Anna: The side of the Moon we never see has been
quietly keeping a secret about our own
planet. And this week, two very different
groups of scientists arrived at the same
place from opposite directions.
Avery: One group read it out of the dirt. The other
argued about who gets to own it.
Anna: Meanwhile, a rocket sits on a pad in South
Texas waiting for a second chance.
Avery: And a star that vanished behind its own
wreckage 25 years ago has finally
stepped back into the light.
Anna: Welcome to Astronomy Daily. I'm Ana.
Avery: And I'm, um. Avery. It's Thursday 23rd
July 2026, and this is episode
148.
Anna: Coming up, Starship gets another go with
a caveat. What the far side of the Moon knows
about Earth's magnetic field, whether that
far side should be off limits to industry. A
one of a kind stellar explosion finally
identified. And the possibility that our
entire galaxy once turned over.
Avery: Uh, plus a skywatch closer with some
genuinely useful advice about the Delta
Aquarids, which is to not wait for the peak.
Anna: Let's get into it.
Avery: We start at Starbase, because today is meant
to be the day.
Anna: SpaceX is targeting Flight 13 of
Starship with a 90 minute launch window that
opens at 6:45 in the evening Eastern
Time. That's 5:45 Central and
3:45 in the afternoon on the Pacific coast.
For those of us on this side of the world,
that lands at a quarter to nine on Friday
morning Australian Eastern Time and a quarter
to 11 Friday morning in New Zealand.
Avery: So North America gets it over dinner and we
get it over breakfast for once, nobody has to
set an alarm for three in the morning for
once.
Anna: Although, and this is the part I want to be
upfront about, that schedule is not locked.
Meaning? Meaning the public schedule says
today, but the road and beach closure
notifications around Starbase suggest
additional testing is happening happening on
Pad 2. Those closure notices are one of the
more reliable tells in this business because
they have to be filed in advance and they
tend to reflect what's actually planned
rather than what's been announced. So there
is a realistic chance this
Avery: slides again, which would make it the third
date for Flight 13.
Anna: It would. Let's recap how we got here because
the arc matters. Flight 13 was first set
for Thursday 16th July. The countdown went
all the way to zero and then stopped. The
flight software triggered an automatic abort
right at T0 because four of the 33
Raptor engines on the Super Heavy booster
failed to reach acceptable starting
parameters.
Avery: And um, the threshold is 3, so
Anna: it missed by exactly one engine. That's the
system working as designed and it protected
both the vehicle and the pad. Elon Musk said
afterwards that two Raptors would be pulled
and replaced before the next attempt.
Avery: That's a remarkably narrow margin between a
scrub and a launch.
Anna: It is, and it's deliberate. The vehicle was
cleared to fly in the first place because the
SAA closed out its mishap investigation into
Flight 12 on 13 July. And the
booster had already completed a full duration
static fire of all 33 engines back on the
10th.
Avery: So the hardware had been through its paces.
It just didn't like the moment.
Anna: That's about the size of it. Here's what
makes this flight worth paying attention to.
Beyond the launch itself, Blight 13 is
carrying 20 V3 Starlink satellites,
the next generation of the Constellation, and
the first time Starship has ever deployed
them.
Avery: That's the whole point of the vehicle
eventually. Not the spectacle, the payload.
Anna: Right up to now, these have been test flights
carrying simulators and mass models. This is
the first time the thing does the job it was
built for. Even on a suborbital trajectory
and the flight profile. Oster and ship
separate as usual. Super Heavy steers
itself to a controlled splashdown in the Gulf
about seven minutes after liftoff. No
catch attempt with the chopstick arms on this
one. The ship continues on,
deploys the satellites and then comes down
for its own splashdown in the Indian Ocean
off the coast of Western Australia at around
65
Avery: minutes, which is worth flagging for our, uh,
listeners in Perth and along that coast. You
are not going to see it from the beach. It's
a long way offshore, but it is your patch of
ocean.
Anna: It is. And for anyone in North America
hoping to catch the launch itself, it's a
star based departure. So the viewing sites
around Boca Chica and South Padre island are
the ones that matter.
Avery: So assuming it goes.
Anna: Assuming it goes. If you're listening to this
on Thursday, check before you commit your
evening. If you're listening later, you
already know how it turned out and we'll pick
up the result in the next episode. Either
way, this ark has taught us not to get ahead
of ourselves.
