What Keeps a Galaxy Churning: Andromeda's Supernova Secrets Revealed

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Anna: A galaxy should be quiet. Stir

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a cloud of gas and the churning dies away in

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a few million years, like ripples going flat

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on a pond. And yet every spiral

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galaxy we look at is still churning.

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Something keeps stirring the pot.

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Avery: Today, a survey of the galaxy next door that

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catches a spoon in the act, plus the

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ghostly particles that may decide which stars

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explode at all. A planet with an expiry

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date and the sun goes blank for the first

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time since February.

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Anna: The I'm Anna.

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Avery: And I'm Avery. This is astronomy daily,

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episode 199.

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Anna: Start with a problem that has sat in the

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background of galaxy science for about 50

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years, and that has the useful quality of

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being easy to state and very hard to

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answer. The gas between the stars in a

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galaxy is turbulent. It is not sitting still

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and it is not flowing smoothly. It is

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churning on every scale from a few light

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years up to thousands, with gas moving at

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something like 10 kilometres a second

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relative to its neighbours. We have measured

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this in our own galaxy and in every nearby

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galaxy we can resolve it is simply how

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interstellar gas behaves. Here is the

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problem. Turbulence dies. That is

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the one thing turbulence reliably does.

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Energy cascades from big eddies down to

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small eddies, and at the bottom it turns into

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heat and it gone. In

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1999, an astrophysicist named

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Mordecai Mark Macklow put a number on

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how fast that happens in interstellar

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conditions. And the number was brutal.

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Turbulence in a galaxy's gas should decay

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away in roughly the time it takes the gas to

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cross itself once a few tens of

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millions of years on a galactic clock.

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That's an afternoon. So the churning

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we see should not be there unless

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something is putting the energy back

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continuously for billions of years.

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Avery: And there has never been a shortage of

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suspects.

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Anna: No shortage at all. Supernovae are

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the obvious one. But gravity itself can

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drive turbulence. As the disc shears and

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clumps, there is the magnetorotational

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instability, which wrings energy out of the

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galaxy's rotation through its magnetic field.

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There is gas falling in from outside, and

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massive stars blow winds long before they

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explode. All of these are real. The

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question was never whether supernovae

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contribute. It was whether they are enough

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on their own to pay the whole bill.

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Avery: Uh, and to answer that, you need to do

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something nobody had managed. You need to

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count the receipts. When massive stars in a

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cluster explode, and they do it in batches,

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because massive stars are born in groups and

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die within a few million years of one

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another, the blasts merge. Instead of

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a single expanding remnant you get a super

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bubble, an enormous cavity blown in the

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neutral hydrogen, its edge still pushing

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outwards. Superbubbles are the fingerprints

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each one carries in its size and its

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expansion speed, a record of how much energy

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went into it and roughly when.

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Anna: So a, uh, complete, dynamically resolved

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census of superbubbles across an entire

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galaxy would let you add up the energy

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supernovae have actually delivered and then

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compare it against how fast the turbine

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turbulence in that same galaxy is bleeding

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energy away. If the two numbers match,

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you have your answer. If supernovae falls

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short, something else is doing the work.

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Avery: Nobody had that senses for a reason. That's

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almost funny. We can't do it for the Milky

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Way because we live inside it. Mapping

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bubbles in our own galaxy is like surveying a

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forest from the base of one tree. And for

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other galaxies we have the sensitivity or the

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resolution, never both.

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Anna: Which is where two telescopes on opposite

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sides of the world come in. Exactly

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that. The paper is in Nature astronomy,

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published on 17 September. Led by

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Fan Yi Meng of Tsinghua University,

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with Zhao Wei Tsai and Jingwen Wu,

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and with D Li, Jinghua's head of

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astronomy and the former chief scientist of

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the FAST telescope as corresponding

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authority, they combined two instruments.

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FAST is the 500 metre aperture

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spherical telescope sitting in a natural

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limestone bowl in Guizhou Province in

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southern China, the most sensitive single

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dish on Earth. At these wavelengths, what it

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gives you is faint, diffuse, large

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scale structure, the outskirts of bubbles,

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the gas nobody else can see. What it

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cannot give you is fine detail. For

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that they used archival observations from the

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Jansky Very Large array in New Mexico,

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27 dishes spread across the desert.

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Working as one instrument, the array

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resolves the sharp edges fast,

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fills in everything. The array's spacing

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makes it blind to stitch them together, and

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you get a map that is both deep and sharp,

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which is exactly what this problem has always

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needed.

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Avery: They pointed that combination at Messier 31,

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the Andromeda Galaxy, the nearest big

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spiral, 2 1/2 million light years away

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and close enough that we can see the whole

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disc laid out from the outside. They mapped

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it in the 21 centimetre line of neutral

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hydrogen, the radio signal that traces

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cold atomic gas.

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Anna: From that map, they pulled

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365 candidate cavities

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and after classification, confirmed

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118 genuine super bubbles

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across the entire disc.

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Avery: And the result?

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Anna: The first thing worth noticing is the ages.

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Measured from their sizes and expansion

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speeds, the bubbles run up to 40 million

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years old. That is not an arbitrary number.

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It is almost exactly how long a star

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cluster keeps producing Supernovae from its

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first massive star dying to its last.

