The Supermassive Podcast - 53: The Major Lunar Standstill

Episode Date: June 4, 2024

Every 18.6 years, our moon reaches its farthest northern and southern point, known as a major lunar standstill. This month, Izzie and Dr Becky are exploring why this might be significant to Stonehenge in the UK and another historical site in the US called Chimney Rock. With special thanks to Dr Heather Sebire, Dr Amanda Chadburn and Dr Erica Ellingson. The southernmost Moonrise at Stonehenge will be livestreamed, allowing viewers to witness this celestial spectacle firsthand. Plus, there'll be events throughout the standstill season which include talks, a pop-up planetarium, stargazing sessions, storytelling, and a new exhibition display at the Stonehenge visitor centre in October. To find out more, visit...   https://www.english-heritage.org.uk/visit/places/stonehenge/things-to-do/major-lunar-standstill/#:~:text=Stonehenge%20is%20famous%20for%20its,'major%20lunar%20standstill'%20occurs. Or have a look at Chimney Rock in Colorado:  https://www.chimneyrockco.org/puebloan-resources/lunar-standstill/ The Supermassive Podcast is a Boffin Media Production. The producers are Izzie Clarke and Richard Hollingham. 

Oh wow, the moon is actually unusually high in the sky or unusually low. The moon's orbit isn't a perfect circle, it's oval shape. Can we just talk about phases of the moon? Hello and welcome to the Supermassive podcast from the Royal Astronomical Society with me, science journalist Izzy Clark and astrophysicist Dr Becky Smedder. This month we're becoming archaeo astronomers as we explore a special event called the Lunar Standstill. What is it? What does it have to do with significant cultural and historical sites around the world? Yeah so we'll get on to that

very shortly because we'll be joined by the Senior Property Curator of Stonehenge for English Heritage Heather Sabir as well as. Erica Ellingson, Astroarchaeologist from University of Colorado at the historical site in the US, Chimney Rock. Astroarchaeologist is just a really cool job title, isn't it? Like, I kind of feel like they give us a run for our money as an astrophysicist. I know, I know. To be honest, I have been speaking to many astroarchaeologists and archaeoastronomers

and it just makes you think like, oh my gosh, you've combined two fields that both blow my mind. You somehow merged like space and dinosaurs in my head. Basically, yeah. Not quite, but yeah, almost. And as ever, we have the expertise

of Dr. Robert Massey, the Deputy Director of the Royal Astronomical Society. Let's get into this immediately. What is the lunar standstill? Well, the lunar standstill happens every 18.6 years, the major lunar standstill. And what it means is that the Moon's orbit is lined up in such a way that it reaches its maximum north and south points in the sky as seen from earth and what that means is that it goes to quite extreme rising and setting points on the horizon too so at one point in the month you might have moon maxing out its time above the horizon really high up in the sky and then two weeks later it's minimizing its time in the sky

and it's really low down and actually both of those can be spectacular because if you ever think about the view with the moon illusion of a moon low on the horizon that looks bigger than it really is, that's a really nice thing to see as well. I should do a minor plug for a book I wrote about five years, including this, which I think is out of print, but get it on eBay. It's Moon Art Science Culture. Have a look at that. We talk about those things in there too. It's moon art science culture. Have a look in there. We talk about those things in there too. Going into the specifics of this,

can you talk about what you might expect it to look like in that sky? The appearance in the sky, look, it will still look like the moon. But if you imagine when it's at its furthest north in the sky, so, you know, things are higher and lower in the sky. If you're in the UK, we're in the northern part of the sky. So generally as things move further north, right up to the zenith point the overhead point they they're getting higher um and when they're further south they're lower in the sky during the major lunar standstill

the moon is at its highest can be at its highest possible point and what that means then as well is if it is very high against the star background that it will also set a rise in the extreme northeast and set in the extreme northwest and you know that that's a really nice thing to see you know it means the moon's above the horizon for a long time uh you know just a just a spectacle to see in its own right and then conversely when it's at its southernmost point then it will be low down it'll rise at its low most southeasterly point and set at its most south westerly one and never get very high in the sky at all even the time it's up that's so interesting so what can you tell us more generally about

the moon's orbit well the moon's orbit is like the orbit of other things and we tend to i guess we get taught as kids that there's some sort of neat symmetry in the universe and that planets go around stars in in perfect circles and moons do the same around planets and of course it's just not that neat it's not like that the moon orbits the earth in an ellipse which is a squashed circle and so that means that it's sometimes closer and sometimes further away so you do get a change a small change not a huge one but a small change of about 15 in the size of the moon or the appearance of the size of the moon and its orbit around the earth is also tilted compared with the earth's orbit around the sun and so that tilted orbit also in a complication which connects with the standstill that processes

over time which means that it kind of wobbles round over the well i say wobbles implies something unstable it it drifts round over that 18.6 year period and so my feeling about it overall is that it's it's actually all quite elegant but it's a lot more complicated than you think at first sight so you know you might imagine all these great circles they're just not like that you know they're ellipses and they're tilted and they move around. So things are just a bit more complicated than you might imagine. And what timeframe are we looking at there for, you know, the moon and how that changes? Well, yeah, so it goes round the Earth roughly once a month. It depends on how you measure it, whether you measure it by the phase of the moon, which is about 29 and a half days, or you measure it with respect to the stars.

