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Full Transcript below

Dr Ian ‘Astroblog’ Musgrave returns with your essential guide to the October night sky, including Saturn at opposition on the 4th, Mars crossing the Beehive Cluster (M44), the Orionid meteor shower, and a daylight Lunar X on the 18th. Daylight saving begins on October 4 for the states that observe it.

Venus is sinking into the twilight as a wire-thin crescent on its way to inferior conjunction on the 24th, while Mercury climbs to greatest elongation (25°) and joins it, with a slim crescent Moon between the two on the 12th. Jupiter and Mars share the pre-dawn sky, T Coronae Borealis still hasn’t gone bang, and the Moon occults Elnath (Beta Tauri) around midnight on October 29–30.

In the Tangent, Ian explores the long-standing mystery of the “unknown absorber” in Venus’s clouds. A new candidate molecule, the controversial phosphine detection, and extremophiles in Earth’s black smokers raise a tantalising question: could life be drifting in Venus’s upper atmosphere?

In This Episode:

• Moon Phases: Last Quarter (Oct 3), New Moon (Oct 11), First Quarter (Oct 19), Full Moon (Oct 26), plus perigee and apogee dates
• Daylight Lunar X: Oct 18, with viewing times for the eastern, central and western states
• Evening Skies: Mercury at greatest elongation, a Mercury–Venus–crescent Moon grouping on the 12th, Mercury near Alpha Librae on the 13th, and Venus becoming a wire-thin crescent before inferior conjunction on the 24th
• Saturn at Opposition (Oct 4): the best telescope viewing time, wide rings, ring spokes, and the Moon guiding you to Saturn on the 24th
• Morning Skies: the crescent Moon passing Mars and Jupiter (Oct 5–7), Mars in the heart of the Beehive Cluster on the 12th, and Jupiter in Leo
• T Coronae Borealis: still waiting, and why Australian observers may miss the outburst
• The Occultation of Elnath (Beta Tauri), Oct 29–30: best from the east coast, with Canberra and Sydney seeing it vanish and reappear
• The Orionid Meteor Shower: when to look, how the Moon will interfere, and why the window around 4–5 a.m. matters
• Deep-Sky Spotlight: Scorpius, Sagittarius and the teapot, M22, the Andromeda Galaxy, the Small Magellanic Cloud, 47 Tucanae and the Southern Cross
• The Tangent: Venus’s “unknown absorber”, organic compounds and peptides in sulfuric acid clouds, the phosphine debate, and Earth’s black-smoker microbes as a model for life above Venus
  
• October Highlights:
  
• Evening Sky:

04 October: Saturn Opposition (closest to Earth)
05 October: Moon near Mars: 1.2° in the morning
06 October: Moon close to Jupiter in the morning
07 October: Mercury near Venus: 5° in the evening twilight.
12 October: Mars in the heart of the Beehive cluster
12 October: Moon near Venus 3.3°in the evening twilight with Mercury above
13 October: Moon near Mercury 2.3°in the evening twilight with Venus below. Asteroid 4 Vesta at opposition (Magnitude 6.5, binoculars or telescope)
21-22 October: Orionid meteor shower
28 October: Moon very close to the Pleiades <1°

Full Transcript: Introduction

Welcome to episode 243 of Astrophiz. My name is Brendan O’Brien and Astrophiz is produced on Yorta Yorta, Pangarang and Kaurna country. We celebrate the first astronomers of this land.

Twice monthly, we explore the universe with the world’s leading scientists. For transcripts and more, visit Astrophiz.com.

And here is Dr. Ian Musgrave with your October SkyGuide.

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Brendan: Hello, Ian.

Ian: Hello, Brendan.

Brendan: Great to be speaking with you again, Ian. And can you tell us, what can we look out for in the celestial sky for October?

Ian: Well, the celestial spheres are going to show us lots of interesting action. Now, the planetary action is being split between the evening and morning skies.

Venus, our evening star, is beginning to sink in the early twilight and will be lost to view around mid-month. Mercury is prominent in the early evening sky until mid-month, but it’s close to Venus. It will take a little bit longer to disappear than Venus will, so we’ll have something good to look at.