Avery: Now, to the moon and to something I find
genuinely lovely about this next result,
which is that it turns lunar soil into a
record of Earth.
Anna: Go on.
Avery: The sun blows a continuous stream of charged
particles out across a solar system. The
solar wind. The moon has no atmosphere and
no global magnetic field to speak of. So
those particles hit the surface directly and
bury themselves in the soil over billions of
years. The regolith becomes an archive of
everything that struck it.
Anna: And noble gases are the good bookkeepers.
Avery: Exactly. Helium, neon, argon,
krypton, xenon. They don't react with
anything. So whatever went in stays in.
And how deep it went tells you how fast it
was traveling when it arrived.
Anna: So what did they find?
Avery: A team at the Chinese Academy of Sciences,
Institute of Geology and Physics analyzed
samples from Chang' E6. The mission that
returned material from the far side from the
south pole aitken Basin. That's
1,935 grams of soil,
just under 2 kilograms.
Anna: And that's the first far side material anyone
has ever had in a laboratory.
Avery: Every previous return sample, Apollo, Luna,
Chang' e5 came from the near side. So this
is the first time anyone could directly
compare the two hemispheres. They worked
through seven portions using stepwise heating
and laser extraction, measuring the isotopes
of all five noble gases. And the far side
soil is measurably different. The solar
wind went in faster and went in deeper.
Anna: Deeper, meaning higher energy.
Avery: Higher energy, yes. The clearest signal was
in neon. The ratio of Neon 20 to
Neon 22 in the Cheng' E6 material
sits below anything recorded in any near
sight sample, which points to stronger
processing on the way in. And the heavier
gases krypton and xenon come out of the
sample at different temperatures than they do
from Chang' E5 material, which is another way
of reading implantation depth.
Anna: So why would the far side get hit harder?
Avery: Because we're in the way. M
Earth magnetosphere. As the moon
travels around its orbit, it spends part of
each month downstream of Earth, inside the
long magnetic tail our planet trails behind
it. And in that region, the solar wind
gets slowed down before it reaches the lunar
surface. But it's the near side that's facing
us. So the near side is the one that catches
at the celerated wind. The far side is
permanently turned away and takes the full
unmoderated stream.
Anna: Earth has been sheltering the side of the
moon that looks at us for 4 billion
years.
Avery: For 4 billion years. And the team put
a number on it. Roughly a quarter of the
total solar wind exposure at the Chang' e 5
landing site involved that slowed down flow.
At the Chang' e 6 site on the far side,
there's no sign of it at all.
Anna: That's a beautiful result. And I assume it
cuts the other way as well.
Avery: That's the part that excites me most. If the
near site soil records how much shielding
Earth was providing, then heavy noble gases
in lunar Regolith become a fossil record of
our own magnetosphere. Combine that with the
rock magnetism record on Earth, and you have
a completely new way of reconstructing how
our magnetic field has changed over deep
time.
Anna: Which is not a small thing, given the
magnetosphere is the reason we still have an
atmosphere.
Avery: Not a small thing at all. The Moon has been
keeping notes on us, and it turns out the far
side has the cleaner copy. Which, as
it happens, is exactly why a room full of
astronomers spent Tuesday evening arguing
about what we're allowed to do out there.
Anna: So this was at the Royal Astronomical
Society's National Astronomy Meeting, which
is running this week at the University of
Birmingham. On Tuesday evening, they staged a
formal debate on a single proposition, that
the far side of the Moon should be preserved
solely for scientific endeavors.
Avery: And the answer is presumably not obvious or
there'd be no debate.
Anna: It's genuinely not. Arguing in favor were
Joe Silk of Johns Hopkins and Jonathan
McDowell, who most of our listeners will know
from Jonathan's space report and who is now
an honorary professor at Durham Space
Research Center. After decades at the Harvard
Smithsonian center for Astrophysica, um, and
against M. Nikita Chu, also at Durham, who
works on space technology governance, and
manuel Salvoldi, an Aram space engineer with
25 years across industry and academia.
Barton Ward convened it. The case for
protection rests on one physical fact. The
far side is the only radio quiet real
estate anywhere near Earth.
Avery: The Moon is tidally locked, so the same
hemisphere always faces us, which means the
far side is permanently shielded from every
transmitter, every radar, every broadcast on
this planet. And that matters because.
