So do I. Now, the reason this matters. Beyond
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its own strangeness, Astronomers suspect that
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repeated helium rich eruptions on a white
397
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dwarf might be one of the pathways that
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eventually produces a type 1A supernova.
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Anna: And type IAs are the standard candles.
400
00:15:29.400 --> 00:15:31.800
Avery: They are. They explode with remarkably
401
00:15:31.800 --> 00:15:33.600
consistent brightness, which is what makes
402
00:15:33.600 --> 00:15:35.680
them useful as distance markers across the
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universe. They're how we measured cosmic
404
00:15:38.040 --> 00:15:40.360
expansion. The work that won the Nobel Prize
405
00:15:40.360 --> 00:15:42.320
for the discovery that the expansion is
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accelerating.
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Anna: So the ruler we use to measure the universe
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depends on understanding how these things
409
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detonate.
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Avery: It does. And whether helium novae actually
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get there is still an open question. But
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V445 Puppis is now the clearest
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laboratory anyone has for testing it. And it
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took 25 years of dust clearing to get the
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door open.
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00:16:03.120 --> 00:16:05.440
Anna: Last story before we look up. And it's the
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biggest one in terms of sheer scale. There's
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a case being made that the entire Milky Way
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once flipped over.
420
00:16:12.000 --> 00:16:14.640
Avery: Flipped over how exactly? Because a galaxy
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doesn't have a right way up.
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Anna: It doesn't. And that's the right instinct.
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What's being proposed is a change of
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orientation. That the disk of our galaxy
425
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reoriented itself by more than 90 degrees
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relative to the halo of old stars around it.
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Avery: And what put that idea on the table?
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Anna: A puzzle that's been sitting there since
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Gaia. Our galaxy has a flat disk where
430
00:16:35.500 --> 00:16:37.980
most of the stars live. And around that a
431
00:16:37.980 --> 00:16:40.860
much larger, much sparser stellar halo.
432
00:16:41.020 --> 00:16:43.420
Mostly stars that formed in smaller galaxies
433
00:16:43.420 --> 00:16:45.460
and got absorbed when those galaxies were
434
00:16:45.460 --> 00:16:47.740
Avery: pulled in debris from past meals.
435
00:16:47.980 --> 00:16:50.740
Anna: Essentially. And Gaia showed that the halo
436
00:16:50.740 --> 00:16:53.660
barely rotates. It creeps around at something
437
00:16:53.660 --> 00:16:56.540
like 10 to 20 kilometers per second. The
438
00:16:56.540 --> 00:16:58.660
disk by comparison is moving at about
439
00:16:58.660 --> 00:16:59.580
220.
440
00:17:00.140 --> 00:17:02.300
Avery: That is a very large discrepancy.
441
00:17:02.540 --> 00:17:04.820
Anna: It is. And nobody had a satisfying
442
00:17:04.820 --> 00:17:07.580
explanation. So Kirill Botrikov at
443
00:17:07.580 --> 00:17:10.060
Durham went looking for one in simulations.
444
00:17:10.060 --> 00:17:13.060
The Auriga Suite, which models Milky Way like
445
00:17:13.060 --> 00:17:15.900
galaxies in detail. He took 25 of them
446
00:17:15.980 --> 00:17:18.300
and followed their evolution across roughly
447
00:17:18.300 --> 00:17:21.130
11 billion years. And the
448
00:17:21.130 --> 00:17:23.770
galaxies that ended up with the most slowly
449
00:17:23.770 --> 00:17:26.410
rotating halos had two things in common.
450
00:17:26.410 --> 00:17:29.210
They'd experienced a major head on merger
451
00:17:29.530 --> 00:17:32.250
and their disks had reoriented by more than
452
00:17:32.250 --> 00:17:33.050
90 degrees.
453
00:17:33.450 --> 00:17:35.690
Avery: And we know we had a major head on merger.
454
00:17:35.850 --> 00:17:38.850
Anna: We do. Gaia Sausage, Enceladus. The
455
00:17:38.850 --> 00:17:41.170
collision roughly 10 billion years ago that
456
00:17:41.170 --> 00:17:43.610
dumped an enormous quantity of stars into our
457
00:17:43.610 --> 00:17:46.130
halo and is the reason the halo looks the way
458
00:17:46.130 --> 00:17:46.570
it does.
459
00:17:47.060 --> 00:17:49.140
Avery: So the proposal is that the same collision
460
00:17:49.140 --> 00:17:51.820
exerted a gravitational torque on our disk
461
00:17:51.820 --> 00:17:54.060
and slowly turned it over inside the
462
00:17:54.060 --> 00:17:55.700
surrounding dark matter halo.
463
00:17:56.020 --> 00:17:58.820
Anna: Slowly meaning over hundreds of
464
00:17:58.820 --> 00:18:00.980
millions of years. Nothing about this was
465
00:18:00.980 --> 00:18:03.220
sudden, but the end state is that the plane
466
00:18:03.220 --> 00:18:05.620
the sun orbits in today may bear no
467
00:18:05.620 --> 00:18:07.860
relationship to the plane stars were orbiting
468
00:18:07.860 --> 00:18:09.220
in before the collision.
469
00:18:09.540 --> 00:18:11.620
Avery: That does something odd to my sense of place.
470
00:18:11.860 --> 00:18:14.500
Anna: It does mine too. And I want to be careful
471
00:18:14.500 --> 00:18:16.780
here because Botcherkov himself is careful.
472
00:18:16.940 --> 00:18:19.580
His position is that a disk flip is a likely
473
00:18:19.660 --> 00:18:22.540
explanation given how slowly the halo turns,
474
00:18:22.620 --> 00:18:24.780
but that it's too early to claim it with full
475
00:18:24.780 --> 00:18:27.420
confidence. What he wants is independent
476
00:18:27.420 --> 00:18:30.260
signatures, other scars that a reorientation
477
00:18:30.260 --> 00:18:31.980
on that Scale should have left behind.
478
00:18:32.380 --> 00:18:34.060
Avery: Is there anything pointing the same way
479
00:18:34.060 --> 00:18:34.380
already?
480
00:18:34.700 --> 00:18:37.060
Anna: There is, and it's suggestive rather than
481
00:18:37.060 --> 00:18:39.660
conclusive. Separate work this year led by
482
00:18:39.660 --> 00:18:42.300
Ling Xu used the motions of more than
483
00:18:42.300 --> 00:18:45.090
600,000 giant stars from Gaia and the
484
00:18:45.240 --> 00:18:47.960
LAMOST survey to reconstruct the shape of our
485
00:18:47.960 --> 00:18:50.800
dark matter halo. And the outer halo appears
486
00:18:50.800 --> 00:18:52.690
to be oriented almost vertically relative,
487
00:18:52.690 --> 00:18:53.520
uh, to the
488
00:18:53.520 --> 00:18:56.080
Avery: stellar disk, which is what you'd expect if
489
00:18:56.080 --> 00:18:58.200
the inner part tilted and the outer part
490
00:18:58.200 --> 00:18:58.680
didn't.
