The Unifying Mystery of Black Hole Jets: Stellar and Supermassive Connections

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Language: en

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Take a black hole 10 times the mass of


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the sun. Now take one 10 million times


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heavier. The kind that sits in the


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middle of a galaxy and anchors a 100


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billion stars. Those two objects have


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almost nothing in common. Different


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sizes, different neighborhoods,


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different life stories. One of them you


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could fit inside a city. The other one


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you could pour the entire inner solar


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system into and still have room. And


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this week, a team led out of Perth has


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shown that when it comes to the single


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most dramatic thing a black hole does,


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firing a jet of material out into space


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at close to the speed of light, both of


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them wait for exactly the same moment.


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>> Same trigger, same threshold, seven


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orders of magnitude apart.


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>> Hello and welcome to Astronomy Daily.


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I'm Anna.


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>> And I'm Avery. It's Friday, the 18th of


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September, 2026, and this is episode


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197.


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>> So, let's start with the thing that


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makes this hard. Black holes don't emit


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anything themselves. What we actually


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see is the material falling in. It piles


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up into a disc. It heats up through


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friction until it's glowing across the


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electromagnetic spectrum. And then


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sometimes, not always, but sometimes,


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some of it gets flung back out in a


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narrow, tightly columnated jet.


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>> And the question of when you get a jet


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and when you don't, has been open for


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decades.


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>> It has. But for one class of black hole,


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we actually have a very good answer.


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Stellar mass black holes, the ones left


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behind when a massive star collapses,


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maybe 5 to 20 times the sun's mass,


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often sit in binary systems, pulling


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material off a companion star. And those


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systems cycle. They brighten, they fade,


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they go through what astronomers call


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state transitions. And they do it over


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weeks and months,


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>> which means we've watched the whole


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process start to finish many times over.


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many many times. And what we've learned


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is that the jets switch on and off at


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particular points in that cycle. And


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those points are tied to how fast the


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black hole is feeding, measured against


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something called the Edington limit.


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>> And this is worth spelling out because


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everything else today rests on it.


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>> It really does. So material falling


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toward a black hole gets extremely hot


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and hot material radiates. That


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radiation pushes outward. gravity pulls


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inward. The Edington limit is the point


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where those two balance, where the


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radiation coming off the infalling


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material is pushing outward just as hard


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as the black hole's gravity is pulling


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in.


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>> So if you try to feed a black hole


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faster than that, the radiation starts


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blowing the meal away.


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>> Anna, roughly, yes. Though nature has


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ways around it, and we'll come back to


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that. The useful thing about the


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Edington limit is that it scales with


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mass. A black hole a million times


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heavier has a limit a million times


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higher. So instead of talking about


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absolute brightness, astronomers talk in


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fractions of Edington, 10% of Edington,


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1% of Edington. And that gives you a way


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to compare black holes of wildly


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different sizes on the same scale.


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>> Which brings us to the super massive


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black holes. And the reason this has


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been so stubborn,


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>> the reason is simply time. Everything


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about an accretion flow scales with the


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mass of the black hole and that includes


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how fast it evolves. A stellar mass


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system cycles in months. A super massive


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black hole in an ordinary active galaxy


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takes something on the order of


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thousands of years to do the equivalent.


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>> So you can't watch one. You get a single


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frame of a film that runs for millennia.


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>> Exactly that. You can look at thousands


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of active galaxies and take a census.


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Here's one with a jet. Here's one


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without. But you can never watch a


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single object cross a threshold and see


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what happens. Which means the critical


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accretion rates that we know so


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precisely for stellar mass black holes


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have simply been unmeasurable for the


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big ones.


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>> Unless something gives a super massive


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black hole a sudden well-defined meal.


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>> And that's the move. Tidal disruption


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events. A star wanders too close to the


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super massive black hole at the center


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of its galaxy. The difference in


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gravitational pull across the star


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exceeds what's holding the star together


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and it comes apart. Roughly half the


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debris gets flung away and the other


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half falls back and builds a brand new


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accretion disc from nothing.


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>> And that one plays out fast,


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>> years, not millennia. You get to watch


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an accretion flow around a super massive


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black hole be born, rise, peak, and


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decline. And you can do it inside a


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single research career. That is the


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entire reason this result was possible.


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>> So Dr. Adele Goodwin at Curtain


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University's International Center for


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Radioastronomy Research in Perth, who's


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also a forest research foundation


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fellow, working with Dr. Andrew Mumry at


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the Institute for Advanced Study in


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Princeton, published in Nature Astronomy


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yesterday, Thursday the 17th of


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September.


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>> And what they show is that title


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disruption events actually launch


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outflows twice in two physically


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distinct episodes. The first comes early


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while the black hole is feeding above


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its Edington limit. That brief ferocious


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phase right after the star comes apart


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when there's far more material trying to


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get in than the black hole can


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comfortably swallow.


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>> The prompt outflow,


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>> the prompt one. And then later,


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sometimes months or years later, there's


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a second separate outflow. And that one


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arrives as the accretion rate falls


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through a specific value about 2% of the


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Edington limit.


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>> 2%. And that number is familiar. That


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number is the same critical accretion


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rate at which stellar mass black holes


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in binaries make their state


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transitions. The same value we've


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measured over and over in objects


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millions of times smaller. Goodwin and


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Mumy are arguing that the coupling


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between how a black hole feeds and how


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it throws material back out is scale


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invariant. That it doesn't care about


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mass at all


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>> across roughly seven orders of


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magnitude.


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>> Which, if it holds, is a genuinely


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unifying statement about a class of


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object we usually treat as two separate


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populations.


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>> And it also clears up a mess, doesn't


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it? Because radio astronomers have had


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an awkward problem with these events for


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a while.


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>> A very awkward one. Some title


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disruption events produce a radio flare


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almost immediately. Some produce one


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much later out of nowhere. Sometimes


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years after everyone has stopped paying


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attention. Some appear to produce


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nothing at all. That looked like three


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different phenomena or worse like noise.


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>> And the two outflow picture makes it one


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phenomenon. one phenomenon with two


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stages where whether you see either of


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them depends on when you happen to be


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looking and how the accretion rate was


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falling. The prompt and delayed outflows


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stop being a puzzle and start being a


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prediction.


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>> And Goodwin makes a very practical point


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about that.


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>> She does and it's my favorite part of


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the release. Her line is quote, "Radio


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telescopes are incredibly powerful, but


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knowing when to look is just as


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important as knowing where to look." And


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she goes on, "If we can anticipate when


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a black hole is more likely to launch a


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jet, we can run better targeted


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campaigns, waste fewer observations, and


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improve our chances of catching these


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rare events at the moment they matter


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most,


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>> which is not a small thing when you're


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competing for time on the world's big


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dishes.