From memory, 27 and a half or so slight difference there um but uh on the there are the and that then would give you say full moon to full moon so 29 and a half days uh you also it will go through those changes in distance over that period as well so if you look at it then um when it's closest to the earth then two weeks later a bit at its furthest points from the Earth. These are called perigee and apogee. And, you know, that explains the changing appearance as well. Now, the longer time scales are more complicated and they just are that there's this slow drift in those parameters over a longer period. So the 18.6 year cycle in the case of the standstill.

OK, that makes a lot of sense. six-year cycle in the case of the standstill okay that makes a lot of sense now i don't know about you becky but i remember summer holidays camping as a child we would drive down to somerset and i would be so excited as we'd go past stonehenge it's just such an incredible sight it's wrapped in history and quite a bit of mystery that's spanning the last 4,500 years. I mean, yeah, it's spectacular, Izzy, but I love how that's your prevailing memory of Stonehenge. Mine is just getting stuck in traffic constantly around it because we have to drive past it so often to get to where my sister lives. I was just like, ah, Stonehenge. Anyway, if you've never seen Stonehenge or been stuck in traffic next to it, it's an iconic stone circle and once upon a time had four stones, also known as station stones, and they were arranged in a rectangle on the outer edges. Now, the site is a masterpiece of engineering and building. It would have taken a huge effort from hundreds of well-organized people using only the simplest of tools and technologies.

using only the simplest of tools and technologies. And people famously gather at the site for sunrise on summer solstice. But what connection does it have to the moon? Well, this is something a group of universities in the UK, the Royal Astronomical Society and English Heritage are studying at Stonehenge. We're going to hear from those teams, starting with Heather Sabir, the senior property curator of Stonehenge who recorded something for us as she actually walked through the site. I'm here at Stonehenge on a beautiful sunny morning just standing by the heel stone which is one of the

stones that's furthest from the main circle but leads the way up past another stone that's on the ground called the slaughter stone which was named by antiquarians because it looks a little bit red and then I'm just standing now in front of the eiter circle of giant sarsens these are the huge pieces of sandstone that make the eiter circle with the lintels on the top and I'm just moving into Stonehenge itself, into the centre of the circle. Immediately in front of me are the smaller stones called the blue stones. They're not really blue, although some of them do have a greenish tinge when they're wet. And we know definitely now that they came from West Wales, over 200 miles away to the west of where Stonehenge stands today.

And they're almost more human-sized, and we think that they were one of the earliest components to come into Stonehenge. The first feature is a bank and a ditch, which would have been gleaming white on the landscape because they would have been cutting into chalk. And associated with that bank and ditch, which is dated to around 3000 BC, the huge stones, they're very dense sandstone. And we think they came in around about 2500. And what we have, what I'm seeing in front of me is a huge horseshoe of giant trilithons. Now that just means three stones,

two uprights with a lintel on the top. And there were five of them facing down what we know as the solstice alignment. Now what that means is on midsummer morning, midsummer sunrise, the sun shines right into the centre of Stonehenge from the northeastern horizon. But we think possibly more important was if you're standing in the centre of the circle by a stone we know as the altar stone, you could have watched the midwinter sunset dropping to the southwest horizon. We think the people that built Stonehenge probably knew that was the turning of the year, that the days would probably get longer because these people were growing their own food. They were the first agricultural Australia.

And so there were farmers and they would have been very tuned in to the weather and the seasons. This year, of course, we're in the middle of a lunar standstill, and there's lots of archaeoastronomers who are wanting to observe the movements of the moon over Stonehenge and see if there's any significance to its position. There's some thought that it might hover over what are known as the station stones, which are four outliers that form a rectangle around the stone circle. And we're all looking forward to hearing if the archaeoastronomers are convinced by observing the moon rising and setting throughout this year, whether Stonehenge will in fact be shown to have a lunar significance as well as a solar one.