491
00:18:58.920 --> 00:19:01.520
Anna: That's the reading. The outer halo kept the
492
00:19:01.520 --> 00:19:04.160
old orientation. The disk and inner halo
493
00:19:04.160 --> 00:19:06.800
swung round. Two independent lines of
494
00:19:06.800 --> 00:19:09.160
evidence converging on the same story from
495
00:19:09.160 --> 00:19:12.050
completely different data. Not proof,
496
00:19:12.370 --> 00:19:14.410
but it's the kind of thing that turns a
497
00:19:14.410 --> 00:19:17.410
curiosity into a research program. And
498
00:19:17.410 --> 00:19:19.690
I rather like that. The biggest structural
499
00:19:19.690 --> 00:19:22.490
question about our own galaxy is one we can
500
00:19:22.490 --> 00:19:25.170
only answer by looking at it from the inside.
501
00:19:25.570 --> 00:19:27.050
Avery: Right, Time to look up.
502
00:19:27.050 --> 00:19:29.410
And Anna, uh, we have actual advice today
503
00:19:29.410 --> 00:19:30.610
rather than a countdown.
504
00:19:30.930 --> 00:19:33.850
Anna: We do. And the advice is don't wait for the
505
00:19:33.850 --> 00:19:34.210
peak.
506
00:19:34.530 --> 00:19:35.170
Avery: Explain.
507
00:19:35.410 --> 00:19:38.130
Anna: The southern Delta Aquarids are running now.
508
00:19:38.520 --> 00:19:41.000
The shower is already active and it stays
509
00:19:41.000 --> 00:19:43.880
active into late August. The American Meteor
510
00:19:43.880 --> 00:19:46.680
Society puts maximum activity around the
511
00:19:46.680 --> 00:19:47.560
30th of July.
512
00:19:48.040 --> 00:19:50.520
Avery: And the problem with the 30th is the moon.
513
00:19:50.680 --> 00:19:53.400
Anna: The moon is the problem. Full moon falls on
514
00:19:53.400 --> 00:19:56.320
the 29th of July. So on peak night, you're
515
00:19:56.320 --> 00:19:59.080
looking at a sky that is something like 98%
516
00:19:59.160 --> 00:20:01.680
illuminated. That will wash out most of the
517
00:20:01.680 --> 00:20:04.560
shower. Because Delta Aquariad meteors tend
518
00:20:04.560 --> 00:20:07.400
towards long, graceful trails rather than
519
00:20:07.400 --> 00:20:09.980
bright fireballs. They're exactly the kind
520
00:20:09.980 --> 00:20:11.300
that moonlight erases.
521
00:20:11.780 --> 00:20:13.780
Avery: So the peak is the worst night of the run.
522
00:20:14.180 --> 00:20:16.900
Anna: Close to it. But here's the good news. This
523
00:20:16.900 --> 00:20:19.420
shower has no sharp maximum. It
524
00:20:19.420 --> 00:20:21.980
rambles. Rates build slowly and stay
525
00:20:21.980 --> 00:20:24.740
roughly level for well over a week. Which
526
00:20:24.740 --> 00:20:27.140
means the mornings between now and about the
527
00:20:27.140 --> 00:20:29.980
27th are better than peak night because the
528
00:20:29.980 --> 00:20:32.700
waxing gibbous moon still sets before the
529
00:20:32.700 --> 00:20:33.700
radiant gets high.
530
00:20:34.350 --> 00:20:36.630
Avery: So the window is after moonset, before
531
00:20:36.630 --> 00:20:39.550
Anna: dawn, after moonset, before dawn. That's
532
00:20:39.550 --> 00:20:41.790
your window. And it applies wherever you are.
533
00:20:41.950 --> 00:20:44.550
Where do we look? The radiant sits near the
534
00:20:44.550 --> 00:20:47.390
star Skat in Aquarius. The easiest way
535
00:20:47.390 --> 00:20:50.069
in is to find Fomalhaut bright and
536
00:20:50.069 --> 00:20:52.950
noticeably alone in a fairly empty patch of
537
00:20:52.950 --> 00:20:55.790
sky. And work from there. The Great Square of
538
00:20:55.790 --> 00:20:57.230
Pegasus helps as well.
539
00:20:57.390 --> 00:20:59.070
Avery: And, um, that's a very different experience
540
00:20:59.230 --> 00:21:01.150
depending on which hemisphere you're in.
541
00:21:01.780 --> 00:21:04.260
Anna: Completely different from Australia and New
542
00:21:04.260 --> 00:21:06.820
Zealand. The radiant climbs close to overhead
543
00:21:06.820 --> 00:21:09.620
in the pre dawn hours. This is genuinely
544
00:21:09.620 --> 00:21:11.900
our Shower. The southern part of the world
545
00:21:11.900 --> 00:21:14.820
gets the best of it every year from Sydney or
546
00:21:14.820 --> 00:21:17.219
Auckland, anywhere from about 2 in the
547
00:21:17.219 --> 00:21:18.660
morning until first light.
548
00:21:18.980 --> 00:21:21.140
Avery: And for our North American listeners, who are
549
00:21:21.140 --> 00:21:22.660
the largest part of this audience,
550
00:21:22.980 --> 00:21:25.300
Anna: you still get a good showing, but the
551
00:21:25.300 --> 00:21:27.940
radiance stays lower in the southern sky, so
552
00:21:27.940 --> 00:21:29.980
you'll see fewer of them and they'll come in
553
00:21:29.980 --> 00:21:32.580
at shallower angles. And the upside of a low
554
00:21:32.580 --> 00:21:35.460
radiant is Earth grazers, meteors that
555
00:21:35.460 --> 00:21:37.900
skim along the atmosphere and leave much
556
00:21:37.900 --> 00:21:40.620
longer trails than usual. The best hours are
557
00:21:40.620 --> 00:21:43.300
the same from around 2 in the morning local
558
00:21:43.300 --> 00:21:46.110
time, uh, until dawn. So 2 to 5am, um,
559
00:21:46.110 --> 00:21:48.500
eastern and the equivalent across Central
560
00:21:48.660 --> 00:21:49.940
Mountain and Pacific.
561
00:21:50.340 --> 00:21:52.340
Avery: And get south facing and dark.
562
00:21:52.500 --> 00:21:55.260
Anna: Get south facing, get away from lights and
563
00:21:55.260 --> 00:21:57.980
give your eyes 20 minutes to adapt before you
564
00:21:57.980 --> 00:21:58.980
judge whether it's working.
565
00:21:59.640 --> 00:22:01.640
Avery: One more thing. And, um, this one is a watch
566
00:22:01.720 --> 00:22:03.880
this space rather than a forecast.
567
00:22:04.200 --> 00:22:05.720
Anna: The sun has woken up.
568
00:22:06.120 --> 00:22:07.880
Avery: Sunspot 4493.
569
00:22:08.120 --> 00:22:10.400
Anna: That one. It appeared essentially from
570
00:22:10.400 --> 00:22:12.520
nothing over the space of a couple of days
571
00:22:12.520 --> 00:22:15.480
and grew fast. And it now has what's called
572
00:22:15.480 --> 00:22:17.800
a beta gamma delta magnetic
573
00:22:17.800 --> 00:22:20.240
classification, which is the most complex
574
00:22:20.240 --> 00:22:22.800
classification there is. Regions like that
575
00:22:22.800 --> 00:22:24.680
are, uh, where the big flares come from.