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>> It's the difference between a survey and


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a stakeout. And it matters enormously


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for what's coming because the Vera Rubin


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Observatory is about to start finding


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tidal disruption events in numbers we've


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never had before. If you can look at the


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optical light curve and predict roughly


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when the radio outflow should arrive,


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you can have the radio telescopes ready.


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Without that, you're guessing.


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>> And this one is properly ours.


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>> It is led from Curtain University in


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Perth through. And the underlying data


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set is the product of years of


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multi-wavelength campaigns drawing on


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telescopes in Australia, the United


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States, India, South Africa, and in


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space. This is not a single instrument


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result. It's a decade of patient radio


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follow-up on rare events assembled into


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one picture. And it lands in the same


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week that we're talking about the square


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kilometer arrays southern half taking


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shape out in Western Australia,


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>> which is precisely the instrument you'd


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want pointed at the next one.


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>> Two things to keep straight, though.


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>> Yes. The first is that this is a


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threshold, not a switch. saying black


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holes launch outflows at around 2% of


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Eddington is a statement about where the


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transition sits, not a promise that


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every black hole crossing that line will


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produce a jet you can detect. Whether


00:09:21.839 --> 00:09:23.590
you actually see one depends on the


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environment, the geometry, the distance,


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and the luck of having a telescope


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pointed in the right direction.


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>> And the second,


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>> the second is about timing. And we want


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to be straight with you. This was


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published in Nature Astronomy yesterday.


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That's real and the peer review is done.


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But the preprint went up on the archive


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back in February. So while this is newly


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published, it is not newly written. And


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if it feels vaguely familiar to anyone


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who follows the preprint servers


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closely, that's why.


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>> Which is a pattern we've flagged before


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on this show.


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>> It is, and we'll keep flagging it. The


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science is no less good for having


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waited seven months in review, but


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published this week and discovered this


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week are different claims, and we try


00:10:08.320 --> 00:10:10.230
very hard not to blur them.


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>> Longtime listeners will hear some


00:10:11.680 --> 00:10:13.590
threads here, too. We covered a


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wandering black hole revealed by a tidal


00:10:15.839 --> 00:10:19.269
disruption event back in episode 153 and


00:10:19.279 --> 00:10:21.670
a quazar driving turbulence across


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300,000 lightyear in 154. and the


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partial disruptions that fade and come


00:10:27.360 --> 00:10:31.190
back in episode 185. This result is the


00:10:31.200 --> 00:10:33.030
framework those individual objects have


00:10:33.040 --> 00:10:34.389
been waiting for.


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>> Now on to story two. That phrase super


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Edington came up in the lead and it's


00:10:40.240 --> 00:10:42.150
about to come up again because the


00:10:42.160 --> 00:10:44.310
second story this week is also about a


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black hole eating faster than it should


00:10:46.480 --> 00:10:49.590
be able to just 11 billion years


00:10:49.600 --> 00:10:50.630
earlier.


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>> The little red dots.


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>> The little red dots. And if you've been


00:10:54.880 --> 00:10:56.710
with us a while, you'll know these have


00:10:56.720 --> 00:10:58.630
been one of the most irritating things


00:10:58.640 --> 00:11:01.990
the James Web Space Telescope has found.


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Extremely compact, extremely red,


00:11:05.360 --> 00:11:07.190
extremely numerous in the early


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universe. They show the broad hydrogen


00:11:09.920 --> 00:11:12.069
emission lines you'd expect from gas


00:11:12.079 --> 00:11:14.630
whipping around a black hole, but there


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are far too many of them. And the black


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holes implied are far too heavy for the


00:11:19.279 --> 00:11:21.030
galaxies they sit in,


00:11:21.040 --> 00:11:23.030
>> which has produced a small industry of


00:11:23.040 --> 00:11:25.190
explanations. Some of them fairly


00:11:25.200 --> 00:11:26.310
exotic,


00:11:26.320 --> 00:11:30.069
>> some very exotic. So, here's what's new.


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A team led by Sunyan Chon with Shingo


00:11:33.120 --> 00:11:36.870
Hiano, Tommoaki Ishyama, Sukjun Chang,


00:11:36.880 --> 00:11:39.509
and Vulkar Springle published in Nature


00:11:39.519 --> 00:11:42.389
on the 16th of September ran fully


00:11:42.399 --> 00:11:44.949
cosmological radiation hydrodnamic


00:11:44.959 --> 00:11:47.670
simulations of a dense protocluster


00:11:47.680 --> 00:11:50.150
region in the early universe using


00:11:50.160 --> 00:11:53.350
Japan's Aeroi3 supercomput.


00:11:53.360 --> 00:11:55.030
>> And crucially, without putting the


00:11:55.040 --> 00:11:56.630
answer in by hand,


00:11:56.640 --> 00:11:58.949
>> that's the point. They didn't seed the


00:11:58.959 --> 00:12:00.870
simulation with the black holes they


00:12:00.880 --> 00:12:03.509
wanted. They let the physics run. And


00:12:03.519 --> 00:12:06.310
what happens is this. In that intensely


00:12:06.320 --> 00:12:08.949
overdense environment, the giant gas


00:12:08.959 --> 00:12:11.670
clouds are bathed in so much ultraviolet


00:12:11.680 --> 00:12:14.230
radiation that they can't fragment into


00:12:14.240 --> 00:12:17.190
ordinary stars. Normally, a big cloud


00:12:17.200 --> 00:12:19.350
breaks up into lots of little stellar


00:12:19.360 --> 00:12:22.710
nurseries. Here it can't. So instead,


00:12:22.720 --> 00:12:25.829
the whole thing collapses as one object,


00:12:25.839 --> 00:12:28.629
a primordial super massive star, which


00:12:28.639 --> 00:12:30.949
then promptly collapses into a black


00:12:30.959 --> 00:12:32.150
hole.


00:12:32.160 --> 00:12:33.509
>> A heavy seed,


00:12:33.519 --> 00:12:36.230
>> a heavy seed of around a million solar


00:12:36.240 --> 00:12:38.629
masses, which is roughly 10 times


00:12:38.639 --> 00:12:41.269
heavier than theory typically expects.


00:12:41.279 --> 00:12:43.430
And then those seeds develop dense,


00:12:43.440 --> 00:12:46.310
optically thick discs, so thick that


00:12:46.320 --> 00:12:48.470
light bounces around inside them,


00:12:48.480 --> 00:12:50.710
scattering off free electrons on the way


00:12:50.720 --> 00:12:53.670
out. And that electron scattering smears


00:12:53.680 --> 00:12:56.230
the hydrogen emission into exactly the


00:12:56.240 --> 00:12:59.670
broad lines we see in little red dots.