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The ages line up with the clock you would

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predict if clusters are uh, what makes them B

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Lee put the scale plainly. Those

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118 bubbles correspond to

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thousands of supernova explosions over the

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past 40 million years. Then the actual

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test from the bubbles they calculated the

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rate at which supernovae are injecting

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kinetic energy between 10 to the

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49th to 10 to the 51.5

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ergs per cubic kiloparsec per

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million years. Separately and this is the

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part that makes the paper work. They derived

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the rate at which turbulence is dissipating

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energy from the same data using the

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observed motions of the gastwo

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independent numbers. They match match

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how closely in magnitude. And

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this is the stronger claim in spatial

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distribution.

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It's not just that the galaxy wide totals

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happen to agree, which could be coincidence

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between two quantities that both scale with

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how many stars a ah galaxy has. It's that

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where the supernovae energy goes in is

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where the turbulent energy comes out

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region by region across the disc. The

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supply map matches the demand map.

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That's much harder to get by accent. The

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conclusion the authors draw is carefully

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worded and I want to keep their wording.

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Clustered supernova feedback is

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sufficient to sustain galactic scale

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turbulence. Why this matters beyond

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bookkeeping is turbulence is not a detail

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of galaxies, it's one of the controls.

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Turbulent pressure helps hold a ah gas disc

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up against its own gravity. And turbulence is

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what stops molecular clouds collapsing all at

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once. A large part of why galaxies

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convert gas into stars. So slowly

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change the turbulence and you change the star

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formation rate. So this closes a loop.

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Gas collapses and forms stars. The biggest

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of those stars explode. The explosions

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stir the remaining gas. The stirring

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regulates how readily the next generation

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forms. Galaxies are partly self

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governing and this is the first time both

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ends of that loop have been measured in the

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same galaxy from the same data and found

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to balance.

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Avery: And um, the caveat now the honest

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Anna: limits and there are three first,

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sufficient is not the same as sole

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showing supernovae can pay the whole bill

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does not prove nothing else. Chips in

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gravity and the magneto rotational

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instability have not been eliminated. They

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have been made unnecessary, which is a weaker

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and more interesting result. Second, this

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is neutral atomic hydrogen. It does not

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directly trace the molecular gas where

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stars actually form or the hot

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ionised gas and the energy budget in those

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phases could behave differently. And third,

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this is one galaxy, a large,

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fairly quiet spiral that has not formed stars

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vigorously in a long while. Whether the books

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balance the same way in a starburst or in a

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small, irregular, uh, galaxy where bubbles

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can blow straight out.

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The top is exactly the next question.

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Two footnotes I enjoyed Bordechai Mark

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McClo, the man whose 1999

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paper showed this turbulence should have died

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long ago, is a co author here. His own

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result is referenced too, in the paper that

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answers it. And because Nature Astronomy

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publishes its referee reports, we know one

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of the two reviewers was Christoph Federath

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at the Australian National University, who

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has spent a career on this exact question.

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The Australian fingerprint is on the scrutiny

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rather than the data. Regular listeners will

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hear an echo here. Two weeks ago we ran

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the finding that black hole outflows can

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trigger star formation as well as shut it

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down. Feedback that builds as well as

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breaks. This is the same lesson one

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rung down the letter. At stellar scale,

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feedback is not simply destructive, it is

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a galaxy's thermostat.

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Avery: Anna's Storey takes supernovae as given and

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asks what they do to a galaxy. This one

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asks a question one step which

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stars actually managed to explode? You would

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think that was settled. It is not. We

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see fewer supernovae than our models say we

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should. And there's a related puzzle, the red

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supergiant problem. When astronomers go back

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through archival images to identify the star

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that blew up, they never find 1 above about

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16 to 18 solar masses. Even

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though plenty of stars are heavier, something

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is quietly removing the most massive stars

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from the exploding population. A new paper in

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Physical Review D from Mariam Gogilashvili

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and Irene Tambora at the Niels Bohr Institute

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in Copenhagen Contorm points at an

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unlikely culprit. Neutrinos changing

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identity Quick refresher When a

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Anna: massive star's core collapses, about

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99% of the energy released leaves

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as neutrinos. And the explosion depends on

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a small fraction of that flood being

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reabsorbed by the gas just outside the

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core, heating it enough to revive the

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stalled shock wave. It's a narrow margin.

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Neutrinos also come in three flavours

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electron, muon and tau and

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oscillate between them, which is Nobel

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winning physics from 1998.

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Avery: Here's the catch. Only the electron flavour

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deposits heat efficiently. Muon and tau

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neutrinos mostly sail straight out. So

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if flavour conversion happens deep inside a

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00:11:45.210 --> 00:11:47.930
collapsing core, it takes energy earmarked