Anna: Because there are signals we want to detect
that are drowned out everywhere else. The
cosmic dark ages, the stretch of time after
the Big Bang before the first star switched
on. The radio emission from that era is faint
and it's low frequency. And Earth is far too
noisy a place to hear it. A far side radio
telescope is arguably the only way we ever
will.
Avery: That's a fairly specific and, um,
irreplaceable thing to be arguing about.
Anna: It is, and Cilk's framing was essentially
generational, that we should protect these
conditions for science. That won't be done
for decades, because the questions at stake
are whether we're alone and how the universe
began.
Avery: And, um, the physical case doesn't stop at
radio.
Anna: No. They also argued the far side would be an
exceptional site for gravitational wave
detection. No atmosphere, no weather, very
little seismic activity compared with Earth,
and no artificial light, which is becoming a
real problem for optical astronomy down here.
Avery: So what's the counterargument, because leave
it alone is easy to say.
Anna: The counterargument is about sustainability,
and I thought it was stronger than people
might expect. Few's position was that this
isn't a challenge to the value of the
science, it's a question of how you keep
going back at all. Lunar exploration that
depends entirely on government funding is
fragile. Commercial investment is what makes
it resilient. And her argument was that you
can have both under proper governance, that
an inclusive CIS lunar economy on the far
side doesn't have to turn into a free for
all.
Avery: Which is a fair point. A protected region
nobody can afford to reach is protected in a
fairly useless way.
Anna: That's the tension. Exactly. And McDowell's
put the stakes in the broadest possible
terms. His line was is the whole solar system
up for grabs or do we set aside reserves?
Avery: That's the real question, isn't it? Not the
Moon specifically.
Anna: Not the Moon specifically. His argument was
that whatever we decide in the next few years
becomes the precedent for everything after
Mars, the asteroids, all of it.
Avery: Did they take a vote?
Anna: They did. Before and after. By QR code.
Support for the motion went from 68%
to 76%, though the room moved
towards protection, which, given the
audience, isn't a shock. But an eight point
swing after hearing both sides is a real
result rather than a formality. And it fed
into a full session the next day on lunar
governance and regulation.
Avery: And in the meantime, Chang' E6 has just
demonstrated that the far side is
scientifically valuable in ways nobody had
directly measured measured until this month,
which rather
Anna: sharpens the argument staying at the National
Avery: Astronomy Meeting because there is a
genuinely extraordinary object I want to talk
about, and it lives in our skies.
Southern skies Puppis, which for our
Australian and New Zealand listeners is well
placed for a good chunk of the year, and for
northern listeners sits low on the south. The
object is V445 Puppis,
and it is the only confirmed helium nova in
the Milky Way.
Anna: Define helium nova.
Avery: So a nova, an ordinary nova,
is a white dwarf in a binary system stealing
gas off its companion. That gas piles
up on the surface, pressure and temperature
climb, and eventually you get a runaway
thermonuclear explosion. It doesn't
destroy the star, it just blows the
accumulated layer off. And in virtually
every case, that stolen material is
hydrogen rich, because hydrogen is what stars
are mostly made of.
Anna: And this one isn't.
Avery: This one has essentially no hydrogen at all,
which is a very strange thing for a stellar
explosion to be missing, given hydrogen is
the most abundant element in the universe. So
the obvious question is what is it stealing
from?
Anna: And nobody could see.
Avery: Nobody could see. V445
puppys erupted in late 2000, and it
threw out an enormous bipolar outflow. Two
lobes of material streaming in opposite
directions, more than a trillion miles
across. But the eruption also created a thick
disk of dust that completely swallowed the
system. For more than 20 years, astronomers
could watch the debris expanding, but they
could not see what was inside it. The dust
has now thinned enough. John Mills, a
researcher and PhD student at the University
of Warwick, put together observations
spanning two decades to finally see through
using what a stack of instruments.
Infrared from the Very Large Telescope in
Chile, Optical imaging from Hubble,
Long term spectroscopy from the Southern
African Large Telescope and photometry from
tess. And the answer is a white dwarf
feeding off a helium star.
Anna: And a helium star is a star
Avery: that has been stripped of its outer hydrogen
envelope, most likely by the companion it's
now feeding. They are genuinely rare.
The estimate is a few thousand stripped
helium stars among the hundreds of billions
of stars in the entire galaxy.