One of those archaeoastronomers is Dr Amanda Chadburn, Visiting Fellow at the University of Bournemouth. So what exactly are these teams looking for? teams looking for? So what we're trying to do is to have a look at the possible sight lines that exist in the architecture at Stonehenge and to see whether we can learn anything more about the monument, whether we think it's accurate because there's some doubt as to whether it really is reflected in the architecture of Stonehenge. And just to take this rare opportunity to look and observe the moon in these unusual positions. And when you say sight lines, what exactly do you mean by that? OK, if you stand some distance behind one megalith, a standing stone, there's another one. And then in the far distance, there would be the rising or setting moon. So people can look

along the line that is marked out by these stones and on the horizon would appear or disappear the moon rising or setting on the horizon. So that's what we mean by a sight line. People would stand behind the stones. They could line up these two stones, and the theory is that the rising or setting moon should be exactly on the horizon. I see. Okay, so what measurements are you taking? What are you looking for? And how are you taking these measurements? And how are you taking these measurements? First of all, we're looking at the archaeological data. We are pretty sure that this thing called the station stone rectangle, which are four stones of which two remain, relate to these lunar positions. So what we're making sure of is that the missing stones, we've understood those positions. Once we've established that, we are then able to put our camera tripods there to observe

ourselves, the lunar setting rising in these rare occasions to understand whether this alignment is correct, if you want to put it that way. whether this alignment is correct, if you want to put it that way. Okay. And when are you taking these measurements? Are there some days that are more important than others? You know, do you have to get your timings right? Yes, doesn't matter so much what phase the moon is at, although obviously the fuller it is, is at, although obviously the fuller it is, in a sense, it's sort of easier to see. But even when the moon is quite, well, it's not full, then it's still worth looking to see whether these crescent moons appear along this sight line, this alignment, this imaginary line. And there are phases from full to, you know, crescent, and we're looking at all of them yeah

and so you know obviously you're taking so many different measurements you're looking at the alignment and you're measuring that with telescopes and cameras and seeing how the moon lines up with these station stones in the stone circle and what are you hoping that it can tell us? I think if we can investigate and understand that the moon could have been a real possibility, that we have seen it, even if it's slightly over where it would have been two and a half thousand years BC, then we'll be able to understand a little bit more about whether this could have been an intentional design within the architecture of Stonehenge. My hunch is it was architecturally significant. The long sides of the rectangle sort of graze the circle, the stone circle inside. And so the two long parallel sides are the most southerly moonrise the most northerly moon

set but at 90 degrees if you flip around that is the solstitial axis you're looking at the mid summer sunrise midwinter sunset the design of Stonehenge if you like you've got this rectangle you've got a circle a stone circle fitting really beautifully just inside that rectangle in the centre of the rectangle. And then inside the stone circle, you've got the great horseshoe of trilithons. And that has the solstitial axis running through it in a very regular way where the sun rises at midsummer and sets at midwinter. So I think it was architecturally significant, but we don't know that. And we're hoping that this will just allow us more observations to make us understand how likely this was or whether

it wasn't as accurate as we thought it was. The teens will be taking measurements across the next year, but let's go back to Heather for the final word. I asked her what she hoped the relationship between the moon and Stonehenge might show. One of the things that would be really interesting is if they can pinpoint anything that would suggest that the moon observation might have had significance to the early phase of Stonehenge when the Beinckenditsch was built and there were possibly the smaller blue stones before the huge Sarsen uprights come in. And in fact, on the southeastern side of the circle, where the southernmost moon rise is one of the things they're observing. They wonder whether that was why there are more cremation burials on that side, that it could

have been that they buried them at night in the dark or that the moon with passing of life, maybe there was more significance to the moon rather than the bright day sunlight when you're burying your dead or cremating your dead. I mean, unfortunately, you know, we can only surmise about a lot of this, but it would be really interesting if they could pinpoint whether the moon had any significance for that early part of the site.

Thank you so much to Heather Sabir and Amanda Chadburn. Okay, Becky. So can we just talk about phases of the moon? Because I think it's something that we just all take for granted. They happen, we see them change, but why do we get those different phases of the moon? So the phases of the moon are just caused

by what angle the moon is lit by the sun. So just as it moves around its orbit around the earth. So when it's in the opposite direction in the sky from the sun. So just as it moves around its orbit around the earth. So when it's in the opposite direction in the sky from the sun, we see it fully lit from the front, right? So the near side of the moon to us is fully lit. So we see a full moon, the whole of the moon is lit. But two weeks later, the moon has moved around its orbit and it's now in the same direction in the sky as the sun which means the side of the moon that's furthest away from us that we can't see is now lit up right so we don't see

anything that's lit up we only see the near side of the moon the one that's facing us which is completely dark and so we get a new moon so we don't see any moon in the sky when it's a new moon and so then in the weeks between full and new the moon slowly moves around its orbit it gets more of the near side lit as that angle to the sun changes and so we see crescent moons and half moons before it's fully lit once more from our perspective yeah okay but then we have those things like super moons and blue moons which you know let's face it a lot of articles really blow up into these massive deals but what is happening in those events because they're not they they are a bit more unique yeah so as robert said earlier right the moon's orbit isn't a perfect circle it's oval shaped right so sometimes the

moon is closer to us and sometimes it's further away so when it's closest it's around about 360 000 kilometers away from earth and we call that perigee. That's the scientific name. But more colloquially, we call it a supermoon. And similarly, when it's furthest away, it can get at around about 405,000 kilometers. We call that apogee or a micromoon. New favorite term. Hello.