268
00:11:47.930 --> 00:11:50.210
for the explosion and redistributes it into

269
00:11:50.210 --> 00:11:52.960
flavours that simply leave. Most state of the

270
00:11:52.960 --> 00:11:55.360
art simulations leave this out on the old

271
00:11:55.360 --> 00:11:57.480
assumption that conversion happens too far

272
00:11:57.480 --> 00:11:59.840
out to matter. Recent work says

273
00:11:59.840 --> 00:12:02.760
otherwise, so Maryam Gogilashvili and

274
00:12:02.760 --> 00:12:05.720
Irene Tambora put it in schematically and

275
00:12:05.720 --> 00:12:08.600
ran the collapse of 195 stars

276
00:12:08.680 --> 00:12:11.560
from 9 to 120 solar masses

277
00:12:12.040 --> 00:12:14.960
without flavour conversion. About 27%

278
00:12:14.960 --> 00:12:17.640
of their stars fail to explode and collapse

279
00:12:17.640 --> 00:12:20.070
straight to black holes. That matches both

280
00:12:20.070 --> 00:12:22.750
the literature and observations. Switch

281
00:12:22.750 --> 00:12:25.270
flavour conversion on and the failure rate

282
00:12:25.270 --> 00:12:28.030
climbs to somewhere between 48 and

283
00:12:28.030 --> 00:12:30.830
88% depending on how deep in the

284
00:12:30.830 --> 00:12:33.430
core you let it happen. And the stars most

285
00:12:33.430 --> 00:12:36.030
affected sit between 16 and 30

286
00:12:36.030 --> 00:12:37.950
solar masses, which is

287
00:12:37.950 --> 00:12:40.750
Anna: precisely the missing mass range. In the red

288
00:12:40.750 --> 00:12:41.950
supergiant problem.

289
00:12:42.190 --> 00:12:44.990
Avery: There is a second quieter result I like more.

290
00:12:45.300 --> 00:12:47.580
And the stars that do still explode. Flavour

291
00:12:47.580 --> 00:12:50.100
conversion revives the shock earlier so less

292
00:12:50.100 --> 00:12:52.500
material rains back onto the newborn neutron

293
00:12:52.500 --> 00:12:55.300
star. The neutron stars come out lighter,

294
00:12:55.300 --> 00:12:58.180
closer to the 1.2 to 1.4 solar

295
00:12:58.180 --> 00:13:00.420
masses we actually measure in pulsars.

296
00:13:00.900 --> 00:13:03.460
A model that was running heavy now matches

297
00:13:03.940 --> 00:13:06.740
the honest handling. Here is the range. 48

298
00:13:06.740 --> 00:13:09.700
to 88% is not a measurement. It is a span

299
00:13:09.700 --> 00:13:11.860
across assumptions. And the authors say

300
00:13:11.860 --> 00:13:13.780
plainly that their upper valleys look to be

301
00:13:13.780 --> 00:13:16.380
in tension with observations. This is one

302
00:13:16.380 --> 00:13:18.380
dimensional modelling with a deliberately

303
00:13:18.380 --> 00:13:20.700
simplified switch for the neutrino physics.

304
00:13:20.860 --> 00:13:23.460
What it establishes is not a number. It is

305
00:13:23.460 --> 00:13:25.620
that this effect is too big to keep leaving

306
00:13:25.620 --> 00:13:28.420
out. The preprint went up in mid

307
00:13:28.420 --> 00:13:30.620
May, so the work has been circulating about

308
00:13:30.620 --> 00:13:32.460
four months. It is the journal version that

309
00:13:32.460 --> 00:13:32.580
is

310
00:13:32.580 --> 00:13:34.980
Anna: new and a southern footnote that is not a

311
00:13:34.980 --> 00:13:36.980
stretch. We have caught neutrinos from

312
00:13:36.980 --> 00:13:39.420
exactly one supernova SN

313
00:13:39.580 --> 00:13:42.380
1987A in the Southern Magellanic

314
00:13:42.380 --> 00:13:45.160
Cloud cloud 20 dozen particles over about 13

315
00:13:45.240 --> 00:13:47.560
seconds in February 1987.

316
00:13:48.040 --> 00:13:50.600
Every word of this debate traces back to that

317
00:13:50.600 --> 00:13:53.560
1 handful of detections from a galaxy only

318
00:13:53.560 --> 00:13:56.160
southern observers see properly. The next

319
00:13:56.160 --> 00:13:58.560
galactic supernova settles a great deal of

320
00:13:58.560 --> 00:13:58.839
it.

321
00:13:59.000 --> 00:14:00.920
Avery: Okay, moving on to storey 3.

322
00:14:01.400 --> 00:14:03.920
Most exoplanet discoveries come with an open

323
00:14:03.920 --> 00:14:06.320
ended invitation. Go and study it whenever

324
00:14:06.320 --> 00:14:08.680
you like. This one comes with a deadline.

325
00:14:09.120 --> 00:14:11.600
Published on 18 September in the publications

326
00:14:11.600 --> 00:14:14.160
of the Astronomical Society of Japan from

327
00:14:14.160 --> 00:14:16.480
Noriharu Watanabe and Norio

328
00:14:16.480 --> 00:14:18.920
Narita at the University of Tokyo with a

329
00:14:18.920 --> 00:14:21.600
large international team. The discovery of

330
00:14:21.600 --> 00:14:24.600
TOI 1355b, a

331
00:14:24.600 --> 00:14:27.360
hot Jupiter and a strange one on three counts

332
00:14:27.440 --> 00:14:30.028
count one is the star. TOI

333
00:14:30.212 --> 00:14:33.160
1355 is an A type star about twice

334
00:14:33.160 --> 00:14:36.080
the Sun's mass with a surface near 8,700

335
00:14:36.160 --> 00:14:39.120
Kelvin, um, some 3,000 degrees hotter than

336
00:14:39.120 --> 00:14:41.920
the Sun. It's around 800 light years away

337
00:14:41.920 --> 00:14:44.560
and it spins fast better than 80

338
00:14:44.560 --> 00:14:46.760
kilometres a second against our Sun's

339
00:14:46.760 --> 00:14:49.520
leisurely two count two is the

340
00:14:49.520 --> 00:14:52.360
planet. Nearly six Jupiter masses. About

341
00:14:52.360 --> 00:14:55.160
1.4 Jupiter radii whipping around

342
00:14:55.160 --> 00:14:57.560
that star every 2.17 days.