00:12:59.680 --> 00:13:01.590
>> So the broad lines aren't necessarily


00:13:01.600 --> 00:13:03.590
telling you the gas is moving as fast as


00:13:03.600 --> 00:13:04.710
you'd assumed.


00:13:04.720 --> 00:13:07.030
>> That's the elegant bit. Part of the


00:13:07.040 --> 00:13:10.230
width is scattering, not velocity. and


00:13:10.240 --> 00:13:12.870
then sustained super Edington accretion


00:13:12.880 --> 00:13:15.350
drives the thing up to around 30 million


00:13:15.360 --> 00:13:18.150
solar masses by a red shift of eight


00:13:18.160 --> 00:13:20.470
which puts it right in the population of


00:13:20.480 --> 00:13:23.750
over massive quazars web keeps finding.


00:13:23.760 --> 00:13:27.190
So it's one continuous story. Seed dot


00:13:27.200 --> 00:13:30.069
quazar and eventually the super massive


00:13:30.079 --> 00:13:32.790
black holes sitting in galaxies today.


00:13:32.800 --> 00:13:35.509
>> One story with the little red dot phase


00:13:35.519 --> 00:13:38.470
being short and dust shrouded, a stage


00:13:38.480 --> 00:13:41.110
rather than a species. And the timing is


00:13:41.120 --> 00:13:43.670
rather lovely because Nature Astronomy


00:13:43.680 --> 00:13:45.910
published a whole focus issue on little


00:13:45.920 --> 00:13:48.710
red dots the same week, including a


00:13:48.720 --> 00:13:51.269
review by Hannah Ubler on massive black


00:13:51.279 --> 00:13:54.150
holes in the first billion years. The


00:13:54.160 --> 00:13:56.470
field is consolidating and this happens


00:13:56.480 --> 00:13:58.389
to be the week it did it.


00:13:58.399 --> 00:14:00.310
>> One caution though, and it's the same


00:14:00.320 --> 00:14:02.230
one we gave for the black hole feedback


00:14:02.240 --> 00:14:03.590
work last month.


00:14:03.600 --> 00:14:04.629
>> Go on.


00:14:04.639 --> 00:14:06.870
>> This is a simulation that reproduces the


00:14:06.880 --> 00:14:09.030
observations. That's a demonstration


00:14:09.040 --> 00:14:11.269
that the physics is sufficient. You


00:14:11.279 --> 00:14:13.030
don't need anything exotic to get little


00:14:13.040 --> 00:14:16.310
red dots. It is not on its own proof


00:14:16.320 --> 00:14:18.629
that this is what actually happened.


00:14:18.639 --> 00:14:21.269
Other roots may also produce them. What


00:14:21.279 --> 00:14:23.189
would settle it is a direct measurement


00:14:23.199 --> 00:14:25.030
of one of these objects that


00:14:25.040 --> 00:14:27.189
distinguishes scattering broadened lines


00:14:27.199 --> 00:14:29.430
from genuinely fast gas,


00:14:29.440 --> 00:14:31.509
>> which is exactly the kind of thing Web


00:14:31.519 --> 00:14:32.629
could do.


00:14:32.639 --> 00:14:35.030
>> Right. Next up, let's come all the way


00:14:35.040 --> 00:14:38.150
back. about 6,000 kilometers in fact to


00:14:38.160 --> 00:14:39.509
the middle of the Earth,


00:14:39.519 --> 00:14:41.670
>> which is not where you think it is.


00:14:41.680 --> 00:14:43.509
>> It really isn't. And this is one of


00:14:43.519 --> 00:14:45.110
those facts that sounds like a trick


00:14:45.120 --> 00:14:47.350
until you sit with it. There are two


00:14:47.360 --> 00:14:49.350
different centers of the Earth. There's


00:14:49.360 --> 00:14:51.509
the center of figure, the geometric


00:14:51.519 --> 00:14:53.670
middle of the solid planet surface,


00:14:53.680 --> 00:14:56.150
which is essentially fixed. And there's


00:14:56.160 --> 00:14:58.550
the center of mass, the balance point of


00:14:58.560 --> 00:15:00.550
everything the planet is made of.


00:15:00.560 --> 00:15:02.629
>> And the planet is partly made of water


00:15:02.639 --> 00:15:04.310
and air, which move


00:15:04.320 --> 00:15:07.269
>> constantly. Snow falls across Siberia


00:15:07.279 --> 00:15:10.870
and Canada. The Amazon basin floods. The


00:15:10.880 --> 00:15:13.590
monsoon arrives over Southeast Asia.


00:15:13.600 --> 00:15:15.750
Every one of those shifts an enormous


00:15:15.760 --> 00:15:17.590
amount of mass from one part of the


00:15:17.600 --> 00:15:19.829
planet to another. And the balance point


00:15:19.839 --> 00:15:22.230
moves to follow it. So the center of


00:15:22.240 --> 00:15:24.150
mass and the center of figure drift


00:15:24.160 --> 00:15:25.990
apart and back together over the course


00:15:26.000 --> 00:15:26.870
of a year.


00:15:26.880 --> 00:15:28.550
>> And we care because


00:15:28.560 --> 00:15:30.150
>> because the center of mass is what


00:15:30.160 --> 00:15:32.949
satellites orbit. It's the origin of the


00:15:32.959 --> 00:15:35.030
reference frame that underpins satellite


00:15:35.040 --> 00:15:37.990
navigation and every precise elevation


00:15:38.000 --> 00:15:40.069
measurement on the planet. If you're


00:15:40.079 --> 00:15:41.910
wrong about where it is, you're wrong


00:15:41.920 --> 00:15:44.150
about where everything else is.


00:15:44.160 --> 00:15:46.150
>> So, how big is the wobble?


00:15:46.160 --> 00:15:48.629
>> That's the news. The traditional figure


00:15:48.639 --> 00:15:52.069
has been around 11 mm. A team led by


00:15:52.079 --> 00:15:54.230
Donald Argus at NASA's Jet Propulsion


00:15:54.240 --> 00:15:57.110
Laboratory now puts it at roughly 4 to


00:15:57.120 --> 00:16:00.790
5, about half what we thought. published


00:16:00.800 --> 00:16:03.030
in Geoysical Journal International with


00:16:03.040 --> 00:16:04.870
the JPL release on Tuesday.


00:16:04.880 --> 00:16:07.030
>> Half is a big correction for something


00:16:07.040 --> 00:16:09.189
people have been measuring for decades.