Micromoon. I thought you'd like that. Now with the eye, it's really hard to discern any difference right like that you can't tell the difference between a normal moon and a super moon or a micro moon like you don't have like a normal moon next to a super moon to compare it to so i think you're right there's just been far too much hype about super moons in the media to be honest i think the media are just looking for anything cheerful that they can report on um and this is why often you see the people picking up on the idea that there's going to be

a blue moon as well so i think first off we should say a blue moon is not blue um it's just the name that we give to this sort of quirk of when the moon's orbit lines up with our calendar so like what months are 30 to 31 days long but the moon's orbit takes roughly 27 days. So the traditional definition of a blue moon is when you get four full moons in one three-month season. So like spring is three months, summer is three months, right? And sometimes you might get four full moons in like spring, summer, whatever. And because you can get one like early on in the season, right? And then you can sneak in a fourth one at the end if everything just lines up right. But then you'd also hear people recently, like a second definition is sort of cropped up,

which actually just stems from misunderstanding the traditional definition. And it's that a blue moon is when two full moons happen in a calendar month again, because a calendar month can be like 30 days, the moon's orbit is 27 days. So you could get a full moon at the beginning of the month and a full moon at the end of the month. Okay. And you've mentioned that you can't really tell the difference between a super moon and a normal moon.

But when you look at it, they do look massive. So what is going on? I mean, right, is was the moon low down in the sky when you saw it as a supermoon correct maybe near some trees or buildings yeah yeah yeah yeah yeah okay so this is called the moon illusion right so the moon looks bigger closer to the horizon but it's been proved many many times in many different ways that it is actually the same size wherever it is on the sky right you can do this if you know, keen astrophotographer, you can take many images of the moon as it rises or sets, and you'll notice it is the same size in

every image that you take if you overlay them. Or you can even do it just by blocking out the moon with something like holding something at arm's length, right? Like you can pick up a pebble off the ground that's about the same size as when you line it up, or you can just use one of your fingers to do it as well. And you'll notice if you do that when it's lower to the horizon and when it's right above your head it's still the exact same size compared to like the pebble or your finger whatever you're using it and this has been recorded for centuries like by many different cultures as well and there's been lots of ideas raised for how to explain the moon illusion like some people have suggested it's because you know you have like sizes of buildings to compare it to so it looks big in comparison to something that you're

used to seeing every day. And then some people have suggested, okay, it's just a perspective thing. So if you think about like clouds that you see in the sky, like directly above you, a cloud looks much bigger, right? Because it's much closer to you than a cloud that's further away on the horizon, which look much smaller, but you know it's much closer to you than a cloud that's further away on the horizon, which look much smaller, but roughly approximately the same size. So if the moon is closer to the clouds that are closer to us, it looks smaller because the clouds look bigger. Whereas if the moon is low in the sky and appears to be near the distant clouds that look smaller than normal, the moon looks bigger in comparison, right? But even with all of these ideas out there,

there's still no agreed on reason for the moon illusion still. We just know that it happens, we know that it, we think that it appears bigger, but it actually doesn't. Stonehenge is one significant place tied to the moon's orbit, but it's not the only one in the world. There's also Chimney Rock in southwestern Colorado in the USA, and it's part of this same research project with Stonehenge. Now, Chimney Rock is a long, narrow ridge that rises up thousands of feet above the surrounding river valleys. And at the very end of it are these two big rock formations, also known as pinnacles, that stand like pillars with a gap in between them. During a lunar standstill, the moon lines up perfectly in the gap in between those pillars.

But as you might imagine for a ridge that rises up thousands of feet above any of the surrounding river valleys, it's not the most accessible of places to see such a phenomenon. Yet Native Americans have been living there for thousands of years. I spoke with Dr. Erica Ellingson, professor at the University of Colorado, who studies chimney rock and what it means to these communities. Chimney rock has been an important place for Native American people for millennia. We see evidence that people have lived in the river valley, but also have built structures up in the upper areas up on the knife ridge the places with the really extraordinary dramatic view between the

pinnacles. The Pueblo people are associated with the Chaco civilization that flourished about 100 miles away in Chaco Canyon. This is a place where we know there was a lot of astronomical observation and understanding, knowledge of the sky. The sky was very important to the people of that civilization. Between 900 and about 1100 AD, the ancestors of the Pueblo people built a quite dramatic multi-storied building and sets of ritual spaces what the round space is called kivas and this very difficult to access place very very high up onto the ridge it's a little difficult to understand why they would choose to build a place up there except for very possibly the dramatic views and that feeling of being lofted up into the sky. And so it was, of course, very easy to imagine that Chimney Rock was a place