Saturn, of course, is at opposition, when it’s biggest and brightest as seen from Earth, this month. It’s visible all night, so both the evening and morning sky will feature the ringed world. Jupiter’s in the morning sky, below Mars. We’ve also got the Orionid meteor shower and an occultation of Beta Tauri.

Now, let’s go into a bit more detail. In terms of Earth, daylight saving time begins for all those states that observe it on the 4th of October. So you’ll see changes in dates as I talk about things.

The October Moon Phases

Ian: Let’s go to the Moon first, our guide to the heavenly spheres. October 3 is Last Quarter, which is ideal for stargazing in the evening. October 11 is New Moon, which is ideal for stargazing at all times of the night. October 19 is First Quarter. Now, there’s a daylight Lunar X on the 18th, the day before. October 26 is Full Moon.

Now, the Moon is at perigee, when it’s closest to Earth, on October 2, and again on October the 29th, but this time there’s also the occultation of Beta Tauri, which is quite low to the horizon. The Moon is at apogee, when it’s furthest from the Earth, on October the 17th.

Okay, and just for the detail of the Lunar X: the Lunar X is visible at about half past four in the evening in the eastern states, about four o’clock in the central states, and about 1:30 in Western Australia. Now, of course, this means the Moon’s in daylight, which may make it very difficult to see, but it will still be visible in the twilight from everywhere. You may wish to try to observe it when the Sun’s quite low in the sky, keeping safe solar observing in mind, just so you don’t accidentally see the Sun as you’re looking at the Moon.

Evening Skies: Mercury, Venus and Saturn

Ian: Okay, evening sky. Mercury has joined us in the evening sky, and it’s high in the western evening twilight for the first half of the month. On the 6th and 7th, it’ll be 5 degrees from far brighter Venus, so the two will be quite close together.

Mercury reaches its greatest elongation, its distance from the Sun, of 25 degrees on the 12th. Also on the 12th, the two-day-old thin crescent Moon will appear about 5 degrees away, between Mercury and Venus, and that will make quite a nice sight. It’s best seen around about an hour after the Sun has set, in nautical twilight.

On the 13th, Mercury is about three degrees to the right of the third-magnitude star Alpha Librae. And Alpha Librae is a beautiful binary of brilliant white stars. It’s well worth looking at in binoculars, so Mercury and Alpha Librae will be within the same binocular field. However, by the month’s end, Mercury is deep in the twilight.

Now, Venus, which has been our brilliant companion for many months, is descending towards the horizon and will be at inferior conjunction, when it’s between the Sun and Earth, on the 24th. While we’ve got it for the first couple of weeks, Venus is becoming larger and thinner. I’ve said before it’s an obvious crescent phase, but it’s really starting to become this wire-thin crescent. And the crescent phase is visible in 10 by 50 binoculars. I had a look earlier this week when I was imaging Venus, and you can indeed see the crescent phase at the moment with binoculars, and it’ll only become more pronounced as it heads towards inferior conjunction.

Brendan: Nice.

Ian: Now, as I said, on the 12th, Venus will be three degrees to the left of the two-day-old crescent Moon, with Mercury above. At this distance, Venus and the Moon will be in the same binocular field. They’re too far apart for telescopes from Australia, so it won’t be a good telescopic sight. In 10 by 50 binoculars you’ll be able to see the thin crescent Venus and the thin crescent Moon side by side in the early twilight.

You may need to put your binoculars on a tripod or something solid, to stop your hands shaking, so that you can see Venus at its best. It’s also a good idea to do it in the early twilight, because as the twilight deepens, the brightness of Venus can cause reflection artifacts in your binoculars, making it hard to see the crescent shape.

As well as Venus becoming an amazingly thin crescent, we have Saturn coming to opposition. Now, Saturn is, of course, at its biggest and brightest this season from Earth on the 4th, and it’s going to be visible the entire night. Even though opposition is on the 4th, because of its distance, Saturn will be quite big and bright for some time before and after the 4th. So if you can’t get to it on the 4th, don’t worry, you’ll have plenty of time to see it quite nicely.