00:16:09.199 --> 00:16:11.829
>> It is. And here's how uncertain it's


00:16:11.839 --> 00:16:14.069
been. The last two international


00:16:14.079 --> 00:16:16.870
estimates, one from 2017 and one from


00:16:16.880 --> 00:16:20.069
2023, disagree with each other by about


00:16:20.079 --> 00:16:23.030
7 mm, which is almost as large as the


00:16:23.040 --> 00:16:24.790
entire motion they're trying to measure.


00:16:24.800 --> 00:16:27.110
>> So, the error bar was the same size as


00:16:27.120 --> 00:16:29.430
the signal. Essentially,


00:16:29.440 --> 00:16:31.990
Argus' own line is that the movement now


00:16:32.000 --> 00:16:34.310
looks like about half of what we


00:16:34.320 --> 00:16:37.110
believed 8 years ago, and that the mass


00:16:37.120 --> 00:16:39.269
of water and air sloshing between the


00:16:39.279 --> 00:16:42.550
hemispheres is smaller than we thought.


00:16:42.560 --> 00:16:44.389
>> And where does the movement actually


00:16:44.399 --> 00:16:45.110
come from?


00:16:45.120 --> 00:16:47.749
>> Three main contributors, ocean,


00:16:47.759 --> 00:16:51.670
atmosphere, and land water. In March,


00:16:51.680 --> 00:16:53.749
snow sitting across Eurasia and North


00:16:53.759 --> 00:16:56.790
America pulls the center of mass about 3


00:16:56.800 --> 00:16:59.590
millimeters toward the northern pole.


00:16:59.600 --> 00:17:01.990
Then in April, the Amazon hits its


00:17:02.000 --> 00:17:05.110
annual water maximum, around 2,400


00:17:05.120 --> 00:17:08.630
gatons, and tugs at roughly 2.2 mm


00:17:08.640 --> 00:17:10.710
towards South America. Later in the


00:17:10.720 --> 00:17:12.549
year, monsoon water across Southeast


00:17:12.559 --> 00:17:15.350
Asia peaks at around 600 gatons and


00:17:15.360 --> 00:17:16.870
pulls in its own direction.


00:17:16.880 --> 00:17:18.069
>> None of which wins.


00:17:18.079 --> 00:17:21.029
>> None of which wins. They combine into an


00:17:21.039 --> 00:17:23.669
annual oscillation that never settles.


00:17:23.679 --> 00:17:25.429
And my favorite complication in the


00:17:25.439 --> 00:17:27.829
whole study is this. When you pile


00:17:27.839 --> 00:17:29.590
trillions of tons of water onto a


00:17:29.600 --> 00:17:32.310
continent, the crust flexes under the


00:17:32.320 --> 00:17:34.630
load, which means the ground stations


00:17:34.640 --> 00:17:36.390
you're using to measure the movement are


00:17:36.400 --> 00:17:37.590
themselves moving.


00:17:37.600 --> 00:17:39.430
>> You have to subtract the observatory


00:17:39.440 --> 00:17:41.190
from the observation.


00:17:41.200 --> 00:17:43.590
>> You do. They handled it by combining


00:17:43.600 --> 00:17:45.830
laser ranging to satellites. And that's


00:17:45.840 --> 00:17:48.150
the Legios technique which Australia


00:17:48.160 --> 00:17:49.990
contributes to from the Mount Stromlo


00:17:50.000 --> 00:17:53.029
station outside Canberra with GPS and


00:17:53.039 --> 00:17:55.510
with the Grace follow-on gravity mission


00:17:55.520 --> 00:17:58.230
then modeling the custal deformation out


00:17:58.240 --> 00:17:59.750
>> and the practical end of it.


00:17:59.760 --> 00:18:02.150
>> Felix Lander, one of the co-authors put


00:18:02.160 --> 00:18:03.990
it well. He said that while these


00:18:04.000 --> 00:18:06.470
movements might appear tiny, our modern


00:18:06.480 --> 00:18:08.470
world relies on extremely accurate


00:18:08.480 --> 00:18:10.710
positioning and that by understanding


00:18:10.720 --> 00:18:13.029
what changes the reference system, we


00:18:13.039 --> 00:18:15.270
can build better reference systems. He


00:18:15.280 --> 00:18:16.870
lists the beneficiaries as everything


00:18:16.880 --> 00:18:18.710
from global shipping logistics to


00:18:18.720 --> 00:18:20.470
precision agriculture,


00:18:20.480 --> 00:18:22.950
>> which is a long way from black holes.


00:18:22.960 --> 00:18:25.590
And I rather like that about this job.


00:18:25.600 --> 00:18:26.870
>> Me, too.


00:18:26.880 --> 00:18:29.190
>> Last story. And it's a small, clever


00:18:29.200 --> 00:18:32.150
one. 20 light years away, there's an


00:18:32.160 --> 00:18:36.310
object called SIMP0136.


00:18:36.320 --> 00:18:39.190
It's a brown dwarf, too heavy to be a


00:18:39.200 --> 00:18:41.909
planet in the ordinary sense, too light


00:18:41.919 --> 00:18:44.710
to have ever ignited hydrogen fusion and


00:18:44.720 --> 00:18:47.669
become a star. It sits right on the


00:18:47.679 --> 00:18:51.190
boundary and it has no host star at all.


00:18:51.200 --> 00:18:52.950
It's just drifting,


00:18:52.960 --> 00:18:56.070
>> which makes it unusually easy to study,


00:18:56.080 --> 00:18:59.270
>> enormously easier. Normally, if you want


00:18:59.280 --> 00:19:01.990
to look at a giant planet's atmosphere,


00:19:02.000 --> 00:19:03.909
you're fighting the glare of the star


00:19:03.919 --> 00:19:07.110
next to it. Here there's no star. You


00:19:07.120 --> 00:19:09.590
just point and look. Which is why


00:19:09.600 --> 00:19:12.310
SIMP0136


00:19:12.320 --> 00:19:14.549
has become the reference object for what


00:19:14.559 --> 00:19:16.870
directly imaged giant planets are


00:19:16.880 --> 00:19:18.070
probably like.


00:19:18.080 --> 00:19:19.590
>> And it varies.


00:19:19.600 --> 00:19:22.710
>> It spins once every 2 hours and 25


00:19:22.720 --> 00:19:25.510
minutes. And as it spins, its brightness


00:19:25.520 --> 00:19:28.630
changes by a few%. Different amounts at


00:19:28.640 --> 00:19:30.710
different wavelengths, which tells you


00:19:30.720 --> 00:19:33.669
there's weather, clouds, hotspots,


00:19:33.679 --> 00:19:35.909
chemistry, all of it changing as


00:19:35.919 --> 00:19:38.630
different faces rotate into view. The


00:19:38.640 --> 00:19:39.990
trouble has been that it's looked


00:19:40.000 --> 00:19:42.470
fantastically complicated. Multiple


00:19:42.480 --> 00:19:45.190
mechanisms, multiple layers, all tangled


00:19:45.200 --> 00:19:46.150
together.