where people would gather to absorb the sky, to look at the sky, to observe it. And so when it comes to Chimney Rock, what does that have in relationship to how the moon moves? At Chimney Rock, you could stand up on that very, very narrow ridge, you know, with cliffs surrounding you on all sides, looking up at the chimney and say, well, where would I have to stand for the sun to rise between the pillars? The answer is you would have to walk off to one side

and fall off the edge of the cliff. And so my colleague, Kim Melville at the University of Colorado worked it out that the moon, when it is in its most extreme northern positions during the major lunar standstill seasons, there is a possibility that the moon might be something that would have been a feature, would have been a very dramatic view that could be seen from the knife edge ridge up at Chimney Rock and the Great House and the Kivas there as well. That's fascinating. And actually, I'd like to talk about those structures a little bit more because tell us why they are interesting

when it comes to that cycle of a major lunar standstill. Well, one of the things that makes us believe that a little bit more physical evidence that the Moon was associated with the building of these buildings was that when you do the tree ring dating, the dendrochronology of beams within the ancient structures, what you find is that the beams were cut and ostensibly the buildings were built or renovated on dates associated with lunar standstills a thousand years ago. And so this cadence of rebuilding, refurbishing these buildings seems associated with the recognition of the moon coming back and rising is the recognition, the feeling that we have all been linked to moon watching, that people a thousand years ago recognized these cycles, observed these cycles, had these experiences, these human experiences with the sky a thousand years ago in this truly magnificent setting. a thousand years ago in this truly magnificent setting. And to be able to witness that,

to share that feeling a thousand years later is really a remarkable, a remarkable experience. Amazing. And so does that echo through to communities today as well? We're about to approach this cycle of the moon being at its extreme. So what will be happening today in Chimney Rock to mark that? The Chimney Rock area really still holds very deep spiritual significance for modern Pueblo and other tribal communities. There are 26 tribes and Pueblos that are associated traditionally with the Chimney Rock area. 26 tribes and pueblos that are associated traditionally with the Chimney Rock area. And the descendants of the ancestral Pueblo people, they do still return to this place today in order to perform ceremonial or traditional purposes. In fact, the Chimney Rock area is seen as really a source of traditional cultural materials, including medicinal plants and other materials

that are collected by tribal leaders for food and medicine today. And so there is a real recognition that Chimney Rock continues to be an important place for the Pueblo people and the tribal people, the tribal Native Americans today. A moonrise at most times is a lovely thing to see, but I can imagine that seeing it at Chimney Rock is even more breathtaking, especially when it fits in between those two pillars. Is that something that people can see? Because of the lunar standstill season that is coming up in

2024 and 2025, my colleagues and I at the University of Colorado have been working with a consortium, including the US Forest Service, which manages the Chimney Rock, which is a U.S. national monument, along with the Griffith Observatory in Los Angeles and Lowell Observatory in Flagstaff, Arizona. working together to make educational materials about the lunar standstill, including a really fun project about trying to bring the experience of watching the moon between the pinnacles to a wider audience. I described the place you would stand to watch the lunar standstill, but to give you a little more detail, if you could imagine a place maybe about 12 feet wide with thousand foot cliffs on either side and in front of you. And so this is not a place where you want to bring a lot of people up in the middle of the night to watch moonrise. And so what we have done is in this very remote place, we have brought a satellite link in backpacks up to the top of the ridge and have been demonstrating that we actually

can live broadcast the moonrise as seen from there. So we are planning a series of events coming up next September and October where we hope to gather people into our accessible amphitheater down in the river valley below hand and have a moonrise event where we could share live stream moonrise of the moon between chimney rock along with the other moonrise that I hope that we could get people to share with us this experience of being together watching the moonrise. And so even though we can't bring a lot of people onto the summit of Chimney Rock to see the moon rise, I do hope that recognising that these special moon rises are happening and gathering perhaps in a safer spot to celebrate that will be a significant and a satisfying experience. Thank you to Erica Ellingson. And we'll make sure that we put any links to where you can view all of these moon rises in our show notes so make sure you take a look at that. This is the Supermassive podcast from the Royal Astronomical Society with me astrophysicist Dr Becky Smethurst and the science

journalist Izzy Clark. This month we're exploring the lunar standstill and the different phases of the moon but before we get on to the questions, obviously, Robert, this is a project that the Royal Astronomical Society is really heavily involved in. So from your point of view, what are the activities and the things that you're doing and contributing to this side of the project? Well, the biggest thing we want to do is really to get the message out there to the public that this is this is an intriguing thing to see in the sky. You know, firstly, you can look at it. And if you I guess it's like knowing, oh, wow, the moon is actually unusually high in the sky or unusually low. Or there's this very dramatic moon rises and moon sets. And also that it does have this historical resonance, too, that our ancestors may well have understood it, too. You know, they had a long enough generational memory