343
00:14:57.960 --> 00:15:00.120
But its orbit is not a circle. The

344
00:15:00.120 --> 00:15:03.100
eccentricity is about 0.22 a

345
00:15:03.100 --> 00:15:04.700
properly lopsided orbit.

346
00:15:04.700 --> 00:15:07.020
Anna: Why is that surprising for a hot Jupiter?

347
00:15:07.180 --> 00:15:09.700
Avery: Because they're almost never lopsided sitting

348
00:15:09.700 --> 00:15:12.340
that close in tides should round off an orbit

349
00:15:12.340 --> 00:15:15.300
quickly. Of the roughly 20 hot Jupiters known

350
00:15:15.300 --> 00:15:17.740
around hot stars, the measured eccentricities

351
00:15:17.740 --> 00:15:20.660
are essentially zero, some to four decimal

352
00:15:20.660 --> 00:15:22.460
places. And there's exactly one other

353
00:15:22.460 --> 00:15:24.980
eccentric case on record. These worlds are

354
00:15:24.980 --> 00:15:27.420
thought to be flung inward on wild elliptical

355
00:15:27.420 --> 00:15:29.820
orbits by gravitational bullying from other

356
00:15:29.820 --> 00:15:32.310
planets. Then have those orbits ground down

357
00:15:32.310 --> 00:15:34.870
to circles by tides. TOI

358
00:15:34.870 --> 00:15:37.790
1355B is partway through the grinding,

359
00:15:37.790 --> 00:15:40.590
which we rarely gets. Watch count three

360
00:15:40.590 --> 00:15:42.910
is the deadline. Comparing transits across

361
00:15:42.910 --> 00:15:45.850
TESS observations from 2019, 2020,

362
00:15:46.021 --> 00:15:48.910
2022 and 2024. The team

363
00:15:48.910 --> 00:15:50.750
found the planet crossing the star at a

364
00:15:50.750 --> 00:15:53.030
steadily different height each time. The

365
00:15:53.030 --> 00:15:55.950
orbit's plane is swinging nodal precession

366
00:15:55.950 --> 00:15:58.230
driven by the bulge of that rapidly spinning

367
00:15:58.230 --> 00:16:01.150
star. Wind it forward and the planet stops

368
00:16:01.150 --> 00:16:03.150
crossing the star's face from our point of

369
00:16:03.150 --> 00:16:05.510
view around the middle of 2033.

370
00:16:05.670 --> 00:16:08.670
Anna: After that, no transits for centuries. The

371
00:16:08.670 --> 00:16:09.670
planet is fine.

372
00:16:09.670 --> 00:16:12.430
Our line of sight is what runs out. There is

373
00:16:12.430 --> 00:16:15.109
a lovely methodological wrinkle too.

374
00:16:15.350 --> 00:16:17.990
You normally weigh a planet by watching the

375
00:16:17.990 --> 00:16:20.550
star wobble. But this star spins

376
00:16:20.710 --> 00:16:23.350
so fast its spectral lines are smeared

377
00:16:23.510 --> 00:16:26.050
and that does not work. So they weighed it

378
00:16:26.050 --> 00:16:28.410
from the light curve instead from M. The way

379
00:16:28.410 --> 00:16:31.210
the planet's gravity distorts the star into

380
00:16:31.210 --> 00:16:33.890
a faint rugby ball shape. And from the

381
00:16:33.890 --> 00:16:36.330
subtle brightening as the star is tugged

382
00:16:36.330 --> 00:16:39.170
towards us. The mass came out of the shape of

383
00:16:39.170 --> 00:16:41.890
the light, not the shift of the lines. And

384
00:16:41.890 --> 00:16:43.850
the supporting cast is worth naming.

385
00:16:44.170 --> 00:16:47.170
Alongside TESS and the 3.8 metre

386
00:16:47.170 --> 00:16:49.850
SEMI telescope in Okayama, this

387
00:16:49.850 --> 00:16:52.490
paper leans on a 91 centimetre

388
00:16:52.490 --> 00:16:55.060
telescope on the slopes of Matt Etna,

389
00:16:55.370 --> 00:16:58.090
a 40 centimetre in Switzerland and a

390
00:16:58.090 --> 00:17:00.970
28 centimetre at a private observatory in

391
00:17:00.970 --> 00:17:03.890
Germany. Backyard scale instruments on the

392
00:17:03.890 --> 00:17:06.770
Discovery paper for a six Jupiter mass

393
00:17:06.770 --> 00:17:09.730
world. The preprint went up in August, so

394
00:17:09.730 --> 00:17:12.050
about a month ahead of the journal. And for

395
00:17:12.050 --> 00:17:14.430
our southern listeners the star sits at Ah,

396
00:17:14.430 --> 00:17:17.410
Declination 67, which means

397
00:17:17.410 --> 00:17:20.130
it never rises from Sydney. Northern

398
00:17:20.130 --> 00:17:22.890
listeners can find the field in Cepheus. The

399
00:17:22.890 --> 00:17:25.690
team is already preparing a follow up on how

400
00:17:25.690 --> 00:17:27.970
tilted the orbit is and wants

401
00:17:27.970 --> 00:17:30.690
JWST time to low

402
00:17:30.690 --> 00:17:31.050
ETH

403
00:17:31.050 --> 00:17:32.730
Avery: orbit now and the business end of

404
00:17:32.730 --> 00:17:33.410
spaceflight.