00:19:46.160 --> 00:19:47.990
>> So, what did they do differently?


00:19:48.000 --> 00:19:51.110
>> They stopped assuming. Merl Schrader, a


00:19:51.120 --> 00:19:54.150
PhD candidate at Trinity College Dublin


00:19:54.160 --> 00:19:56.310
with colleagues there and elsewhere,


00:19:56.320 --> 00:19:58.390
took one full rotation of web


00:19:58.400 --> 00:20:01.270
spectroscopy and ran principal component


00:20:01.280 --> 00:20:03.909
analysis on it, which is a technique for


00:20:03.919 --> 00:20:06.470
asking a data set the blunt question,


00:20:06.480 --> 00:20:08.789
how many independent things are actually


00:20:08.799 --> 00:20:11.909
changing here, not does my model fit,


00:20:11.919 --> 00:20:14.870
just how many knobs are being turned?


00:20:14.880 --> 00:20:17.029
>> And the answer was


00:20:17.039 --> 00:20:19.909
>> two. Two components are enough to push


00:20:19.919 --> 00:20:22.070
what's left over down to the noise floor


00:20:22.080 --> 00:20:24.070
of the instrument. Which means that


00:20:24.080 --> 00:20:26.390
within what web can detect, there is


00:20:26.400 --> 00:20:28.149
nothing else going on.


00:20:28.159 --> 00:20:29.750
>> And what are the two?


00:20:29.760 --> 00:20:32.390
>> The first is broadband. It moves the


00:20:32.400 --> 00:20:34.470
whole spectrum together and that's


00:20:34.480 --> 00:20:37.190
temperature. The second is chromatic


00:20:37.200 --> 00:20:39.830
wavelength dependent and that traces the


00:20:39.840 --> 00:20:42.310
vertical structure of the clouds, how


00:20:42.320 --> 00:20:45.029
high and how thick they are. And between


00:20:45.039 --> 00:20:47.510
them, those two resolve into three


00:20:47.520 --> 00:20:49.990
recurring conditions. Patches that are


00:20:50.000 --> 00:20:52.310
hotter with thinner cloud, patches that


00:20:52.320 --> 00:20:54.149
are cooler with thick vertically


00:20:54.159 --> 00:20:56.950
extended cloud, and transitional regions


00:20:56.960 --> 00:20:58.230
between the two.


00:20:58.240 --> 00:21:00.149
>> So it looks chaotic and it's actually


00:21:00.159 --> 00:21:01.029
organized.


00:21:01.039 --> 00:21:04.070
>> Lowdimensional is the term. A famously


00:21:04.080 --> 00:21:06.310
messy atmosphere turns out to be running


00:21:06.320 --> 00:21:09.110
on two dials. And the team then went


00:21:09.120 --> 00:21:11.430
further and projected model atmospheres


00:21:11.440 --> 00:21:14.230
into the same mathematical space. and


00:21:14.240 --> 00:21:16.789
found the models largely occupy the same


00:21:16.799 --> 00:21:19.270
territory, which is a decent sign the


00:21:19.280 --> 00:21:21.350
models are capturing the right physics


00:21:21.360 --> 00:21:24.070
rather than accidentally agreeing.


00:21:24.080 --> 00:21:26.070
>> Two notes of care on this one,


00:21:26.080 --> 00:21:26.950
>> please.


00:21:26.960 --> 00:21:28.789
>> The first is that some of the coverage


00:21:28.799 --> 00:21:30.390
has described these patterns as


00:21:30.400 --> 00:21:32.390
persisting over more than a dozen


00:21:32.400 --> 00:21:35.430
rotations. The paper's core analysis is


00:21:35.440 --> 00:21:37.750
one rotation. That's a real and


00:21:37.760 --> 00:21:39.590
interesting result, but a second


00:21:39.600 --> 00:21:41.990
highquality rotation is precisely the


00:21:42.000 --> 00:21:43.669
test that would confirm the patterns


00:21:43.679 --> 00:21:46.070
hold. So, we'll describe it as the test


00:21:46.080 --> 00:21:47.830
rather than the finding.


00:21:47.840 --> 00:21:50.390
>> And the second is our usual one.


00:21:50.400 --> 00:21:52.630
>> The preprint went up in late July, so


00:21:52.640 --> 00:21:54.549
there's about a 7-week gap before the


00:21:54.559 --> 00:21:56.310
journal version and the Trinity release


00:21:56.320 --> 00:21:58.789
this week. Shorter than yesterday's, but


00:21:58.799 --> 00:22:00.070
worth saying.


00:22:00.080 --> 00:22:03.669
>> And one lovely human detail to finish.


00:22:03.679 --> 00:22:06.070
SIMP0136


00:22:06.080 --> 00:22:09.270
is 20 light years away. The web data


00:22:09.280 --> 00:22:12.710
Shraider analyzed was gathered in 2023.


00:22:12.720 --> 00:22:14.710
So the light she was working with left


00:22:14.720 --> 00:22:17.590
that object in the year she was born.


00:22:17.600 --> 00:22:19.029
>> That's a very good reason to go into


00:22:19.039 --> 00:22:20.310
astronomy.


00:22:20.320 --> 00:22:22.950
>> Now we have one more quick one before


00:22:22.960 --> 00:22:24.230
Skywatch.


00:22:24.240 --> 00:22:26.870
>> We do indeed. The sun has gone very


00:22:26.880 --> 00:22:28.230
quiet indeed.


00:22:28.240 --> 00:22:29.510
>> How quiet?


00:22:29.520 --> 00:22:32.149
>> Very nearly blank. As of yesterday,


00:22:32.159 --> 00:22:34.149
there was exactly one numbered active


00:22:34.159 --> 00:22:36.549
region left on the Earth-facing side,


00:22:36.559 --> 00:22:38.630
AR4528,


00:22:38.640 --> 00:22:40.549
and it's rotating out of view as we


00:22:40.559 --> 00:22:43.669
speak. If nothing new emerges behind it,


00:22:43.679 --> 00:22:45.430
we're about to get the sun's first


00:22:45.440 --> 00:22:47.909
spotless day since the 24th of February


00:22:47.919 --> 00:22:49.029
this year.


00:22:49.039 --> 00:22:51.510
>> And February was itself notable.


00:22:51.520 --> 00:22:55.590
February ended a streak of 1,335


00:22:55.600 --> 00:22:57.510
consecutive days with at least one


00:22:57.520 --> 00:23:00.310
sunspot going all the way back to June


00:23:00.320 --> 00:23:01.990
2022.