576
00:22:25.110 --> 00:22:27.600
Avery: And it's already produced some 3M M
577
00:22:27.670 --> 00:22:30.150
Anna: class flares inside a single day. The
578
00:22:30.150 --> 00:22:33.150
Strongest an M M3.4, each of
579
00:22:33.150 --> 00:22:35.710
them causing brief minor radio blackouts
580
00:22:35.710 --> 00:22:37.270
across different parts of the world.
581
00:22:37.590 --> 00:22:39.670
Forecasters have been putting the odds of
582
00:22:39.670 --> 00:22:42.150
further M M class activity at better than
583
00:22:42.150 --> 00:22:44.590
even with a smaller chance of an X class
584
00:22:44.590 --> 00:22:44.950
event.
585
00:22:45.350 --> 00:22:47.310
Avery: So it's worth keeping an eye on the aurora
586
00:22:47.310 --> 00:22:48.630
alerts it is.
587
00:22:48.950 --> 00:22:51.630
Anna: Earlier this week, a fast solar wind stream
588
00:22:51.630 --> 00:22:53.910
from a coronal hole pushed conditions to
589
00:22:53.910 --> 00:22:56.620
minor storm level, with aurora possible as
590
00:22:56.850 --> 00:22:59.530
far equatorward as Hobart in the south and
591
00:22:59.530 --> 00:23:02.210
Seattle and Edinburgh in the north. That
592
00:23:02.210 --> 00:23:04.850
particular stream is easing now. But with a
593
00:23:04.850 --> 00:23:07.490
region that complex facing us, the situation
594
00:23:07.570 --> 00:23:08.690
can change quickly.
595
00:23:09.010 --> 00:23:11.010
Avery: And Southern hemisphere observers have the
596
00:23:11.010 --> 00:23:13.009
advantage of long winter nights right now,
597
00:23:13.170 --> 00:23:15.970
while northern observers are fighting short
598
00:23:15.970 --> 00:23:18.210
summer ones. Swings and
599
00:23:18.210 --> 00:23:19.250
roundabouts.
600
00:23:19.490 --> 00:23:22.370
Anna: That's episode 148, Starship waiting
601
00:23:22.370 --> 00:23:25.260
on a window that may or may not hold, a far
602
00:23:25.260 --> 00:23:27.260
side that's been quietly recording our
603
00:23:27.260 --> 00:23:29.860
magnetic field and an argument about whether
604
00:23:29.860 --> 00:23:30.820
we should leave it alone.
605
00:23:30.900 --> 00:23:33.740
Avery: Plus a star that spent 25 years behind a
606
00:23:33.740 --> 00:23:36.180
curtain and the galaxy that may have rolled
607
00:23:36.180 --> 00:23:37.220
over in its sleep.
608
00:23:37.220 --> 00:23:39.500
Anna: Show notes, sources and everything else are
609
00:23:39.500 --> 00:23:41.820
at astronomydaily, IO or
610
00:23:41.820 --> 00:23:44.340
astrodaily Pod, wherever you like to find us.
611
00:23:44.420 --> 00:23:46.500
Avery: If you're up before dawn this week chasing
612
00:23:46.500 --> 00:23:49.260
Delta Aquariids, we'd love to see what you
613
00:23:49.260 --> 00:23:49.620
catch.
614
00:23:49.620 --> 00:23:50.660
Anna: We'll be back tomorrow.
615
00:23:50.660 --> 00:23:52.200
Avery: Until then, clear skies.
0
00:00:00.000 --> 00:00:02.720
Anna: The side of the Moon we never see has been
1
00:00:02.720 --> 00:00:04.800
quietly keeping a secret about our own
2
00:00:04.800 --> 00:00:06.960
planet. And this week, two very different
3
00:00:06.960 --> 00:00:09.200
groups of scientists arrived at the same
4
00:00:09.200 --> 00:00:10.960
place from opposite directions.
5
00:00:11.280 --> 00:00:13.440
Avery: One group read it out of the dirt. The other
6
00:00:13.440 --> 00:00:15.120
argued about who gets to own it.
7
00:00:15.200 --> 00:00:17.800
Anna: Meanwhile, a rocket sits on a pad in South
8
00:00:17.800 --> 00:00:19.760
Texas waiting for a second chance.
9
00:00:20.000 --> 00:00:22.040
Avery: And a star that vanished behind its own
10
00:00:22.040 --> 00:00:24.760
wreckage 25 years ago has finally
11
00:00:24.760 --> 00:00:26.000
stepped back into the light.
12
00:00:26.520 --> 00:00:29.080
Anna: Welcome to Astronomy Daily. I'm Ana.
13
00:00:29.160 --> 00:00:31.548
Avery: And I'm, um. Avery. It's Thursday 23rd
14
00:00:31.705 --> 00:00:34.360
July 2026, and this is episode
15
00:00:34.360 --> 00:00:35.560
148.
16
00:00:35.880 --> 00:00:38.720
Anna: Coming up, Starship gets another go with
17
00:00:38.720 --> 00:00:41.440
a caveat. What the far side of the Moon knows
18
00:00:41.440 --> 00:00:43.640
about Earth's magnetic field, whether that
19
00:00:43.640 --> 00:00:46.240
far side should be off limits to industry. A
20
00:00:46.240 --> 00:00:48.880
one of a kind stellar explosion finally
21
00:00:48.880 --> 00:00:51.360
identified. And the possibility that our
22
00:00:51.360 --> 00:00:53.720
entire galaxy once turned over.
23
00:00:54.080 --> 00:00:56.090
Avery: Uh, plus a skywatch closer with some
24
00:00:56.090 --> 00:00:58.410
genuinely useful advice about the Delta
25
00:00:58.410 --> 00:01:01.250
Aquarids, which is to not wait for the peak.
26
00:01:01.410 --> 00:01:02.370
Anna: Let's get into it.
27
00:01:02.450 --> 00:01:05.210
Avery: We start at Starbase, because today is meant
28
00:01:05.210 --> 00:01:05.970
to be the day.
29
00:01:06.210 --> 00:01:08.930
Anna: SpaceX is targeting Flight 13 of
30
00:01:08.930 --> 00:01:11.370
Starship with a 90 minute launch window that
31
00:01:11.370 --> 00:01:14.290
opens at 6:45 in the evening Eastern
32
00:01:14.290 --> 00:01:16.930
Time. That's 5:45 Central and
33
00:01:16.930 --> 00:01:19.730
3:45 in the afternoon on the Pacific coast.
34
00:01:20.080 --> 00:01:22.000
For those of us on this side of the world,
35
00:01:22.000 --> 00:01:24.560
that lands at a quarter to nine on Friday
36
00:01:24.560 --> 00:01:27.320
morning Australian Eastern Time and a quarter
37
00:01:27.320 --> 00:01:29.680
to 11 Friday morning in New Zealand.
38
00:01:30.000 --> 00:01:32.360
Avery: So North America gets it over dinner and we
39
00:01:32.360 --> 00:01:35.000
get it over breakfast for once, nobody has to
40
00:01:35.000 --> 00:01:37.280
set an alarm for three in the morning for
41
00:01:37.280 --> 00:01:37.600
once.
42
00:01:37.680 --> 00:01:40.200
Anna: Although, and this is the part I want to be
43
00:01:40.200 --> 00:01:43.200
upfront about, that schedule is not locked.