that they saw this change in the way the moon appeared in the sky over time. Now, sure, they wouldn't have understood anything about orbits or the fact that, you know, things were moving around the sun and moving around the Earth rather than the whole universe moving around the Earth. But the very fact they could mark it is really significant. So we're trying to do things that will help promote the live stream. We'll be involved. We're hoping to do, you know know filming on site and that kind of thing and promote events to actually

observe it later in the year as well so that's the sort of thing we want to do really support the research work and get the public interested in this too and excited because you can you know you don't have to go to Stonehenge to see this if you've got a decent horizon you can see it wherever you are in the UK and you can experience it and look and think, oh, wow, you know, this is unusually north, unusually south. I would really love to see some very dramatic pictures of the full moon, moonrise, for example. That kind of thing is always great to see as well. I feel like I'm going to be getting out the telescope very, very soon. I think you are.

I think you are. Well, in the summer as well, it's great, isn't it? You know, when this thing's happening in the summer too, you can go out and it's a ideally you know we've actually had some nice weather recently right so go out in balmy weather and sit there you know i shouldn't be too facetious about this but with the drink on one hand and your smartphone in the other okay so let's get on to everyone's questions and i just need to set the record straight for everyone who asked no the moon is not made of cheese. Honestly, it was one of the most popular questions in our Instagram. I should have expected no less.

I mean, I really enjoyed it, to be fair. Like, I'm not criticizing anyone. It really made me laugh. But listener Jonathan Mound has been in touch with an actual paper by Schreiber and Anderson that was published in Science and that was about the properties and compositions of lunar materials earth analogies and according to that data and depending on which moon rock you're looking at the most similar analog is either Norwegian brown cheese or Munster. So brilliant. I'll think about that next time I eat some Munster. Exactly.

Okay, so let's get on to the actual questions. Becky Zedbot007 asks, why is the moon tidally locked with Earth? Good question. So, I mean, tidally locked means it's like the moon and Earth are two friends with their arms outstretched, holding hands and spinning around, right? It means that the moon takes the same time to spin on its axis as it does to orbit the earth so we only see one side of the moon like the near side so same as if the analogy

with the two friends holding hands like we only ever see the moon's you know face and not the back of its head now why this, is thought to be because of how the moon formed in what's known as the giant impact hypothesis, or I quite like the phrase, the big splat, as some people call it. So Earth's moon is thought to have formed when a massive object, so like another proto planet in the early solar system, collided with Earth, throwing like molten rock debris everywhere and this was sort of like billions of years ago four billion years ago or so the moon then formed when that all that molten rock debris clumped together under gravity and that would have then been spinning

wildly just due to all of the chaos and the forces at play and so it would have been much closer to earth than it is today as well because that molten rock would have been close to Earth where it was thrown out. And it would have been pulled into sort of an egg shape as it orbits the Earth because it was so close to it, sort of like an American football, right, with a bulge in the rock pointing towards Earth, like the tides, in the ocean today, but in moon rock rather than in water, right? And that lump was moving all the time as the moon spinned, right? And the side of the moon that was always facing the earth ended up having that bulge pulled towards the earth. And so that pulling on the moon shape as it changed and moved around its orbit would have heated up the moon which meant that it lost that

energy to space and as it loses energy it then slows down its spin until you know a single spin on the moon's axis took the same amount of time as one trip around the earth and at that point right if there's a bulge on the moon of that moon rock being pulled towards the earth that's no longer like moving relative to the earth it's in the same place and so there's no more energy being lost and the spin rate stops changing and that's what's left in this tidally locked state amazing thanks becky and robert we've had lots of variations of this question and it's about the moon moving away from us so thank you if you sent in a question about that i'm going to combine them here so the question is why is the

moon moving away from us and would that impact eclipses yeah great questions which of course also means they're complicated as you know by now um so as the moon orbits the earth it raises ocean tides twice a day as does the sun by the way but the but the point is that that that happens and the rotation of the earth as a consequence is slowing down too over a very very long period of time it took billions of years to be really significant and that kind of loss of energy this coupling between the moon the ocean tides and the rotation of the earth transfers energy to the motion of the moon so you have to imagine that the moon gains the miss it's sort of like the tidal bulges that imagine the oceans piled up in the tides pull on the earth a bit and give it a bit of a kick or the moon a bit rather and give

it a bit of a kick and if you give it a bit more orbital energy then what will happen is that it moves away from the earth and we can measure this really accurately thanks to experiments that were left behind by the Apollo astronauts, by the Soviet Union with their Lunokhod rover missions, and actually more recently by India's Chandrayaan-3 lander. And all of these placed these reflecting panels on the lunar surface. So very simple things, just reflecting panels. And they're some of the most successful experiments left behind on the surface of the moon. And the ones in the Apollo landers are still working after 50 years more than 50 years and scientists can then fire lasers from the earth to the moon and they time