00:23:02.000 --> 00:23:05.830
Solar cycle 25 peaked in October 2024.


00:23:05.840 --> 00:23:07.669
And this is what the downhill side looks


00:23:07.679 --> 00:23:11.110
like. For scale, the last solar minimum


00:23:11.120 --> 00:23:14.149
between 2018 and 2020 delivered


00:23:14.159 --> 00:23:17.029
something like 700 spotless days.


00:23:17.039 --> 00:23:19.510
>> And minimum itself is still some way


00:23:19.520 --> 00:23:23.270
off. not expected before about 2030. But


00:23:23.280 --> 00:23:25.430
here's the part worth holding on to, and


00:23:25.440 --> 00:23:27.110
it connects two stories we've run


00:23:27.120 --> 00:23:29.990
recently. A quiet sun is not a harmless


00:23:30.000 --> 00:23:32.870
sun. It's a differently hazardous one.


00:23:32.880 --> 00:23:35.350
We talked in episode 192 about the


00:23:35.360 --> 00:23:37.510
energy a big active region can store for


00:23:37.520 --> 00:23:40.630
a super flare. And in 193 about cosmic


00:23:40.640 --> 00:23:43.590
radiation at aviation altitudes. And


00:23:43.600 --> 00:23:45.909
that second one runs the opposite way.


00:23:45.919 --> 00:23:48.230
When the sun is quiet, its magnetic


00:23:48.240 --> 00:23:50.070
field does less to shield the inner


00:23:50.080 --> 00:23:52.870
solar system. So, galactic cosmic rays


00:23:52.880 --> 00:23:55.669
get through more easily. Radiation dose


00:23:55.679 --> 00:23:58.310
at cruising altitude runs 40 to 60%


00:23:58.320 --> 00:24:01.270
higher at solar minimum than at maximum.


00:24:01.280 --> 00:24:03.669
>> Same dial, opposite end.


00:24:03.679 --> 00:24:06.310
>> Fewer auroras, more cosmic rays.


00:24:06.320 --> 00:24:08.549
>> And that's a very good excuse to talk


00:24:08.559 --> 00:24:11.350
about the sky because tonight there is


00:24:11.360 --> 00:24:13.269
something genuinely worth walking


00:24:13.279 --> 00:24:15.510
outside for. and it works from


00:24:15.520 --> 00:24:17.029
everywhere.


00:24:17.039 --> 00:24:18.549
>> Venus.


00:24:18.559 --> 00:24:21.110
>> Venus at greatest brilliancancy.


00:24:21.120 --> 00:24:24.070
Tonight, the 18th of September, Venus


00:24:24.080 --> 00:24:25.990
reaches its peak brightness for this


00:24:26.000 --> 00:24:28.950
entire evening apparition, magnitude


00:24:28.960 --> 00:24:31.029
minus4.8.


00:24:31.039 --> 00:24:32.950
There is nothing else in the night sky


00:24:32.960 --> 00:24:35.269
that comes close except the moon.


00:24:35.279 --> 00:24:37.029
>> And the reason it peaks tonight rather


00:24:37.039 --> 00:24:39.590
than when Venus is full is genuinely


00:24:39.600 --> 00:24:41.110
counterintuitive.


00:24:41.120 --> 00:24:43.110
It's the best bit of physics in the


00:24:43.120 --> 00:24:45.830
whole segment. Venus is not full


00:24:45.840 --> 00:24:49.350
tonight. It's a crescent only about 26%


00:24:49.360 --> 00:24:52.230
lit. But because it's swinging in closer


00:24:52.240 --> 00:24:54.870
to us, that crescent has swollen to


00:24:54.880 --> 00:24:58.390
nearly 40 arcsec across. Brightness is


00:24:58.400 --> 00:25:00.710
lit fraction multiplied by apparent


00:25:00.720 --> 00:25:03.430
size. And right now the disc is growing


00:25:03.440 --> 00:25:05.750
faster than the illuminated fraction is


00:25:05.760 --> 00:25:06.789
shrinking.


00:25:06.799 --> 00:25:09.510
>> A big thin crescent beats a small full


00:25:09.520 --> 00:25:12.789
disc. every time. And if you have


00:25:12.799 --> 00:25:15.269
binoculars, hold them steady and you'll


00:25:15.279 --> 00:25:18.310
actually see the crescent shape. At 40


00:25:18.320 --> 00:25:21.029
arcsec, it's within reach, which


00:25:21.039 --> 00:25:22.950
surprises people because we don't think


00:25:22.960 --> 00:25:25.669
of Venus as something you can resolve.


00:25:25.679 --> 00:25:27.269
>> And if you see a different date quoted


00:25:27.279 --> 00:25:30.230
somewhere, some listings say the 22nd.


00:25:30.240 --> 00:25:32.950
Both are defensible. The peak is very


00:25:32.960 --> 00:25:35.990
flat. Between tonight and the 22nd, the


00:25:36.000 --> 00:25:40.390
lit fraction drops from about 26% to 23,


00:25:40.400 --> 00:25:42.390
while the disc grows from roughly 40


00:25:42.400 --> 00:25:46.470
arcsec to 42. And those two changes very


00:25:46.480 --> 00:25:48.470
nearly cancel. So, you're not going to


00:25:48.480 --> 00:25:50.870
miss it by going out on the wrong night.


00:25:50.880 --> 00:25:53.510
>> Now, how well you do tonight depends


00:25:53.520 --> 00:25:55.909
enormously on where you're standing, and


00:25:55.919 --> 00:25:58.070
the gap is dramatic.


00:25:58.080 --> 00:26:00.710
>> From Sydney, this is a spectacle. Sunset


00:26:00.720 --> 00:26:03.830
is at4 to 6 and at that moment Venus is


00:26:03.840 --> 00:26:06.950
39° above the western horizon. That's


00:26:06.960 --> 00:26:09.430
more than a third of the way up the sky.


00:26:09.440 --> 00:26:11.830
It doesn't set until just before 9:00,


00:26:11.840 --> 00:26:14.070
which gives you 3 hours and 13 minutes


00:26:14.080 --> 00:26:17.190
of Venus after sunset. You do not need a


00:26:17.200 --> 00:26:20.149
clear horizon. You do not need to hurry.