44
00:01:43.360 --> 00:01:45.840
Meaning? Meaning the public schedule says
45
00:01:45.840 --> 00:01:48.080
today, but the road and beach closure
46
00:01:48.080 --> 00:01:50.480
notifications around Starbase suggest
47
00:01:50.560 --> 00:01:52.260
additional testing is happening happening on
48
00:01:52.260 --> 00:01:54.940
Pad 2. Those closure notices are one of the
49
00:01:54.940 --> 00:01:57.340
more reliable tells in this business because
50
00:01:57.340 --> 00:01:59.300
they have to be filed in advance and they
51
00:01:59.300 --> 00:02:01.420
tend to reflect what's actually planned
52
00:02:01.420 --> 00:02:03.580
rather than what's been announced. So there
53
00:02:03.580 --> 00:02:05.260
is a realistic chance this
54
00:02:05.260 --> 00:02:07.460
Avery: slides again, which would make it the third
55
00:02:07.460 --> 00:02:08.700
date for Flight 13.
56
00:02:09.180 --> 00:02:11.980
Anna: It would. Let's recap how we got here because
57
00:02:11.980 --> 00:02:14.940
the arc matters. Flight 13 was first set
58
00:02:14.940 --> 00:02:17.860
for Thursday 16th July. The countdown went
59
00:02:17.860 --> 00:02:20.310
all the way to zero and then stopped. The
60
00:02:20.310 --> 00:02:22.710
flight software triggered an automatic abort
61
00:02:22.710 --> 00:02:25.670
right at T0 because four of the 33
62
00:02:25.670 --> 00:02:27.950
Raptor engines on the Super Heavy booster
63
00:02:28.030 --> 00:02:29.870
failed to reach acceptable starting
64
00:02:29.870 --> 00:02:30.510
parameters.
65
00:02:30.670 --> 00:02:32.790
Avery: And um, the threshold is 3, so
66
00:02:32.790 --> 00:02:35.670
Anna: it missed by exactly one engine. That's the
67
00:02:35.670 --> 00:02:38.150
system working as designed and it protected
68
00:02:38.150 --> 00:02:41.150
both the vehicle and the pad. Elon Musk said
69
00:02:41.150 --> 00:02:43.350
afterwards that two Raptors would be pulled
70
00:02:43.350 --> 00:02:45.230
and replaced before the next attempt.
71
00:02:45.470 --> 00:02:47.750
Avery: That's a remarkably narrow margin between a
72
00:02:47.750 --> 00:02:48.750
scrub and a launch.
73
00:02:49.330 --> 00:02:51.850
Anna: It is, and it's deliberate. The vehicle was
74
00:02:51.850 --> 00:02:53.930
cleared to fly in the first place because the
75
00:02:53.930 --> 00:02:56.810
SAA closed out its mishap investigation into
76
00:02:56.810 --> 00:02:59.530
Flight 12 on 13 July. And the
77
00:02:59.530 --> 00:03:02.130
booster had already completed a full duration
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static fire of all 33 engines back on the
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10th.
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Avery: So the hardware had been through its paces.
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It just didn't like the moment.
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Anna: That's about the size of it. Here's what
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makes this flight worth paying attention to.
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Beyond the launch itself, Blight 13 is
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carrying 20 V3 Starlink satellites,
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the next generation of the Constellation, and
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the first time Starship has ever deployed
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them.
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Avery: That's the whole point of the vehicle
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eventually. Not the spectacle, the payload.
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Anna: Right up to now, these have been test flights
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carrying simulators and mass models. This is
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the first time the thing does the job it was
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built for. Even on a suborbital trajectory
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and the flight profile. Oster and ship
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separate as usual. Super Heavy steers
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itself to a controlled splashdown in the Gulf
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about seven minutes after liftoff. No
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catch attempt with the chopstick arms on this
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one. The ship continues on,
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deploys the satellites and then comes down
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for its own splashdown in the Indian Ocean
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off the coast of Western Australia at around
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65
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Avery: minutes, which is worth flagging for our, uh,
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listeners in Perth and along that coast. You
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are not going to see it from the beach. It's
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a long way offshore, but it is your patch of
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ocean.
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Anna: It is. And for anyone in North America
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hoping to catch the launch itself, it's a
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star based departure. So the viewing sites
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around Boca Chica and South Padre island are
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the ones that matter.
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Avery: So assuming it goes.
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Anna: Assuming it goes. If you're listening to this
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on Thursday, check before you commit your
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evening. If you're listening later, you
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already know how it turned out and we'll pick
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up the result in the next episode. Either
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way, this ark has taught us not to get ahead
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of ourselves.
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Avery: Now, to the moon and to something I find
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genuinely lovely about this next result,
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which is that it turns lunar soil into a
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record of Earth.
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Anna: Go on.
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Avery: The sun blows a continuous stream of charged
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particles out across a solar system. The
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solar wind. The moon has no atmosphere and
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no global magnetic field to speak of. So
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those particles hit the surface directly and
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bury themselves in the soil over billions of
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years. The regolith becomes an archive of
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everything that struck it.
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Anna: And noble gases are the good bookkeepers.
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Avery: Exactly. Helium, neon, argon,
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krypton, xenon. They don't react with
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anything. So whatever went in stays in.
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And how deep it went tells you how fast it
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was traveling when it arrived.
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Anna: So what did they find?
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Avery: A team at the Chinese Academy of Sciences,
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Institute of Geology and Physics analyzed
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samples from Chang' E6. The mission that
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returned material from the far side from the
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south pole aitken Basin. That's
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1,935 grams of soil,
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just under 2 kilograms.
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Anna: And that's the first far side material anyone
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has ever had in a laboratory.
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Avery: Every previous return sample, Apollo, Luna,
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Chang' e5 came from the near side. So this
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is the first time anyone could directly
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compare the two hemispheres. They worked
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through seven portions using stepwise heating
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and laser extraction, measuring the isotopes
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of all five noble gases. And the far side
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soil is measurably different. The solar
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wind went in faster and went in deeper.
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Anna: Deeper, meaning higher energy.
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Avery: Higher energy, yes. The clearest signal was
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in neon. The ratio of Neon 20 to
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Neon 22 in the Cheng' E6 material
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sits below anything recorded in any near
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sight sample, which points to stronger
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processing on the way in. And the heavier
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gases krypton and xenon come out of the
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sample at different temperatures than they do
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from Chang' E5 material, which is another way
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of reading implantation depth.
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Anna: So why would the far side get hit harder?
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Avery: Because we're in the way. M
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Earth magnetosphere. As the moon
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travels around its orbit, it spends part of
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each month downstream of Earth, inside the
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long magnetic tail our planet trails behind
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it. And in that region, the solar wind
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gets slowed down before it reaches the lunar
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surface. But it's the near side that's facing
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us. So the near side is the one that catches
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at the celerated wind. The far side is
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permanently turned away and takes the full
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unmoderated stream.
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Anna: Earth has been sheltering the side of the
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moon that looks at us for 4 billion
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years.
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Avery: For 4 billion years. And the team put
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a number on it. Roughly a quarter of the
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total solar wind exposure at the Chang' e 5
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landing site involved that slowed down flow.