how long it takes for the laser to go to the moon and back and if you know the speed of light then you can work out very accurately how far the moon is and over time then we've been able to calculate that the moon is moving away at about 3.8 centimetres a year. So not very far really, very, very, a very, very small amount. But over millions of years, that obviously adds up. And running the clock forward, it will eventually indeed have an effect on solar eclipses in particular. So at the moment, we have what are called annular eclipses, which is where the moon is too far away to completely cover the sun, you get a ring of sunlight left around it. And then total solar eclipses, which are more exciting whereby the whole moon the whole sun rather the whole bright photosphere of the sun the solar disk is covered by the moon and that's when you see the

outer atmosphere the corona all the stuff people saw in the u.s back in april and were understandably justifiedly really enthusiastic about in about 600 million years time the moon will not be close will never get close enough to completely cover the solar disk so there will be no more total solar eclipses only annular ones but you know that's a really long time away and the earth may not it's possible the earth may not even be habitable by that time anyway so i think we've got other things to worry about we've got many many millions of years of total solar eclipses to come okay thanks robert i'm becky hazel underscore c82 wants to know if the moon was slightly bigger or smaller how would that impact yeah this is a great question hazel like the moon being a different size would actually have a massive effect on earth like more than

you would necessarily think right i think tides is perhaps the obvious one. So larger or smaller tides would have a really big impact on sea life, right? Because the tides distribute nutrients around the oceans. They also leave behind rock pools, you know, tide pools, which, you know, if you had smaller tides, you wouldn't necessarily get as many, which, you know, some researchers think that life first evolved from those kind of tide pools as well. If you did sort of increase the size of the moon so that it would be much more massive, that would lead to also larger tidal differences, right? So bigger high tides, smaller lower tides.

And so you'd probably get a lot more like coastal erosion, coastal flooding and storms in coastal regions as well, which again are big places that you find life on earth so also if you have a larger moon that would also change the rate that earth is spinning at as well and the smaller moon would change that rate less so that would actually affect how long our day is which is crazy oh my gosh yeah of course it's all to do with that sort of exchange of energy that robert and i were talking about before as well you know about sort of like this whole process of things moving away from us and the Earth's day getting shorter as well. So that would obviously change like how we live our lives if we had, you know, sort of longer or shorter days. Plus, the moon also stabilizes the Earth's axis tilt, you know, the tilt of like 23 degrees that gives us our seasons when the northern hemisphere points towards the sun, we have summer. And when the northern hemisphereisphere points towards the sun, we have summer. And when the Northern Hemisphere points away from the sun,

we have winter. If we had a different size moon, we could end up with a different tilt. So if there's like a smaller moon, you know, maybe the tilt wouldn't be as stable. You would have a larger tilt. You'd have more extreme seasons with like more extreme temperature differences

and weather differences. Or if you even have a larger moon, perhaps you have less of a tilt because it's held more stable so you get less seasonal change right so it's just so much to think about and you know some people have argued that even having a different size moon might have meant that life didn't evolve on earth or at least not in the same way as it has so i think really interesting question from hazel there great question oh my god great question it impacts us in so many different ways. Okay.

You just think, oh, it's just like they were in the sky. And you're like, nope. Yeah. I mean, yeah, it's interesting because my brain went, oh yeah, the tides would be different. But then you're like, oh yeah, but the impact of different tides is also a very important thing. Okay, great question, Hazel.

And Robert J. Denmark says, thing um okay great question hazel and robert jay denmark says why is the moon's near side so different from its far side yeah jay denmark this is something of an enduring question with various explanations put forward now the context here is that until the space age we could reasonably have assumed that the side of the moon seen from the earth we can actually see about 59% of the surface over time because there's an effect called libration um and the far side of the moon is seen from the earth we can actually see about 59% of the surface over time because there's an effect called libration and the far side of the moon would be quite similar in appearance but from the space age starting right back with the lunar 3 mission in 1959 that was a soviet mission we had pictures of the far side of the moon and they showed how different it is so the far side has lots of craters and it doesn't have these big

lava planes so if you look at it it does indeed look very very different from the near side that was one of the definitely one of the surprises of the space age now the idea for why there's those differences that there are various hypotheses performed one is that there was a large impact early in the history solar system after the moon had formed, and it led to some pile-up of material on the far side, because it also has a much thicker crust. And also that not long after the Moon was formed in this debris from this giant collision between the proto-Earth, sometimes called Theia, and a Mars-sized body, that you have to imagine you've got the Moon cooling down,

or this rocky body there, much smaller than the Earth, and you've got possibly this very hot molten earth left there as well one idea is that the near side was heated by the molten earth and that helped with these these lava planes stick around and then there's also an argument that the lava planes have got higher concentrations of radioactive elements in them and they they provide a heating effect and that might have helped to keep them molten for longer but i think you can see i'm offering multiple explanations because i'm not sure there's a really good consensus on this yet it's a really interesting question to explore thank you robert and thank you to everyone who sent in their questions please do keep sending them in you

can email podcast at ras.ac.uk or find us on instagram and send it that way it's at supermassive pod um so robert let's finish up as usual with some stargazing what can we see in the night sky this month is it a good month for the moon uh well it's it's actually it's a good month for the sun really so you've got the the summer the summer solstice or i should say just the the June solstice on the 20th of June. And that means in northern latitudes, you get the shortest nights of the year. And in southern latitudes, you get the longest. So for anybody listening, Australia, New Zealand, South Africa, South America, etc. You know, you're getting into winter there.