00:26:20.159 --> 00:26:22.549
>> And from the northern hemisphere, it's a


00:26:22.559 --> 00:26:25.269
different evening entirely. From Los


00:26:25.279 --> 00:26:28.950
Angeles, sunset is at 10 to 7 and Venus


00:26:28.960 --> 00:26:32.789
is 14° up. It sets an hour and 19


00:26:32.799 --> 00:26:35.590
minutes after the sun. From New York,


00:26:35.600 --> 00:26:39.350
10° up, 1 hour and 3 minutes. From


00:26:39.360 --> 00:26:43.590
London, 3 1/2° at sunset and gone 28


00:26:43.600 --> 00:26:44.789
minutes later,


00:26:44.799 --> 00:26:47.190
>> which is not Venus being fainter. It's


00:26:47.200 --> 00:26:49.269
exactly as bright everywhere. It's the


00:26:49.279 --> 00:26:50.470
geometry.


00:26:50.480 --> 00:26:53.350
>> It's the tilt of the ecliptic. At this


00:26:53.360 --> 00:26:55.110
time of year, the plane of the solar


00:26:55.120 --> 00:26:57.510
system stands almost vertically out of


00:26:57.520 --> 00:26:59.590
the western horizon at dusk from the


00:26:59.600 --> 00:27:02.149
southern hemisphere. So anything on that


00:27:02.159 --> 00:27:04.549
plane climbs steeply and takes a long


00:27:04.559 --> 00:27:06.710
time to set. From the northern


00:27:06.720 --> 00:27:09.510
hemisphere in September, that same plane


00:27:09.520 --> 00:27:11.750
lies down almost flat against the


00:27:11.760 --> 00:27:14.310
horizon and everything on it skims


00:27:14.320 --> 00:27:16.149
sideways and sets quickly.


00:27:16.159 --> 00:27:18.310
>> So northern listeners, here's the


00:27:18.320 --> 00:27:20.710
practical version. Find a spot with a


00:27:20.720 --> 00:27:24.070
genuinely clear, flat western horizon.


00:27:24.080 --> 00:27:27.190
No trees, no buildings. Start looking 20


00:27:27.200 --> 00:27:29.110
minutes after sunset and don't leave it


00:27:29.120 --> 00:27:31.590
much past 45. It'll be the brightest


00:27:31.600 --> 00:27:33.190
thing in that part of the sky by an


00:27:33.200 --> 00:27:35.350
enormous margin, so you won't be in any


00:27:35.360 --> 00:27:36.789
doubt once you've got it.


00:27:36.799 --> 00:27:39.750
>> And a bonus for the south, Mercury is up


00:27:39.760 --> 00:27:43.190
there, too. From Sydney, Mercury is 16


00:27:43.200 --> 00:27:46.070
degrees above the horizon at sunset and


00:27:46.080 --> 00:27:48.789
doesn't set for an hour and 20 minutes,


00:27:48.799 --> 00:27:50.789
which for Mercury is a comfortable


00:27:50.799 --> 00:27:53.510
viewing window. From Los Angeles, it's


00:27:53.520 --> 00:27:58.549
9° and 43 minutes. From London, 4° and


00:27:58.559 --> 00:28:01.350
26 minutes. That one really is a


00:28:01.360 --> 00:28:03.190
southern target this week.


00:28:03.200 --> 00:28:05.029
>> And then there's the moon, which is


00:28:05.039 --> 00:28:07.350
doing something rather precise tonight.


00:28:07.360 --> 00:28:10.230
>> First quarter, and it's exact. The moon


00:28:10.240 --> 00:28:13.669
reaches first quarter at 20:43 universal


00:28:13.679 --> 00:28:16.310
time tonight. That's quarter to 5 on


00:28:16.320 --> 00:28:19.510
Friday afternoon in New York,4 to 2 in


00:28:19.520 --> 00:28:22.789
Los Angeles to 10 on Friday evening in


00:28:22.799 --> 00:28:26.389
London. And for Australia, 20 to 7 on


00:28:26.399 --> 00:28:27.669
Saturday morning.


00:28:27.679 --> 00:28:29.669
>> And from Sydney tonight, the moon is


00:28:29.679 --> 00:28:32.789
very nearly overhead. 82 degrees up at


00:28:32.799 --> 00:28:34.310
sunset, which is close enough to


00:28:34.320 --> 00:28:35.669
straight up that you'll find yourself


00:28:35.679 --> 00:28:37.590
leaning back to look at it. which


00:28:37.600 --> 00:28:40.070
matters because tomorrow night, Saturday


00:28:40.080 --> 00:28:42.950
the 19th, is international observe the


00:28:42.960 --> 00:28:44.070
moon night.


00:28:44.080 --> 00:28:45.830
>> And the timing of that is not an


00:28:45.840 --> 00:28:47.909
accident. It's deliberately scheduled


00:28:47.919 --> 00:28:50.230
near first quarter because first quarter


00:28:50.240 --> 00:28:51.990
is when the moon is at its most


00:28:52.000 --> 00:28:54.630
interesting through any optical aid.


00:28:54.640 --> 00:28:57.029
Along the terminator, the line dividing


00:28:57.039 --> 00:28:59.350
day from night, the sun is striking the


00:28:59.360 --> 00:29:01.669
surface at a grazing angle. So every


00:29:01.679 --> 00:29:03.750
crater rim and mountain throws a long


00:29:03.760 --> 00:29:06.149
shadow across the ground behind it. A


00:29:06.159 --> 00:29:09.190
full moon looks flat. A half moon looks


00:29:09.200 --> 00:29:10.630
three-dimensional.


00:29:10.640 --> 00:29:12.950
>> Completely three-dimensional. Run the


00:29:12.960 --> 00:29:14.630
terminator with even a small pair of


00:29:14.640 --> 00:29:16.789
binoculars and the whole landscape


00:29:16.799 --> 00:29:19.350
stands up out of the surface. If you've


00:29:19.360 --> 00:29:20.870
only ever looked at a full moon and


00:29:20.880 --> 00:29:22.870
found it disappointing, this is the


00:29:22.880 --> 00:29:25.669
night to try again. NASA's own event is


00:29:25.679 --> 00:29:27.590
at the US Space and Rocket Center in


00:29:27.600 --> 00:29:29.750
Huntsville, Alabama. But the whole point


00:29:29.760 --> 00:29:32.070
is that it's global. You just need to go


00:29:32.080 --> 00:29:33.190
outside.


00:29:33.200 --> 00:29:35.350
>> And to balance the ledger because the


00:29:35.360 --> 00:29:37.510
south has had the better of the evening.


00:29:37.520 --> 00:29:39.990
The morning sky belongs decisively to


00:29:40.000 --> 00:29:40.950
the north.