405
00:17:33.570 --> 00:17:36.320
On 18 September, NASA exercised a UH

406
00:17:36.410 --> 00:17:39.330
contract modification with SpaceX for three

407
00:17:39.330 --> 00:17:41.370
additional crew rotation missions to the

408
00:17:41.370 --> 00:17:44.370
International Space Crew 1 5, Crew

409
00:17:44.370 --> 00:17:47.210
16 and Crew 1 7. The value

410
00:17:47.210 --> 00:17:50.130
is $946 million for all

411
00:17:50.130 --> 00:17:52.820
three covering ground launch in

412
00:17:52.820 --> 00:17:54.980
orbit and return and recovery operations,

413
00:17:55.460 --> 00:17:58.180
cargo on each mission and lifeboat capability

414
00:17:58.180 --> 00:18:00.940
while docked. That takes SpaceX to

415
00:18:00.940 --> 00:18:03.380
17 crew missions under the commercial crew

416
00:18:03.380 --> 00:18:06.060
transportation contract and that contract's

417
00:18:06.060 --> 00:18:08.040
running total to $5.92

418
00:18:08.240 --> 00:18:11.180
billion. Period of performance runs through

419
00:18:11.180 --> 00:18:13.540
2030 with mission readiness dates in

420
00:18:13.540 --> 00:18:16.540
2027 and 2028. NASA

421
00:18:16.540 --> 00:18:18.700
flagged its intent to buy back in May and

422
00:18:18.700 --> 00:18:21.460
calls this a sole source modification that

423
00:18:21.460 --> 00:18:23.680
does not pre further purchases later.

424
00:18:24.000 --> 00:18:26.400
Anna: One line in that release is worth reading

425
00:18:26.400 --> 00:18:29.320
carefully. NASA says the change helps

426
00:18:29.320 --> 00:18:32.240
it maintain access to the station with quote,

427
00:18:32.480 --> 00:18:34.800
two unique commercial crew industry

428
00:18:34.960 --> 00:18:37.960
partners. The award itself goes to one

429
00:18:37.960 --> 00:18:40.160
of them. The original 2014

430
00:18:40.400 --> 00:18:42.960
contracts went to both Boeing and SpaceX

431
00:18:43.280 --> 00:18:46.080
and Boeing appears in this release exactly

432
00:18:46.080 --> 00:18:48.890
once in that history. NASA does

433
00:18:48.890 --> 00:18:51.490
not say anything here about when its second

434
00:18:51.490 --> 00:18:53.050
provider next flies people.

435
00:18:53.450 --> 00:18:55.290
We'll report that when they do say.

436
00:18:55.530 --> 00:18:57.770
Avery: Meanwhile, the near term mission is moving.

437
00:18:58.090 --> 00:19:00.770
The four astronauts of Crew 13 entered

438
00:19:00.770 --> 00:19:02.770
quarantine late on Thursday at UH Johnson

439
00:19:02.770 --> 00:19:05.370
Space Centre in Houston. NASA's Jessica

440
00:19:05.370 --> 00:19:08.290
Watkins and Luke Delaney, the Canadian Space

441
00:19:08.290 --> 00:19:10.650
Agency's Yoshua Kutryk and

442
00:19:10.650 --> 00:19:12.850
Roscosmos cosmonaut Sergey

443
00:19:12.850 --> 00:19:15.630
tatariotnikov. NASA and SpaceX

444
00:19:15.630 --> 00:19:18.230
are still targeting early October. Before

445
00:19:18.230 --> 00:19:20.550
quarantine. They finished training at SpaceX

446
00:19:20.550 --> 00:19:22.910
in Hawthorne and ran a crew equipment

447
00:19:22.910 --> 00:19:25.750
interface test at Cape Canaveral. Suits on

448
00:19:25.830 --> 00:19:28.670
into the Dragon leak cheques, seat fit

449
00:19:28.670 --> 00:19:31.590
comms cheques, my favourite detail. They sit

450
00:19:31.590 --> 00:19:33.750
in the capsule and listen to its fans and

451
00:19:33.750 --> 00:19:35.790
pumps so that none of the sounds are

452
00:19:35.790 --> 00:19:37.190
unfamiliar on launch day.

453
00:19:37.430 --> 00:19:40.190
Anna: The quarantine itself is an Apollo era

454
00:19:40.190 --> 00:19:43.030
invention still doing its job. Keeping a head

455
00:19:43.030 --> 00:19:45.560
cold on the ground where it belongs. That

456
00:19:45.560 --> 00:19:47.720
closes out an arc we tracked since the

457
00:19:47.720 --> 00:19:50.280
oxidizer leak stood. Crew 13 down

458
00:19:50.600 --> 00:19:53.200
valve replaced. Crew in quarantine early

459
00:19:53.200 --> 00:19:55.560
October. We still want a date.