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At the Chang' e 6 site on the far side,
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there's no sign of it at all.
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Anna: That's a beautiful result. And I assume it
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cuts the other way as well.
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Avery: That's the part that excites me most. If the
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near site soil records how much shielding
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Earth was providing, then heavy noble gases
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in lunar Regolith become a fossil record of
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our own magnetosphere. Combine that with the
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rock magnetism record on Earth, and you have
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a completely new way of reconstructing how
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our magnetic field has changed over deep
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time.
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Anna: Which is not a small thing, given the
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magnetosphere is the reason we still have an
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atmosphere.
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Avery: Not a small thing at all. The Moon has been
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keeping notes on us, and it turns out the far
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side has the cleaner copy. Which, as
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it happens, is exactly why a room full of
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astronomers spent Tuesday evening arguing
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about what we're allowed to do out there.
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Anna: So this was at the Royal Astronomical
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Society's National Astronomy Meeting, which
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is running this week at the University of
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Birmingham. On Tuesday evening, they staged a
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formal debate on a single proposition, that
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the far side of the Moon should be preserved
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solely for scientific endeavors.
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Avery: And the answer is presumably not obvious or
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there'd be no debate.
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Anna: It's genuinely not. Arguing in favor were
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Joe Silk of Johns Hopkins and Jonathan
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McDowell, who most of our listeners will know
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from Jonathan's space report and who is now
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an honorary professor at Durham Space
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Research Center. After decades at the Harvard
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Smithsonian center for Astrophysica, um, and
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against M. Nikita Chu, also at Durham, who
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works on space technology governance, and
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manuel Salvoldi, an Aram space engineer with
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25 years across industry and academia.
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Barton Ward convened it. The case for
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protection rests on one physical fact. The
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far side is the only radio quiet real
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estate anywhere near Earth.
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Avery: The Moon is tidally locked, so the same
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hemisphere always faces us, which means the
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far side is permanently shielded from every
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transmitter, every radar, every broadcast on
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this planet. And that matters because.
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Anna: Because there are signals we want to detect
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that are drowned out everywhere else. The
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cosmic dark ages, the stretch of time after
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the Big Bang before the first star switched
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on. The radio emission from that era is faint
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and it's low frequency. And Earth is far too
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noisy a place to hear it. A far side radio
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telescope is arguably the only way we ever
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will.
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Avery: That's a fairly specific and, um,
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irreplaceable thing to be arguing about.
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Anna: It is, and Cilk's framing was essentially
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generational, that we should protect these
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conditions for science. That won't be done
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for decades, because the questions at stake
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are whether we're alone and how the universe
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began.
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Avery: And, um, the physical case doesn't stop at
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radio.
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Anna: No. They also argued the far side would be an
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exceptional site for gravitational wave
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detection. No atmosphere, no weather, very
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little seismic activity compared with Earth,
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and no artificial light, which is becoming a
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real problem for optical astronomy down here.
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Avery: So what's the counterargument, because leave
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it alone is easy to say.
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Anna: The counterargument is about sustainability,
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and I thought it was stronger than people
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might expect. Few's position was that this
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isn't a challenge to the value of the
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science, it's a question of how you keep
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going back at all. Lunar exploration that
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depends entirely on government funding is
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fragile. Commercial investment is what makes
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it resilient. And her argument was that you
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can have both under proper governance, that
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an inclusive CIS lunar economy on the far
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side doesn't have to turn into a free for
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all.
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Avery: Which is a fair point. A protected region
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nobody can afford to reach is protected in a
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fairly useless way.
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Anna: That's the tension. Exactly. And McDowell's
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put the stakes in the broadest possible
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terms. His line was is the whole solar system
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up for grabs or do we set aside reserves?
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Avery: That's the real question, isn't it? Not the
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Moon specifically.
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Anna: Not the Moon specifically. His argument was
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that whatever we decide in the next few years
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becomes the precedent for everything after
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Mars, the asteroids, all of it.
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Avery: Did they take a vote?
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Anna: They did. Before and after. By QR code.
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Support for the motion went from 68%
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to 76%, though the room moved
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towards protection, which, given the
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audience, isn't a shock. But an eight point
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swing after hearing both sides is a real
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result rather than a formality. And it fed
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into a full session the next day on lunar
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governance and regulation.
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Avery: And in the meantime, Chang' E6 has just
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demonstrated that the far side is
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scientifically valuable in ways nobody had
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directly measured measured until this month,
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which rather
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Anna: sharpens the argument staying at the National
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Avery: Astronomy Meeting because there is a
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genuinely extraordinary object I want to talk
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about, and it lives in our skies.
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Southern skies Puppis, which for our
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Australian and New Zealand listeners is well
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placed for a good chunk of the year, and for
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northern listeners sits low on the south. The
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object is V445 Puppis,
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and it is the only confirmed helium nova in
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the Milky Way.
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Anna: Define helium nova.
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Avery: So a nova, an ordinary nova,
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is a white dwarf in a binary system stealing
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gas off its companion. That gas piles
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up on the surface, pressure and temperature
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climb, and eventually you get a runaway
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thermonuclear explosion. It doesn't
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destroy the star, it just blows the
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accumulated layer off. And in virtually
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every case, that stolen material is
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hydrogen rich, because hydrogen is what stars
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are mostly made of.
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Anna: And this one isn't.
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Avery: This one has essentially no hydrogen at all,
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which is a very strange thing for a stellar
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explosion to be missing, given hydrogen is
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the most abundant element in the universe. So
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the obvious question is what is it stealing
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from?
341
00:13:09.240 --> 00:13:10.760
Anna: And nobody could see.
342
00:13:10.920 --> 00:13:13.134
Avery: Nobody could see. V445
343
00:13:13.306 --> 00:13:16.240
puppys erupted in late 2000, and it
344
00:13:16.240 --> 00:13:19.240
threw out an enormous bipolar outflow. Two
345
00:13:19.240 --> 00:13:21.600
lobes of material streaming in opposite
346
00:13:21.600 --> 00:13:23.640
directions, more than a trillion miles
347
00:13:23.640 --> 00:13:26.590
across. But the eruption also created a thick
348
00:13:26.590 --> 00:13:29.190
disk of dust that completely swallowed the
349
00:13:29.190 --> 00:13:32.190
system. For more than 20 years, astronomers
350
00:13:32.190 --> 00:13:34.510
could watch the debris expanding, but they
351
00:13:34.510 --> 00:13:36.830
could not see what was inside it. The dust
352
00:13:36.830 --> 00:13:39.590
has now thinned enough. John Mills, a
353
00:13:39.590 --> 00:13:41.910
researcher and PhD student at the University
354
00:13:41.910 --> 00:13:44.350
of Warwick, put together observations
355
00:13:44.350 --> 00:13:47.190
spanning two decades to finally see through
356
00:13:47.270 --> 00:13:49.270
using what a stack of instruments.
357
00:13:49.670 --> 00:13:51.870
Infrared from the Very Large Telescope in
358
00:13:51.870 --> 00:13:54.450
Chile, Optical imaging from Hubble,
359
00:13:54.690 --> 00:13:56.930
Long term spectroscopy from the Southern
360
00:13:56.930 --> 00:13:59.650
African Large Telescope and photometry from
361
00:13:59.650 --> 00:14:02.530
tess. And the answer is a white dwarf
362
00:14:02.530 --> 00:14:04.130
feeding off a helium star.