Anna: So one of the rarest kinds of stars in the
only known example of one of the rarest kinds
of explosions.
Avery: And it's already loading the gun again. The
system is actively transferring material once
more. The two stars orbit each other every
3.7 days, which is around twice as
long as anyone previously thought.
Anna: You said there was a mystery.
Avery: The bullets. The bullets embedded in the
outflowing debris are discrete clumps of gas,
possibly oxygen rich, though the composition
isn't nailed down. Moving at up to 20
million miles an hour, that's roughly
9,000 kilometers per second, around
3% of the speed of light.
Anna: And nothing like that has been seen
elsewhere.
Avery: Nothing like it in any other nova anywhere.
Mills suspects they formed after the outburst
rather than during it. But as he put it,
their origin is a mystery.
Anna: Which is the honest answer. And I appreciate
that he said it.
Avery: So do I. Now, the reason this matters. Beyond
its own strangeness, Astronomers suspect that
repeated helium rich eruptions on a white
dwarf might be one of the pathways that
eventually produces a type 1A supernova.
Anna: And type IAs are the standard candles.
Avery: They are. They explode with remarkably
consistent brightness, which is what makes
them useful as distance markers across the
universe. They're how we measured cosmic
expansion. The work that won the Nobel Prize
for the discovery that the expansion is
accelerating.
Anna: So the ruler we use to measure the universe
depends on understanding how these things
detonate.
Avery: It does. And whether helium novae actually
get there is still an open question. But
V445 Puppis is now the clearest
laboratory anyone has for testing it. And it
took 25 years of dust clearing to get the
door open.
Anna: Last story before we look up. And it's the
biggest one in terms of sheer scale. There's
a case being made that the entire Milky Way
once flipped over.
Avery: Flipped over how exactly? Because a galaxy
doesn't have a right way up.
Anna: It doesn't. And that's the right instinct.
What's being proposed is a change of
orientation. That the disk of our galaxy
reoriented itself by more than 90 degrees
relative to the halo of old stars around it.
Avery: And what put that idea on the table?
Anna: A puzzle that's been sitting there since
Gaia. Our galaxy has a flat disk where
most of the stars live. And around that a
much larger, much sparser stellar halo.
Mostly stars that formed in smaller galaxies
and got absorbed when those galaxies were
Avery: pulled in debris from past meals.
Anna: Essentially. And Gaia showed that the halo
barely rotates. It creeps around at something
like 10 to 20 kilometers per second. The
disk by comparison is moving at about
220.
Avery: That is a very large discrepancy.
Anna: It is. And nobody had a satisfying
explanation. So Kirill Botrikov at
Durham went looking for one in simulations.
The Auriga Suite, which models Milky Way like
galaxies in detail. He took 25 of them
and followed their evolution across roughly
11 billion years. And the
galaxies that ended up with the most slowly
rotating halos had two things in common.
They'd experienced a major head on merger
and their disks had reoriented by more than
90 degrees.
Avery: And we know we had a major head on merger.
Anna: We do. Gaia Sausage, Enceladus. The
collision roughly 10 billion years ago that
dumped an enormous quantity of stars into our
halo and is the reason the halo looks the way
it does.
Avery: So the proposal is that the same collision
exerted a gravitational torque on our disk
and slowly turned it over inside the
surrounding dark matter halo.
Anna: Slowly meaning over hundreds of
millions of years. Nothing about this was
sudden, but the end state is that the plane
the sun orbits in today may bear no
relationship to the plane stars were orbiting
in before the collision.
Avery: That does something odd to my sense of place.
Anna: It does mine too. And I want to be careful
here because Botcherkov himself is careful.
His position is that a disk flip is a likely
explanation given how slowly the halo turns,
but that it's too early to claim it with full
confidence. What he wants is independent
signatures, other scars that a reorientation
on that Scale should have left behind.
Avery: Is there anything pointing the same way
already?
Anna: There is, and it's suggestive rather than
conclusive. Separate work this year led by
Ling Xu used the motions of more than
600,000 giant stars from Gaia and the
LAMOST survey to reconstruct the shape of our
dark matter halo. And the outer halo appears
to be oriented almost vertically relative,
uh, to the
Avery: stellar disk, which is what you'd expect if
the inner part tilted and the outer part
didn't.