460
00:19:55.720 --> 00:19:57.960
Quick hit, closing a thread. We opened on

461
00:19:57.960 --> 00:20:00.520
Friday. It happened on the 18th of

462
00:20:00.520 --> 00:20:02.840
September. The earth facing sun went

463
00:20:02.840 --> 00:20:05.720
completely spotless. No numbered active

464
00:20:05.720 --> 00:20:08.600
regions at all. It's the first spotless day

465
00:20:08.600 --> 00:20:11.160
since the 24th of February and the

466
00:20:11.160 --> 00:20:13.640
19th was spotless too, making it two in a

467
00:20:13.640 --> 00:20:16.330
row. By the 20th, a small new region

468
00:20:16.330 --> 00:20:19.250
had rotated up and the run ended. Which is

469
00:20:19.250 --> 00:20:21.770
exactly how the descent from a solar maximum

470
00:20:21.770 --> 00:20:24.370
goes. Not a switch, but a flicker that

471
00:20:24.370 --> 00:20:27.090
Avery: lengthens for scale on how far we have come

472
00:20:27.090 --> 00:20:27.450
down.

473
00:20:27.690 --> 00:20:30.570
The busiest single day of the Solar cycle

474
00:20:30.570 --> 00:20:33.450
was 8 August 2024, with

475
00:20:33.450 --> 00:20:35.730
an estimated 337

476
00:20:35.730 --> 00:20:38.610
sunspots. That was the highest daily count

477
00:20:38.610 --> 00:20:41.520
since March 2001. Cycle

478
00:20:41.520 --> 00:20:44.000
25 peaked in late 2024

479
00:20:44.240 --> 00:20:46.560
and minimum is not expected before about

480
00:20:46.560 --> 00:20:47.280
2030.

481
00:20:47.520 --> 00:20:50.360
Anna: But do not put the aurora gear away. A

482
00:20:50.360 --> 00:20:53.080
coronal hole is rotating into position and

483
00:20:53.080 --> 00:20:55.360
its fast solar wind stream should reach us

484
00:20:55.360 --> 00:20:58.280
around the 23rd, with forecasters flagging a

485
00:20:58.280 --> 00:21:01.160
chance of minor geomagnetic storming. If

486
00:21:01.160 --> 00:21:03.680
it lands, best chances are the far north,

487
00:21:03.920 --> 00:21:06.440
northern Scotland and the far south, southern

488
00:21:06.440 --> 00:21:09.120
New Zealand. It arrives right on the equinox,

489
00:21:09.120 --> 00:21:11.480
which is the most aurora friendly moment of

490
00:21:11.480 --> 00:21:14.320
the year. For reasons of geometry and the

491
00:21:14.320 --> 00:21:16.600
standing point we keep making. A, uh, quiet

492
00:21:16.600 --> 00:21:19.520
sun means fewer auroras, but it also means

493
00:21:19.520 --> 00:21:22.400
a weaker shield against galactic cosmic rays.

494
00:21:22.640 --> 00:21:25.600
So that background quietly rises same

495
00:21:25.600 --> 00:21:27.880
dial opposite end to the sky.

496
00:21:27.880 --> 00:21:30.000
Avery: And this week the calendar does something

497
00:21:30.000 --> 00:21:32.320
that only makes sense if you remember. The

498
00:21:32.320 --> 00:21:35.050
Earth is tilted first to equinox,

499
00:21:35.130 --> 00:21:37.810
five minutes past midnight universal time on

500
00:21:37.810 --> 00:21:40.730
the 23rd. An equinox is an instant,

501
00:21:40.730 --> 00:21:43.570
not a day. So where you stand decides the

502
00:21:43.570 --> 00:21:45.570
date. That is Tuesday evening in the

503
00:21:45.570 --> 00:21:48.250
Americas, just after five in Los Angeles,

504
00:21:48.410 --> 00:21:50.930
just after eight in New York, one in the

505
00:21:50.930 --> 00:21:53.650
morning in London and five past ten on

506
00:21:53.650 --> 00:21:56.170
Wednesday morning in Sydney. Spring here,

507
00:21:56.330 --> 00:21:58.490
autumn there, same instant.

508
00:21:58.810 --> 00:22:01.570
Anna: Then on Saturday the 26th, the full

509
00:22:01.570 --> 00:22:04.420
moon, the harvest moon. The full moon falling

510
00:22:04.420 --> 00:22:07.220
closest to the September equinox. And here's

511
00:22:07.220 --> 00:22:09.140
where it gets interesting. Because the

512
00:22:09.140 --> 00:22:11.700
harvest moon's entire reputation is a

513
00:22:11.700 --> 00:22:13.340
northern hemisphere phenomenon.

514
00:22:13.580 --> 00:22:15.380
Avery: Explain that, because I think most people

515
00:22:15.380 --> 00:22:16.780
assume it's just a name.

516
00:22:17.020 --> 00:22:19.740
Anna: It's not just a name. The moon Normally

517
00:22:19.740 --> 00:22:22.220
rises about 50 minutes later each night.

518
00:22:22.460 --> 00:22:24.500
Around the northern autumn equinox. The

519
00:22:24.500 --> 00:22:26.940
Moon's path meets the eastern horizon at a

520
00:22:26.940 --> 00:22:29.700
shallow angle. So successive moon rises,

521
00:22:29.700 --> 00:22:32.420
bunch up and you get several evenings running

522
00:22:32.420 --> 00:22:34.540
with bright moonlight arriving just after

523
00:22:34.540 --> 00:22:37.440
sunset, which was the whole point. Extra

524
00:22:37.440 --> 00:22:38.760
light to finish the harvest.