Telescopically, it’s best viewed around about midnight, when it’s at its highest. Unfortunately, we’ve been having a very warm autumn, and you might expect your observing to be disturbed by atmospheric turbulence. But if you’re observing around midnight, when Saturn is high and the sky is much cooler, you’ll have a lot better view.

Now, the rings are wide, and if you caught Saturn last year when the rings were nearly edge-on, they’re looking quite good at the moment. But if you’ve got a big telescope, you might want to watch out for the spokes of the rings. Saturn’s rings are impacted by various meteoroids, and these generate patches of dust which can be seen rotating along the ring. There was a big hit recently with a very large discoloration which would be rotating along the rings. So keep your eye out and you might see something quite spectacular. For those of us with tiny telescopes, the rings are still pretty amazing.

And on October the 24th, the waxing Moon is about seven degrees from Saturn, a little bit over a hand span. So if by that time you are still not sure which one of the brightest objects above the eastern horizon at the moment is Saturn, then the Moon will be your guide.

Morning Skies: Saturn, Mars and Jupiter

Ian: Okay, let’s flip to the morning sky. Saturn will be seen in the west. And again, if you want to view it, the best viewing time is around about midnight to early morning.

Mars is rising about 2 a.m. in Cancer. And on the 5th, it’s 7 degrees, just a bit over a hand span, from the 23-day-old waning crescent Moon. And from the 11th to the 13th, Mars crosses the Beehive Cluster, M44, in Cancer. Now, at magnitude 1, the red planet is much brighter than any of the stars of the Beehive Cluster, and this will make it an interesting photo opportunity. In this particular case, on the 12th, it’s dead in the heart of the Beehive Cluster. In previous years, it’s gone a bit up or a bit below the Beehive, but this year it’s going to be dead in the middle. So I would strongly recommend that anyone getting up at ungodly hours see if you can catch Mars in the Beehive Cluster.

Brendan: Cool.

Ian: Then Jupiter is also rising around about 2:30 a.m., but that’s mid-month. It’s still quite low. It’s visible in the eastern morning sky in Leo, and on the 7th, the planet is 5 degrees from the 26-day-old waning crescent Moon.

So if you’re up early in the morning from the 5th to the 7th, you’ll see the crescent Moon coming first close to Mars, then between Mars and Jupiter, then close to Jupiter. And on the 7th, the crescent Moon, Regulus and Jupiter form a nice line in the sky.

Brendan: Yep.

T Coronae Borealis

Ian: Now, you’re probably wanting to know what’s happened to T Coronae Borealis.

Brendan: Yep.

Ian: No, it hasn’t gone bang. I keep getting little notifications and a breathless astronomer saying, “Oh, it’s 2026, it should be time for it to go bang.” It still hasn’t. Now, from Australia, it’s sitting around nautical twilight and we’re unlikely to see it until next month, when it’ll be visible in the early morning. So if it goes bang now, it’s going to be too late for us to see it.

Brendan: Yeah.

The Occultation of Beta Tauri (Elnath), October 29–30

Ian: So, onto the occultation of Beta Tauri. This is on Thursday, October 29, around about midnight, so it crosses the 29th and 30th boundary. It’s mostly seen best on the east coast. The Moon is waning and it’s going to be very low above the horizon. For most places, the Moon rises with Elnath occulted. So again, if you’re looking at around about midnight, if you see the Moon rising and then the star will pop out from behind the dark limb of the Moon. I’ll give proper times for all the sites later on.

Actually, Canberra does slightly better. It gets to see Elnath go behind the Moon and come out, as does Sydney. Perth and Darwin miss out totally.

The Orionid Meteor Shower

Ian: Now, on to the meteor shower. The Orionids are normally a worthwhile shower, best seen between 2 and 4 a.m., and the radiant is just under Betelgeuse, the bright red star in Orion.

Now, this year, the waning Moon will significantly interfere with viewing in the early morning, and the rates will be low, but once the Moon sets around 4 a.m., the rates will be better. The best viewing is on the mornings of the 21st to 23rd, with the highest rates on the morning of the 23rd, so between 4 and 5 a.m.