Now, from the UK, it never gets properly dark because the sun is never more than eight, never reaches 18 degrees below the horizon, which is the definition of proper darkness when we have astronomical twilight ends. And so what you'll notice if you go and look at the night sky this time of year is that it isn't as dark as the winter and you see this glow in the northern horizon as well. And that's particularly pronounced if you're, say, up in the Shetlands or the Orkneys or the far north of the UK, you know, even more of a pronounced effect up there. But some of the bonuses from that are you can see things like these noctilucent clouds, which are clouds that appear to be glowing in the middle of the night because they're so high up.

They're in the north, 80 kilometres high, really, really high by the standards of clouds, the highest ones in the Earth's atmosphere. And they catch that sunlight in that part of the sky, even in the middle of the night. And they're really incredibly beautiful if you see them. And there are some wonderful photos you see so and they tend to be around from June to September each year so do take a look for those you can see stars still yeah um quite as well but still pretty good and June is a time to catch those spring stars that are still there so Ursa Major and the Plough are high overhead early in the night Arcturus that

bright star is obvious and Spiker and virgo lower down and you can also see things like the red giant antares which is in the bit of scorpius that's visible from the uk because some of it isn't it's quite low down that'll be low in the southeast and that gives you a hint of this summer milky way which is fantastic that will be coming a bit later in the year or better later in the year july and august it's particularly good and on into september and october and if you want planets they're there but there are things you have to get up for early or better later in the year, July and August, it's particularly good, and on into September and October. And if you want planets, they're there, but they're things you have to get up for early in the morning rather than in the evening sky.

But if you are up and about after 1 o'clock, 2 o'clock, 3 in the morning, you can see Saturn, and then later in the month, Jupiter will become visible. And on the 3rd of June, there's a nice photo op if you get up before dawn where you've got the crescent moon next to Mars. Mars is not particularly good through a telescope at the moment. It far from the earth but it's there next to the crescent moon a nice photo op and jupiter further over and that'll be in the southeastern sky before dawn but as i said at the start this is really a good time to be looking at the sun now solar activity is really high we've had these big sunspot groups the one that led to the wonderful display of Northern Lights a month ago.

And my strong recommendation is to look for those. Now, you have to do that safely. So it's worth investing in a certified solar filter if you have a telescope. Check out a proper astronomy supply. I mean, this is what I would do. Don't rely on anything cheap. It's your eyes you're talking about here. I mean, this is what I would do. Don't rely on anything cheap. It's your eyes you're talking about here. And then you add that to the big end to be, you know, to put it in simple terms of what's called the objective of the telescope. If you've got a telescope and you can get similar things with binoculars. And then if you use that properly, you can see sunspot groups growing and shrinking. And you can watch the sun rotate from one day to the next as they move around because that's marking the rotation.

And I think that's a really really nice thing to do in this warmer weather and you know a nice aspect of daytime astronomy which is obviously also uh very convenient to yeah absolutely my god my telescope won't know what's hit it i've it's gonna get used yeah yeah i've got one of those uh filters that you do you screw it onto the end and it's brilliant um it's it's just so good if you do want to go and have a look at the sun um okay well thanks robert and i think that is it for this month we'll be back next time with and it's brilliant. It's just so good if you do want to go and have a look at the sun. Okay, well, thanks, Robert. And I think that is it for this month.

We'll be back next time with another bonus episode. And after that, we've got a special on black holes. It's going to be a Q&A. So get your questions in and no doubt Becky is going to be very excited about that. Oh, so excited.

I mean, do I need to revise? No, I think I'm probably good. I'm so excited for that one I need to revise no I think I'm probably good um yeah I'm so excited for that one mainly because our listeners just they think of the best questions that like you're so ingrained in a topic that you don't think to ask anymore if that makes sense so yeah I'm really excited for that one and to be honest it's been a long time coming as when we go into that when we go into the mailbox I'm like every other question is about black holes. And I'm like, we actually need to go back to this topic, don't we?

Yes. So we're doing it. We're doing it next time. Unleash me on the mailbox. Yeah. All right. So look out for that one, everyone. And contact us if you try some astronomy at home.

It's at supermassivepod on Instagram, or you can email your questions to podcast at ras.ac.uk. And we'll try and cover them in a future episode but until next time everybody happy stargazing