525
00:22:39.000 --> 00:22:41.280
Avery: We ran the numbers for this week. On the

526
00:22:41.280 --> 00:22:44.080
nights around full moon, moonrise comes later

527
00:22:44.080 --> 00:22:46.520
by about 12 minutes a night. In London,

528
00:22:46.760 --> 00:22:49.680
22 minutes in New York, 27 in Los

529
00:22:49.680 --> 00:22:51.480
Angeles and in Sydney,

530
00:22:51.880 --> 00:22:53.320
62 minutes.

531
00:22:53.800 --> 00:22:56.440
Anna: So we get the opposite of a harvest moon.

532
00:22:56.600 --> 00:22:59.600
Avery: We get the anti harvest moon. The effect the

533
00:22:59.600 --> 00:23:01.840
thing is named for is more than five times

534
00:23:01.840 --> 00:23:04.600
weaker here than in London. Same moon,

535
00:23:04.680 --> 00:23:07.680
same week, geometry simply reversed. In

536
00:23:07.680 --> 00:23:10.520
spring it's the same ecliptic angle that

537
00:23:10.520 --> 00:23:13.280
gives us a brilliant high Venus and one

538
00:23:13.280 --> 00:23:14.440
hugging the horizon.

539
00:23:14.760 --> 00:23:17.480
One wrinkle for Australian listeners The full

540
00:23:17.480 --> 00:23:20.120
moon Instant lands at 2:48 on Sunday

541
00:23:20.120 --> 00:23:22.800
morning our time, so our calendars say

542
00:23:22.800 --> 00:23:25.040
27th and northern ones say

543
00:23:25.040 --> 00:23:27.560
26th. It looks full on both nights.

544
00:23:27.720 --> 00:23:28.600
Anna: And the planets?

545
00:23:28.840 --> 00:23:30.960
Avery: Venus is still the show in the west after

546
00:23:30.960 --> 00:23:33.720
sunset. At uh magnitude -4.5

547
00:23:34.430 --> 00:23:37.350
from Sydney it stands 37 degrees high as

548
00:23:37.350 --> 00:23:40.070
the sun sets and hangs on for more than three

549
00:23:40.070 --> 00:23:42.750
hours. From New York, 13 degrees

550
00:23:42.990 --> 00:23:45.790
from London, 2 1/2 degrees about

551
00:23:45.790 --> 00:23:48.670
25 minutes with a dead flat western horizon

552
00:23:48.990 --> 00:23:51.990
in the north. Look early and low through a

553
00:23:51.990 --> 00:23:54.630
telescope. It's a big thin crescent, a

554
00:23:54.630 --> 00:23:57.390
quarter lit but 42 arcseconds across.

555
00:23:57.870 --> 00:24:00.560
Larger than Jupiter's disc. Below it

556
00:24:00.560 --> 00:24:03.400
Mercury is having a genuinely good Southern

557
00:24:03.400 --> 00:24:05.200
apparition. Magnitude

558
00:24:05.977 --> 00:24:08.880
0.2, 18 degrees up from Sydney

559
00:24:08.880 --> 00:24:11.440
at sunset and setting an hour and a half

560
00:24:11.440 --> 00:24:14.280
after the Sun. From London it's 3 degrees

561
00:24:14.280 --> 00:24:16.800
up and effectively out of reach for the

562
00:24:16.800 --> 00:24:17.080
north.

563
00:24:17.160 --> 00:24:19.760
Anna: The compensation is the morning at the start

564
00:24:19.760 --> 00:24:22.720
of nautical Twilight. Mars stands 49

565
00:24:22.720 --> 00:24:25.600
degrees high from Los Angeles, 47 from

566
00:24:25.600 --> 00:24:28.390
New York, 42 from London and just

567
00:24:28.390 --> 00:24:30.990
21 from Sydney. Jupiter is

568
00:24:30.990 --> 00:24:33.790
28 degrees up from Los Angeles against 10

569
00:24:33.790 --> 00:24:34.390
from here.

570
00:24:34.710 --> 00:24:37.350
The pre dawn sky belongs to the north right

571
00:24:37.350 --> 00:24:39.350
now and it is worth getting up for.

572
00:24:39.830 --> 00:24:42.590
Saturn rises mid evening and is highest

573
00:24:42.590 --> 00:24:45.230
just after midnight, better than 50 degrees

574
00:24:45.230 --> 00:24:47.590
up from Sydney at magnitude plus

575
00:24:47.590 --> 00:24:50.430
0.3. It is heading for opposition

576
00:24:50.430 --> 00:24:53.270
in early October and you will see listings

577
00:24:53.270 --> 00:24:55.390
disagree about the date. Some um, say the

578
00:24:55.390 --> 00:24:57.720
fourth, some the fifth. Both are right.

579
00:24:58.040 --> 00:25:00.680
Opposition measured by ecliptic longitude

580
00:25:00.680 --> 00:25:03.480
falls on the 4th, measured by right ascension

581
00:25:03.480 --> 00:25:06.360
the 5th. Saturn's brightness and size are

582
00:25:06.360 --> 00:25:08.920
identical across that whole week so you

583
00:25:08.920 --> 00:25:11.400
cannot pick the wrong night and our lead

584
00:25:11.400 --> 00:25:13.760
storey. Can anyone actually see

585
00:25:13.760 --> 00:25:14.600
Andromeda?