Now, that’s a very narrow window. We’ve got the Moon setting around about 4 a.m. The radiant isn’t quite at its highest until around 5 a.m., but shortly after 5 a.m. you’ve got the end of astronomical twilight and nautical twilight coming up, so the rates will go down. But under dark skies, usually you’ll see a meteor about every four minutes or so. So if you’re prone to getting up early in the morning, it’s well worthwhile getting up and having a look for the Orionids. And of course, Betelgeuse and Orion are really good markers to where the meteor shower is.

Brendan: Worth setting your alarm for.

Ian: Very definitely worth setting an alarm for.

Deep Sky: Scorpius, Sagittarius, Andromeda and the Southern Cross

Ian: Now, with the stars, Scorpius forms a reversed question mark above the western horizon, and if you watch during the night you’ll see the head disappear below the horizon, leaving the curled tail just above.

Sagittarius and the centre of the galaxy have passed the zenith, but still remain excellent binocular hunting ground, as I said last podcast. The lid of the teapot of Sagittarius is the great globular cluster M22. It’s well worth bringing binoculars, and nearby are the Trifid and Lagoon Nebulae.

Now, I mentioned the famous Andromeda Galaxy last podcast, and around midnight it’s coming up to its highest in the north. Of course, in Australia it’s still low, but it should be easily visible in binoculars, especially as the Moon is leaving the sky. Even under suburban conditions, we should be able to pick it up quite nicely in binoculars.

But at the same time, one of our companion galaxies, the Small Magellanic Cloud, and the magnificent globular cluster 47 Tucanae are quite high, and they’re almost due south.

And then around 10 p.m. local time, the Southern Cross will be almost at the five o’clock position of the sky, and by midnight it will be almost at six o’clock. So there’s plenty to see in the southern skies this time round. Lots of planets, lots of stars, meteor showers, occultations, and who knows what else. October, Rocktober.

Brendan: Ian, do you have a tangent for us for October?

Ian: I do have a tangent for us.

The Tangent: Venus’s Unknown Absorber, Phosphine, and Life in the Clouds

Ian: Now, if you’ve been watching Venus, you’ve seen it as a featureless blob in your binoculars. But this month, Venus swells in size and becomes, as I said before, a wire-thin crescent. And even in binoculars, you’ll be able to see its crescent shape. But seen through binoculars and telescopes, Venus is plain, almost blindingly white and featureless, or maybe a yellowish colour. Its surface is eternally cloaked in clouds.

But if you put a swingeingly expensive UV filter on your telescope, you can see structures in the clouds: dramatic dark and bright patterns that move with the planet’s upper sulfuric acid clouds. Now, astronomers have known about these bands for roughly a century. And yet the chemical identity of the material responsible, the unknown absorber making these bands, remains a mystery.

So a group of researchers have modelled the nature of the cloud droplets and the absorption characteristics of the unknown absorber, and looked at the kinds of materials that would produce these dark absorption bands. And after eliminating a lot of ordinary chemicals that might be in the sulfuric acid clouds, they concluded that the likely candidate was an organic compound.

Now, don’t get too excited. An organic compound is anything that’s simply made of chains of carbon atoms. And in the words of one of the researchers: “If the observed light absorption is due to conjugated organic matter, the relatively sharp absorption profile is consistent with a chemically defined absorber that resists conversion into the tarry mixtures we usually observe with organics dissolved in concentrated sulfuric acid.” And if any of you have ever done organic chemistry, at high school or uni, that is exactly what that feels like.

Brendan: Nice.

Ian: So what could this mysterious compound or compounds be? Well, hot on the heels of this announcement comes the finding that peptides might exist in the Venusian clouds. Now, peptides are basically the building blocks of proteins, and they’re not the peptides that people are currently injecting. But the peptides, short chains of amino acids, adopt stable [unclear] structures in concentrated sulfuric acid. And hydrolysis is limited in the nearly water-free acidic solution, like those in the clouds of Venus. So we have a potential candidate for the mysterious absorber.