363
00:14:04.290 --> 00:14:07.050
Anna: And a helium star is a star
364
00:14:07.050 --> 00:14:09.170
Avery: that has been stripped of its outer hydrogen
365
00:14:09.170 --> 00:14:11.610
envelope, most likely by the companion it's
366
00:14:11.610 --> 00:14:14.290
now feeding. They are genuinely rare.
367
00:14:14.530 --> 00:14:16.570
The estimate is a few thousand stripped
368
00:14:16.570 --> 00:14:18.850
helium stars among the hundreds of billions
369
00:14:18.850 --> 00:14:20.770
of stars in the entire galaxy.
370
00:14:21.010 --> 00:14:23.770
Anna: So one of the rarest kinds of stars in the
371
00:14:23.770 --> 00:14:26.270
only known example of one of the rarest kinds
372
00:14:26.270 --> 00:14:26.990
of explosions.
373
00:14:27.070 --> 00:14:29.870
Avery: And it's already loading the gun again. The
374
00:14:29.870 --> 00:14:32.430
system is actively transferring material once
375
00:14:32.510 --> 00:14:35.150
more. The two stars orbit each other every
376
00:14:35.150 --> 00:14:38.070
3.7 days, which is around twice as
377
00:14:38.070 --> 00:14:39.790
long as anyone previously thought.
378
00:14:39.790 --> 00:14:41.150
Anna: You said there was a mystery.
379
00:14:41.150 --> 00:14:43.590
Avery: The bullets. The bullets embedded in the
380
00:14:43.590 --> 00:14:46.590
outflowing debris are discrete clumps of gas,
381
00:14:46.830 --> 00:14:49.310
possibly oxygen rich, though the composition
382
00:14:49.310 --> 00:14:51.870
isn't nailed down. Moving at up to 20
383
00:14:51.950 --> 00:14:54.340
million miles an hour, that's roughly
384
00:14:54.340 --> 00:14:57.100
9,000 kilometers per second, around
385
00:14:57.100 --> 00:14:58.780
3% of the speed of light.
386
00:14:59.020 --> 00:15:00.740
Anna: And nothing like that has been seen
387
00:15:00.740 --> 00:15:01.180
elsewhere.
388
00:15:01.420 --> 00:15:04.060
Avery: Nothing like it in any other nova anywhere.
389
00:15:04.300 --> 00:15:06.860
Mills suspects they formed after the outburst
390
00:15:06.860 --> 00:15:09.060
rather than during it. But as he put it,
391
00:15:09.060 --> 00:15:10.700
their origin is a mystery.
392
00:15:10.700 --> 00:15:12.940
Anna: Which is the honest answer. And I appreciate
393
00:15:12.940 --> 00:15:13.660
that he said it.
394
00:15:13.660 --> 00:15:16.540
Avery: So do I. Now, the reason this matters. Beyond
395
00:15:16.540 --> 00:15:19.180
its own strangeness, Astronomers suspect that
396
00:15:19.180 --> 00:15:21.500
repeated helium rich eruptions on a white
397
00:15:21.500 --> 00:15:23.700
dwarf might be one of the pathways that
398
00:15:23.700 --> 00:15:26.640
eventually produces a type 1A supernova.
399
00:15:26.640 --> 00:15:29.080
Anna: And type IAs are the standard candles.
400
00:15:29.400 --> 00:15:31.800
Avery: They are. They explode with remarkably
401
00:15:31.800 --> 00:15:33.600
consistent brightness, which is what makes
402
00:15:33.600 --> 00:15:35.680
them useful as distance markers across the
403
00:15:35.680 --> 00:15:38.040
universe. They're how we measured cosmic
404
00:15:38.040 --> 00:15:40.360
expansion. The work that won the Nobel Prize
405
00:15:40.360 --> 00:15:42.320
for the discovery that the expansion is
406
00:15:42.320 --> 00:15:42.920
accelerating.
407
00:15:43.320 --> 00:15:45.800
Anna: So the ruler we use to measure the universe
408
00:15:45.800 --> 00:15:48.160
depends on understanding how these things
409
00:15:48.160 --> 00:15:48.840
detonate.
410
00:15:49.000 --> 00:15:51.800
Avery: It does. And whether helium novae actually
411
00:15:51.800 --> 00:15:54.320
get there is still an open question. But
412
00:15:54.320 --> 00:15:56.960
V445 Puppis is now the clearest
413
00:15:56.960 --> 00:15:59.880
laboratory anyone has for testing it. And it
414
00:15:59.880 --> 00:16:02.240
took 25 years of dust clearing to get the
415
00:16:02.240 --> 00:16:02.720
door open.
416
00:16:03.120 --> 00:16:05.440
Anna: Last story before we look up. And it's the
417
00:16:05.440 --> 00:16:08.000
biggest one in terms of sheer scale. There's
418
00:16:08.000 --> 00:16:10.480
a case being made that the entire Milky Way
419
00:16:10.480 --> 00:16:11.600
once flipped over.
420
00:16:12.000 --> 00:16:14.640
Avery: Flipped over how exactly? Because a galaxy
421
00:16:14.640 --> 00:16:15.920
doesn't have a right way up.
422
00:16:16.080 --> 00:16:18.320
Anna: It doesn't. And that's the right instinct.
423
00:16:18.480 --> 00:16:20.640
What's being proposed is a change of
424
00:16:20.640 --> 00:16:23.200
orientation. That the disk of our galaxy
425
00:16:23.200 --> 00:16:25.670
reoriented itself by more than 90 degrees
426
00:16:26.140 --> 00:16:28.460
relative to the halo of old stars around it.
427
00:16:28.780 --> 00:16:30.620
Avery: And what put that idea on the table?
428
00:16:30.860 --> 00:16:32.620
Anna: A puzzle that's been sitting there since
429
00:16:32.620 --> 00:16:35.500
Gaia. Our galaxy has a flat disk where
430
00:16:35.500 --> 00:16:37.980
most of the stars live. And around that a
431
00:16:37.980 --> 00:16:40.860
much larger, much sparser stellar halo.
432
00:16:41.020 --> 00:16:43.420
Mostly stars that formed in smaller galaxies
433
00:16:43.420 --> 00:16:45.460
and got absorbed when those galaxies were
434
00:16:45.460 --> 00:16:47.740
Avery: pulled in debris from past meals.
435
00:16:47.980 --> 00:16:50.740
Anna: Essentially. And Gaia showed that the halo
436
00:16:50.740 --> 00:16:53.660
barely rotates. It creeps around at something
437
00:16:53.660 --> 00:16:56.540
like 10 to 20 kilometers per second. The
438
00:16:56.540 --> 00:16:58.660
disk by comparison is moving at about
439
00:16:58.660 --> 00:16:59.580
220.
440
00:17:00.140 --> 00:17:02.300
Avery: That is a very large discrepancy.
441
00:17:02.540 --> 00:17:04.820
Anna: It is. And nobody had a satisfying
442
00:17:04.820 --> 00:17:07.580
explanation. So Kirill Botrikov at
443
00:17:07.580 --> 00:17:10.060
Durham went looking for one in simulations.