586
00:25:15.000 --> 00:25:17.560
Avery: Depends entirely where you are. From New

587
00:25:17.560 --> 00:25:19.960
York, Andromeda passes almost overhead,

588
00:25:20.200 --> 00:25:23.040
89 degrees up around half past one in the

589
00:25:23.040 --> 00:25:25.870
morning from Los Angeles, 83 from

590
00:25:25.870 --> 00:25:28.670
London, 80 from Sydney. It scrapes to

591
00:25:28.670 --> 00:25:31.470
under 15 degrees low in the north through the

592
00:25:31.470 --> 00:25:34.230
thickest part of our atmosphere. Binocular is

593
00:25:34.230 --> 00:25:36.590
in a clear northern horizon after midnight

594
00:25:36.590 --> 00:25:39.190
we'll find it but it is a smudge rather than

595
00:25:39.190 --> 00:25:41.790
the showpiece. It is up north which is the

596
00:25:41.790 --> 00:25:44.110
storey of tonight really. The north gets the

597
00:25:44.110 --> 00:25:46.750
deep sky, the predawn planets and the lunar

598
00:25:46.750 --> 00:25:49.390
occultation of Jupiter on 6 October

599
00:25:49.550 --> 00:25:51.950
that sits below our horizon entirely.

600
00:25:52.570 --> 00:25:55.130
We get Venus, Mercury and the better half of

601
00:25:55.130 --> 00:25:56.010
the geometry.

602
00:25:56.250 --> 00:25:57.930
Some weeks it runs the other way

603
00:25:58.250 --> 00:26:00.490
Anna: and the standing reminder because we are

604
00:26:00.490 --> 00:26:03.010
talking about a sun with almost nothing on it

605
00:26:03.010 --> 00:26:05.610
and people will be tempted to look. Never

606
00:26:05.610 --> 00:26:07.930
look at the sun without proper protection.

607
00:26:08.250 --> 00:26:10.930
Solar viewers and eclipse glasses must meet

608
00:26:10.930 --> 00:26:11.850
the ISO

609
00:26:12.090 --> 00:26:14.650
123122

610
00:26:14.970 --> 00:26:17.530
international safety standard, and that is

611
00:26:17.530 --> 00:26:20.130
not the same as ordinary sunglasses, no

612
00:26:20.130 --> 00:26:22.410
matter how dark they are. And stacking

613
00:26:22.410 --> 00:26:24.160
sunglasses does not help.

614
00:26:24.560 --> 00:26:26.800
Cheque your filters for damage before use,

615
00:26:26.880 --> 00:26:29.600
and discard any that are scratched, punctured

616
00:26:29.600 --> 00:26:32.280
or peeling. If you're using a telescope or

617
00:26:32.280 --> 00:26:34.840
binoculars, the filter goes on the front of

618
00:26:34.840 --> 00:26:37.640
the instrument, never on the eyepiece, where

619
00:26:37.640 --> 00:26:39.600
focused sunlight can crack it without

620
00:26:39.600 --> 00:26:42.600
warning. There is no safe way to improvise

621
00:26:42.600 --> 00:26:42.880
this.

622
00:26:43.600 --> 00:26:45.600
Avery: That's astronomy daily for today.

623
00:26:45.920 --> 00:26:48.920
118 Bubbles in Andromeda that bounce a

624
00:26:48.920 --> 00:26:51.700
galaxy's energy books neutrinos that may

625
00:26:51.700 --> 00:26:53.900
quietly decide which stars are allowed to

626
00:26:53.900 --> 00:26:56.100
explode a planet. We have until

627
00:26:56.100 --> 00:26:58.460
2033 to study three more

628
00:26:58.460 --> 00:27:00.540
dragonflights on the books and a crew in

629
00:27:00.540 --> 00:27:03.420
quarantine and a sun with nothing on its face

630
00:27:03.420 --> 00:27:05.140
for the first time since February.

631
00:27:05.540 --> 00:27:08.020
Anna: A note for tomorrow this was episode

632
00:27:08.020 --> 00:27:10.740
199, which makes the next one

633
00:27:10.740 --> 00:27:13.380
200, and we would like to mark it

634
00:27:13.380 --> 00:27:15.460
properly. If there's a storey from this

635
00:27:15.460 --> 00:27:17.620
series you want revisited or a question

636
00:27:17.620 --> 00:27:20.180
you've been sitting on the contact form at

637
00:27:20.180 --> 00:27:22.880
astronomydaily IO is the place.

638
00:27:23.120 --> 00:27:25.600
We do read them, and listener questions have

639
00:27:25.600 --> 00:27:27.440
set our running order more than once.

640
00:27:27.920 --> 00:27:29.880
Avery: All our sources are linked in the show notes,

641
00:27:29.880 --> 00:27:32.280
as always, along with the full references for

642
00:27:32.280 --> 00:27:33.120
today's papers.

643
00:27:33.280 --> 00:27:36.280
You'll find us at astronomydaily IO until

644
00:27:36.280 --> 00:27:36.880
tomorrow.

645
00:27:36.880 --> 00:27:37.840
Anna: Clear skies.

646
00:27:49.370 --> 00:27:50.010
The storeys.

647
00:27:57.850 --> 00:27:58.490
Avery: Were told.