Anna: That's the reading. The outer halo kept the
old orientation. The disk and inner halo
swung round. Two independent lines of
evidence converging on the same story from
completely different data. Not proof,
but it's the kind of thing that turns a
curiosity into a research program. And
I rather like that. The biggest structural
question about our own galaxy is one we can
only answer by looking at it from the inside.
Avery: Right, Time to look up.
And Anna, uh, we have actual advice today
rather than a countdown.
Anna: We do. And the advice is don't wait for the
peak.
Avery: Explain.
Anna: The southern Delta Aquarids are running now.
The shower is already active and it stays
active into late August. The American Meteor
Society puts maximum activity around the
30th of July.
Avery: And the problem with the 30th is the moon.
Anna: The moon is the problem. Full moon falls on
the 29th of July. So on peak night, you're
looking at a sky that is something like 98%
illuminated. That will wash out most of the
shower. Because Delta Aquariad meteors tend
towards long, graceful trails rather than
bright fireballs. They're exactly the kind
that moonlight erases.
Avery: So the peak is the worst night of the run.
Anna: Close to it. But here's the good news. This
shower has no sharp maximum. It
rambles. Rates build slowly and stay
roughly level for well over a week. Which
means the mornings between now and about the
27th are better than peak night because the
waxing gibbous moon still sets before the
radiant gets high.
Avery: So the window is after moonset, before
Anna: dawn, after moonset, before dawn. That's
your window. And it applies wherever you are.
Where do we look? The radiant sits near the
star Skat in Aquarius. The easiest way
in is to find Fomalhaut bright and
noticeably alone in a fairly empty patch of
sky. And work from there. The Great Square of
Pegasus helps as well.
Avery: And, um, that's a very different experience
depending on which hemisphere you're in.
Anna: Completely different from Australia and New
Zealand. The radiant climbs close to overhead
in the pre dawn hours. This is genuinely
our Shower. The southern part of the world
gets the best of it every year from Sydney or
Auckland, anywhere from about 2 in the
morning until first light.
Avery: And for our North American listeners, who are
the largest part of this audience,
Anna: you still get a good showing, but the
radiance stays lower in the southern sky, so
you'll see fewer of them and they'll come in
at shallower angles. And the upside of a low
radiant is Earth grazers, meteors that
skim along the atmosphere and leave much
longer trails than usual. The best hours are
the same from around 2 in the morning local
time, uh, until dawn. So 2 to 5am, um,
eastern and the equivalent across Central
Mountain and Pacific.
Avery: And get south facing and dark.
Anna: Get south facing, get away from lights and
give your eyes 20 minutes to adapt before you
judge whether it's working.
Avery: One more thing. And, um, this one is a watch
this space rather than a forecast.
Anna: The sun has woken up.
Avery: Sunspot 4493.
Anna: That one. It appeared essentially from
nothing over the space of a couple of days
and grew fast. And it now has what's called
a beta gamma delta magnetic
classification, which is the most complex
classification there is. Regions like that
are, uh, where the big flares come from.
Avery: And it's already produced some 3M M
Anna: class flares inside a single day. The
Strongest an M M3.4, each of
them causing brief minor radio blackouts
across different parts of the world.
Forecasters have been putting the odds of
further M M class activity at better than
even with a smaller chance of an X class
event.
Avery: So it's worth keeping an eye on the aurora
alerts it is.
Anna: Earlier this week, a fast solar wind stream
from a coronal hole pushed conditions to
minor storm level, with aurora possible as
far equatorward as Hobart in the south and
Seattle and Edinburgh in the north. That
particular stream is easing now. But with a
region that complex facing us, the situation
can change quickly.
Avery: And Southern hemisphere observers have the
advantage of long winter nights right now,
while northern observers are fighting short
summer ones. Swings and
roundabouts.
Anna: That's episode 148, Starship waiting
on a window that may or may not hold, a far
side that's been quietly recording our
magnetic field and an argument about whether
we should leave it alone.
Avery: Plus a star that spent 25 years behind a
curtain and the galaxy that may have rolled
over in its sleep.
Anna: Show notes, sources and everything else are
at astronomydaily, IO or
astrodaily Pod, wherever you like to find us.
Avery: If you're up before dawn this week chasing
Delta Aquariids, we'd love to see what you
catch.
Anna: We'll be back tomorrow.
Avery: Until then, clear skies.