444
00:17:10.060 --> 00:17:13.060
The Auriga Suite, which models Milky Way like
445
00:17:13.060 --> 00:17:15.900
galaxies in detail. He took 25 of them
446
00:17:15.980 --> 00:17:18.300
and followed their evolution across roughly
447
00:17:18.300 --> 00:17:21.130
11 billion years. And the
448
00:17:21.130 --> 00:17:23.770
galaxies that ended up with the most slowly
449
00:17:23.770 --> 00:17:26.410
rotating halos had two things in common.
450
00:17:26.410 --> 00:17:29.210
They'd experienced a major head on merger
451
00:17:29.530 --> 00:17:32.250
and their disks had reoriented by more than
452
00:17:32.250 --> 00:17:33.050
90 degrees.
453
00:17:33.450 --> 00:17:35.690
Avery: And we know we had a major head on merger.
454
00:17:35.850 --> 00:17:38.850
Anna: We do. Gaia Sausage, Enceladus. The
455
00:17:38.850 --> 00:17:41.170
collision roughly 10 billion years ago that
456
00:17:41.170 --> 00:17:43.610
dumped an enormous quantity of stars into our
457
00:17:43.610 --> 00:17:46.130
halo and is the reason the halo looks the way
458
00:17:46.130 --> 00:17:46.570
it does.
459
00:17:47.060 --> 00:17:49.140
Avery: So the proposal is that the same collision
460
00:17:49.140 --> 00:17:51.820
exerted a gravitational torque on our disk
461
00:17:51.820 --> 00:17:54.060
and slowly turned it over inside the
462
00:17:54.060 --> 00:17:55.700
surrounding dark matter halo.
463
00:17:56.020 --> 00:17:58.820
Anna: Slowly meaning over hundreds of
464
00:17:58.820 --> 00:18:00.980
millions of years. Nothing about this was
465
00:18:00.980 --> 00:18:03.220
sudden, but the end state is that the plane
466
00:18:03.220 --> 00:18:05.620
the sun orbits in today may bear no
467
00:18:05.620 --> 00:18:07.860
relationship to the plane stars were orbiting
468
00:18:07.860 --> 00:18:09.220
in before the collision.
469
00:18:09.540 --> 00:18:11.620
Avery: That does something odd to my sense of place.
470
00:18:11.860 --> 00:18:14.500
Anna: It does mine too. And I want to be careful
471
00:18:14.500 --> 00:18:16.780
here because Botcherkov himself is careful.
472
00:18:16.940 --> 00:18:19.580
His position is that a disk flip is a likely
473
00:18:19.660 --> 00:18:22.540
explanation given how slowly the halo turns,
474
00:18:22.620 --> 00:18:24.780
but that it's too early to claim it with full
475
00:18:24.780 --> 00:18:27.420
confidence. What he wants is independent
476
00:18:27.420 --> 00:18:30.260
signatures, other scars that a reorientation
477
00:18:30.260 --> 00:18:31.980
on that Scale should have left behind.
478
00:18:32.380 --> 00:18:34.060
Avery: Is there anything pointing the same way
479
00:18:34.060 --> 00:18:34.380
already?
480
00:18:34.700 --> 00:18:37.060
Anna: There is, and it's suggestive rather than
481
00:18:37.060 --> 00:18:39.660
conclusive. Separate work this year led by
482
00:18:39.660 --> 00:18:42.300
Ling Xu used the motions of more than
483
00:18:42.300 --> 00:18:45.090
600,000 giant stars from Gaia and the
484
00:18:45.240 --> 00:18:47.960
LAMOST survey to reconstruct the shape of our
485
00:18:47.960 --> 00:18:50.800
dark matter halo. And the outer halo appears
486
00:18:50.800 --> 00:18:52.690
to be oriented almost vertically relative,
487
00:18:52.690 --> 00:18:53.520
uh, to the
488
00:18:53.520 --> 00:18:56.080
Avery: stellar disk, which is what you'd expect if
489
00:18:56.080 --> 00:18:58.200
the inner part tilted and the outer part
490
00:18:58.200 --> 00:18:58.680
didn't.
491
00:18:58.920 --> 00:19:01.520
Anna: That's the reading. The outer halo kept the
492
00:19:01.520 --> 00:19:04.160
old orientation. The disk and inner halo
493
00:19:04.160 --> 00:19:06.800
swung round. Two independent lines of
494
00:19:06.800 --> 00:19:09.160
evidence converging on the same story from
495
00:19:09.160 --> 00:19:12.050
completely different data. Not proof,
496
00:19:12.370 --> 00:19:14.410
but it's the kind of thing that turns a
497
00:19:14.410 --> 00:19:17.410
curiosity into a research program. And
498
00:19:17.410 --> 00:19:19.690
I rather like that. The biggest structural
499
00:19:19.690 --> 00:19:22.490
question about our own galaxy is one we can
500
00:19:22.490 --> 00:19:25.170
only answer by looking at it from the inside.
501
00:19:25.570 --> 00:19:27.050
Avery: Right, Time to look up.
502
00:19:27.050 --> 00:19:29.410
And Anna, uh, we have actual advice today
503
00:19:29.410 --> 00:19:30.610
rather than a countdown.
504
00:19:30.930 --> 00:19:33.850
Anna: We do. And the advice is don't wait for the
505
00:19:33.850 --> 00:19:34.210
peak.
506
00:19:34.530 --> 00:19:35.170
Avery: Explain.
507
00:19:35.410 --> 00:19:38.130
Anna: The southern Delta Aquarids are running now.
508
00:19:38.520 --> 00:19:41.000
The shower is already active and it stays
509
00:19:41.000 --> 00:19:43.880
active into late August. The American Meteor
510
00:19:43.880 --> 00:19:46.680
Society puts maximum activity around the
511
00:19:46.680 --> 00:19:47.560
30th of July.
512
00:19:48.040 --> 00:19:50.520
Avery: And the problem with the 30th is the moon.
513
00:19:50.680 --> 00:19:53.400
Anna: The moon is the problem. Full moon falls on
514
00:19:53.400 --> 00:19:56.320
the 29th of July. So on peak night, you're
515
00:19:56.320 --> 00:19:59.080
looking at a sky that is something like 98%
516
00:19:59.160 --> 00:20:01.680
illuminated. That will wash out most of the
517
00:20:01.680 --> 00:20:04.560
shower. Because Delta Aquariad meteors tend
518
00:20:04.560 --> 00:20:07.400
towards long, graceful trails rather than
519
00:20:07.400 --> 00:20:09.980
bright fireballs. They're exactly the kind
520
00:20:09.980 --> 00:20:11.300
that moonlight erases.
521
00:20:11.780 --> 00:20:13.780
Avery: So the peak is the worst night of the run.
522
00:20:14.180 --> 00:20:16.900
Anna: Close to it. But here's the good news. This
523
00:20:16.900 --> 00:20:19.420
shower has no sharp maximum. It
524
00:20:19.420 --> 00:20:21.980
rambles. Rates build slowly and stay
525
00:20:21.980 --> 00:20:24.740
roughly level for well over a week. Which
526
00:20:24.740 --> 00:20:27.140
means the mornings between now and about the
527
00:20:27.140 --> 00:20:29.980
27th are better than peak night because the
528
00:20:29.980 --> 00:20:32.700
waxing gibbous moon still sets before the
529
00:20:32.700 --> 00:20:33.700
radiant gets high.