00:29:40.960 --> 00:29:43.510
>> It does. Mars and Jupiter are both


00:29:43.520 --> 00:29:45.830
climbing in the pre-dawn east. And the


00:29:45.840 --> 00:29:47.750
same ecliptic geometry that flattened


00:29:47.760 --> 00:29:50.070
Venus for northern viewers works the


00:29:50.080 --> 00:29:52.310
other way around before sunrise. At


00:29:52.320 --> 00:29:54.950
nautical dawn tomorrow morning, Mars is


00:29:54.960 --> 00:29:58.230
48° up from Los Angeles and 46 from New


00:29:58.240 --> 00:30:01.909
York and 41 from London. Avery and from


00:30:01.919 --> 00:30:02.870
Sydney,


00:30:02.880 --> 00:30:05.830
>> 20°. So that's very much your sky, not


00:30:05.840 --> 00:30:09.510
ours. Jupiter is 26° up from Los Angeles


00:30:09.520 --> 00:30:10.950
and 9 from Sydney.


00:30:10.960 --> 00:30:13.590
>> And those two are closing on each other.


00:30:13.600 --> 00:30:16.789
They're about 23° apart this morning. By


00:30:16.799 --> 00:30:20.149
midocctober, that's down to 12. And by


00:30:20.159 --> 00:30:22.389
the middle of November, they'll be a


00:30:22.399 --> 00:30:24.870
little over a degree apart. Close enough


00:30:24.880 --> 00:30:26.870
to cover with a fingertip at arms


00:30:26.880 --> 00:30:31.029
length. That's the one to diarize.


00:30:31.039 --> 00:30:33.269
Saturn, meanwhile, is up essentially all


00:30:33.279 --> 00:30:35.430
night from everywhere. It doesn't set


00:30:35.440 --> 00:30:37.190
until nearly 7 in the morning from


00:30:37.200 --> 00:30:39.510
Sydney and just before 8 from Los


00:30:39.520 --> 00:30:41.669
Angeles. and it's building toward


00:30:41.679 --> 00:30:44.149
opposition on the 4th of October when


00:30:44.159 --> 00:30:46.310
the disc will be about 19 and a half


00:30:46.320 --> 00:30:49.750
arcsec across with the rings roughly 7°


00:30:49.760 --> 00:30:51.430
open


00:30:51.440 --> 00:30:53.990
>> and the equinox next week


00:30:54.000 --> 00:30:55.750
>> which we'll flag carefully because we


00:30:55.760 --> 00:30:57.590
got this slightly wrong in an earlier


00:30:57.600 --> 00:31:00.230
episode and corrected it. The September


00:31:00.240 --> 00:31:03.510
equinox is a single instant, not a day.


00:31:03.520 --> 00:31:05.669
5 minutes past midnight universal time


00:31:05.679 --> 00:31:08.230
on the 23rd. That's the evening of the


00:31:08.240 --> 00:31:10.870
22nd across the Americas and midm


00:31:10.880 --> 00:31:13.350
morning on the 23rd in Australia. So,


00:31:13.360 --> 00:31:15.190
the date depends entirely on where


00:31:15.200 --> 00:31:16.549
you're standing.


00:31:16.559 --> 00:31:18.470
>> And one last thing which follows


00:31:18.480 --> 00:31:20.389
directly from that quick hit about the


00:31:20.399 --> 00:31:23.110
blank sun because every time we mention


00:31:23.120 --> 00:31:25.830
sunspots, people quite reasonably want


00:31:25.840 --> 00:31:27.669
to go and look.


00:31:27.679 --> 00:31:30.310
>> And you can, but never ever with


00:31:30.320 --> 00:31:32.549
unprotected eyes and never through


00:31:32.559 --> 00:31:34.630
binoculars or a telescope that isn't


00:31:34.640 --> 00:31:37.110
purpose-built for it. The only safe way


00:31:37.120 --> 00:31:39.430
to look directly at the sun is through


00:31:39.440 --> 00:31:41.509
filters certified to the international


00:31:41.519 --> 00:31:45.669
standard ISO12312-2.


00:31:45.679 --> 00:31:48.310
That's eclipse glasses or a proper solar


00:31:48.320 --> 00:31:49.830
filter fitted over the front of the


00:31:49.840 --> 00:31:53.110
instrument. Never on the eyepiece end.


00:31:53.120 --> 00:31:55.750
>> And ordinary sunglasses are not solar


00:31:55.760 --> 00:31:58.470
filters. Neither is smoked glass,


00:31:58.480 --> 00:32:01.750
exposed film, a CD, or stacking several


00:32:01.760 --> 00:32:04.149
pairs of sunglasses together.


00:32:04.159 --> 00:32:06.070
>> None of those are safe. Check your


00:32:06.080 --> 00:32:09.909
eclipse glasses for the ISO12312-2


00:32:09.919 --> 00:32:11.830
marking. And if they're scratched,


00:32:11.840 --> 00:32:13.190
punctured, or you can't find the


00:32:13.200 --> 00:32:15.830
marking, don't use them. The safest


00:32:15.840 --> 00:32:18.070
option of all, and honestly the best one


00:32:18.080 --> 00:32:21.110
for a group, is projection. Put the


00:32:21.120 --> 00:32:23.029
sun's image onto a white card and


00:32:23.039 --> 00:32:24.549
everybody can look at once without


00:32:24.559 --> 00:32:26.389
anyone looking up.


00:32:26.399 --> 00:32:28.470
>> Although this week there may be nothing


00:32:28.480 --> 00:32:31.190
to see, which is rather the point.


00:32:31.200 --> 00:32:33.110
>> That's Astronomy Daily for Friday the


00:32:33.120 --> 00:32:35.350
18th of September. Everything we've


00:32:35.360 --> 00:32:37.190
talked about today, the papers, the


00:32:37.200 --> 00:32:39.750
DOIs, the full skywatch figures for all


00:32:39.760 --> 00:32:42.710
four cities is in the show notes and on


00:32:42.720 --> 00:32:45.990
the website at astronomyaily.io


00:32:46.000 --> 00:32:47.990
>> where you'll also find the full back


00:32:48.000 --> 00:32:50.789
catalog, the daily newsletter, and the


00:32:50.799 --> 00:32:53.509
contact form. And do use that contact


00:32:53.519 --> 00:32:55.909
form. Some of our favorite segments this


00:32:55.919 --> 00:32:58.070
year have come from listener questions,


00:32:58.080 --> 00:33:00.549
and we read every one of them.


00:33:00.559 --> 00:33:03.190
>> Go out tonight and look west. Venus will


00:33:03.200 --> 00:33:05.590
not be this bright again this year.


00:33:05.600 --> 00:33:08.389
>> And tomorrow night, look at the moon.


00:33:08.399 --> 00:33:09.909
>> We'll be back on the weekend with this


00:33:09.919 --> 00:33:12.389
week's weekend rap. Until then, clear


00:33:12.399 --> 00:33:24.389
skies.


00:33:24.399 --> 00:33:28.200
Stories told.