But you say, where do these peptides come from? Now, do you remember phosphine? Back in 2020, it was allegedly detected in the atmosphere of Venus. This was an extremely controversial claim. The infrared telescope on the back of the 747, SOFIA, failed to confirm the phosphine. But other observations and legacy data from the Pioneer spacecraft all confirmed that phosphine is there. And interestingly, its absorption characteristics suggest that it’s been broken down at the day–night terminator, which suggests that it’s being generated continuously.

Now, why is phosphine important? Because phosphine is seen as a biosignature. It’s produced by living organisms. It’s very hard to find a non-organic way to produce phosphine, and certainly to have phosphine coming up from the clouds. So could it be due to organisms?

Now, just listen to me say that Venus is covered in clouds of sulfuric acid, which are notably hostile to organisms. The bottoms of the clouds are at insane pressures and temperatures, hot enough to melt lead. But high in the clouds, the temperatures are more clement, just merely being hot, and the pressures are more like one atmosphere. Still hot to warmish, still lots of sulfuric acid. What sort of organisms would live in these sorts of conditions?

Well, if anyone has been looking at the underwater black smokers, we’ve got all sorts of microbes that are living in near-boiling water at great depths that contains a lot of acid in it. If Earth bacteria can survive under these conditions, perhaps bacteria could be living in the clouds of Venus. And it’s been suggested that the upper atmosphere is sufficiently stable that organisms could live in the upper reaches of the atmosphere, and that the circulation would not necessarily pull them down into the stultifying depths where no organism, not even a hot black-smoker organism, can survive.

So things are looking interesting at the moment. Of course, all of this has to be confirmed. Missions to Venus have been suggested to confirm the phosphine observation, and studies of the phosphine dynamics are being suggested. More detailed observations and experiments are needed to work out if the unknown absorber really is a peptide, and if these peptides are coming from living organisms. All these experiments have to be done.

But on the face of it, there are a number of interesting observations which are coming together to suggest that life in the clouds of Venus may not be as fanciful as we once thought. Venus may not be the hot, humid, tropical world that early science fiction writers imagined. But life may still persist. Not rainforests, but organisms that may be at home in the black-smoker depths of the pressurised oceans of Earth.

Brendan: Wow. So the possibility of life on or above Venus. Not friendly life, quite hostile life, but life nonetheless, a possibility.

Ian: Yeah, and if it pans out, this would be truly amazing. Of course, we don’t know if life evolved on Venus or if life came to Venus from material ejected from Earth during meteor impact. But it is interesting.

At the same time, the Mars rover has discovered inclusions in rocks which look like inclusions that are produced by living organisms back on Earth. Again, it could be some weird chemistry. We had a similar thing happen with the observations of the Kuiper Belt objects, where the colours and absorbance levels of the organics that we saw on the Kuiper Belt objects looked like the spectral signatures of amino acids. But it turned out that these were, in fact, Titan tholins, weird tarry-like stuff that was produced by ultraviolet action on methane.

So we’ve had a range of false signals before, or rather signals that got everyone’s hopes up, and then we looked at it and found really interesting chemistry, but it wasn’t life. So is it going to be really interesting chemistry? Is it going to be life?

And this is important because, for example, phosphine has been thought of as a potential biosignature for exoplanets. And if phosphine is really being produced by life in the Venus clouds, then this makes a strong case for looking for biosignatures using phosphine on our exoplanets.

Brendan: Another great example of science never sleeping, Ian.

Ian: Indeed.

Brendan: Excellent. Ian, well, thank you very much, Ian ‘Astroblog’ Musgrave, for giving us this beautiful window into October. Get out there and look up, everyone. Good night, Ian.

Ian: Good night, Brendan.

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And in two weeks’ time, I’m zooming right across the Tasman Sea to Auckland in New Zealand to speak with Laura Burn, a fantastic PhD candidate whose work sits right at the frontier of gravitational wave astronomy. She models the gravitational waves thrown off by merging supermassive black holes. And we’ll also hear about the upcoming LISA mission, humanity’s first gravitational wave observatory in space. You’ll love her. Tune in.

And remember, Astrophiz is free, ad-free, and unsponsored. Find us on Astrophiz.com or your favourite social media platform. Keep looking up. Clear skies.

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