530
00:20:34.350 --> 00:20:36.630
Avery: So the window is after moonset, before
531
00:20:36.630 --> 00:20:39.550
Anna: dawn, after moonset, before dawn. That's
532
00:20:39.550 --> 00:20:41.790
your window. And it applies wherever you are.
533
00:20:41.950 --> 00:20:44.550
Where do we look? The radiant sits near the
534
00:20:44.550 --> 00:20:47.390
star Skat in Aquarius. The easiest way
535
00:20:47.390 --> 00:20:50.069
in is to find Fomalhaut bright and
536
00:20:50.069 --> 00:20:52.950
noticeably alone in a fairly empty patch of
537
00:20:52.950 --> 00:20:55.790
sky. And work from there. The Great Square of
538
00:20:55.790 --> 00:20:57.230
Pegasus helps as well.
539
00:20:57.390 --> 00:20:59.070
Avery: And, um, that's a very different experience
540
00:20:59.230 --> 00:21:01.150
depending on which hemisphere you're in.
541
00:21:01.780 --> 00:21:04.260
Anna: Completely different from Australia and New
542
00:21:04.260 --> 00:21:06.820
Zealand. The radiant climbs close to overhead
543
00:21:06.820 --> 00:21:09.620
in the pre dawn hours. This is genuinely
544
00:21:09.620 --> 00:21:11.900
our Shower. The southern part of the world
545
00:21:11.900 --> 00:21:14.820
gets the best of it every year from Sydney or
546
00:21:14.820 --> 00:21:17.219
Auckland, anywhere from about 2 in the
547
00:21:17.219 --> 00:21:18.660
morning until first light.
548
00:21:18.980 --> 00:21:21.140
Avery: And for our North American listeners, who are
549
00:21:21.140 --> 00:21:22.660
the largest part of this audience,
550
00:21:22.980 --> 00:21:25.300
Anna: you still get a good showing, but the
551
00:21:25.300 --> 00:21:27.940
radiance stays lower in the southern sky, so
552
00:21:27.940 --> 00:21:29.980
you'll see fewer of them and they'll come in
553
00:21:29.980 --> 00:21:32.580
at shallower angles. And the upside of a low
554
00:21:32.580 --> 00:21:35.460
radiant is Earth grazers, meteors that
555
00:21:35.460 --> 00:21:37.900
skim along the atmosphere and leave much
556
00:21:37.900 --> 00:21:40.620
longer trails than usual. The best hours are
557
00:21:40.620 --> 00:21:43.300
the same from around 2 in the morning local
558
00:21:43.300 --> 00:21:46.110
time, uh, until dawn. So 2 to 5am, um,
559
00:21:46.110 --> 00:21:48.500
eastern and the equivalent across Central
560
00:21:48.660 --> 00:21:49.940
Mountain and Pacific.
561
00:21:50.340 --> 00:21:52.340
Avery: And get south facing and dark.
562
00:21:52.500 --> 00:21:55.260
Anna: Get south facing, get away from lights and
563
00:21:55.260 --> 00:21:57.980
give your eyes 20 minutes to adapt before you
564
00:21:57.980 --> 00:21:58.980
judge whether it's working.
565
00:21:59.640 --> 00:22:01.640
Avery: One more thing. And, um, this one is a watch
566
00:22:01.720 --> 00:22:03.880
this space rather than a forecast.
567
00:22:04.200 --> 00:22:05.720
Anna: The sun has woken up.
568
00:22:06.120 --> 00:22:07.880
Avery: Sunspot 4493.
569
00:22:08.120 --> 00:22:10.400
Anna: That one. It appeared essentially from
570
00:22:10.400 --> 00:22:12.520
nothing over the space of a couple of days
571
00:22:12.520 --> 00:22:15.480
and grew fast. And it now has what's called
572
00:22:15.480 --> 00:22:17.800
a beta gamma delta magnetic
573
00:22:17.800 --> 00:22:20.240
classification, which is the most complex
574
00:22:20.240 --> 00:22:22.800
classification there is. Regions like that
575
00:22:22.800 --> 00:22:24.680
are, uh, where the big flares come from.
576
00:22:25.110 --> 00:22:27.600
Avery: And it's already produced some 3M M
577
00:22:27.670 --> 00:22:30.150
Anna: class flares inside a single day. The
578
00:22:30.150 --> 00:22:33.150
Strongest an M M3.4, each of
579
00:22:33.150 --> 00:22:35.710
them causing brief minor radio blackouts
580
00:22:35.710 --> 00:22:37.270
across different parts of the world.
581
00:22:37.590 --> 00:22:39.670
Forecasters have been putting the odds of
582
00:22:39.670 --> 00:22:42.150
further M M class activity at better than
583
00:22:42.150 --> 00:22:44.590
even with a smaller chance of an X class
584
00:22:44.590 --> 00:22:44.950
event.
585
00:22:45.350 --> 00:22:47.310
Avery: So it's worth keeping an eye on the aurora
586
00:22:47.310 --> 00:22:48.630
alerts it is.
587
00:22:48.950 --> 00:22:51.630
Anna: Earlier this week, a fast solar wind stream
588
00:22:51.630 --> 00:22:53.910
from a coronal hole pushed conditions to
589
00:22:53.910 --> 00:22:56.620
minor storm level, with aurora possible as
590
00:22:56.850 --> 00:22:59.530
far equatorward as Hobart in the south and
591
00:22:59.530 --> 00:23:02.210
Seattle and Edinburgh in the north. That
592
00:23:02.210 --> 00:23:04.850
particular stream is easing now. But with a
593
00:23:04.850 --> 00:23:07.490
region that complex facing us, the situation
594
00:23:07.570 --> 00:23:08.690
can change quickly.
595
00:23:09.010 --> 00:23:11.010
Avery: And Southern hemisphere observers have the
596
00:23:11.010 --> 00:23:13.009
advantage of long winter nights right now,
597
00:23:13.170 --> 00:23:15.970
while northern observers are fighting short
598
00:23:15.970 --> 00:23:18.210
summer ones. Swings and
599
00:23:18.210 --> 00:23:19.250
roundabouts.
600
00:23:19.490 --> 00:23:22.370
Anna: That's episode 148, Starship waiting
601
00:23:22.370 --> 00:23:25.260
on a window that may or may not hold, a far
602
00:23:25.260 --> 00:23:27.260
side that's been quietly recording our
603
00:23:27.260 --> 00:23:29.860
magnetic field and an argument about whether
604
00:23:29.860 --> 00:23:30.820
we should leave it alone.
605
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Avery: Plus a star that spent 25 years behind a
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curtain and the galaxy that may have rolled
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over in its sleep.
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Anna: Show notes, sources and everything else are
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at astronomydaily, IO or
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astrodaily Pod, wherever you like to find us.
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Avery: If you're up before dawn this week chasing
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00:23:46.500 --> 00:23:49.260
Delta Aquariids, we'd love to see what you
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catch.
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Anna: We'll be back tomorrow.
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Avery: Until then, clear skies.
