The Supermassive Podcast - 42: A (brief) History of Astronomy

Episode Date: June 22, 2023

Dr Becky and Izzie dust-down the Supermassive Tardis to explore the history of astronomy. From fossilised baboon bones and baby lamas to Einstein and black holes, the Supermassive team discovers how we came to understand the Universe the way we do today. Editor Richard talks to astronomer and science writer, Dr Stuart Clark, who reveals where the phrase ‘the dog days of summer’ comes from. And Izzie chats to President of the Royal Astronomical Society, Professor Mike Edmunds, about the amazing Antikythera astronomical calculator. As usual, Dr Robert Massey is on hand to take on your questions.  Stuart’s latest book is Beneath the Night: https://www.amazon.co.uk/Beneath-Night-Stuart-Clark/dp/1783351535 Send your questions or astrophotography to [e-mail], tweet @RoyalAstroSoc, or find us on Instagram @SupermassivePod.  The Supermassive Podcast is a Boffin Media production for The Royal Astronomical Society. The producers are Izzie Clarke and Richard Hollingham. 

Just how long have people tried to study the night sky and work out what it all means? Kepa that really took those laws and then was like, okay, so how does that apply to planets and their orbits? It's a geared astronomical calculator from the first century BC. Hello and welcome to the Supermassive podcast from the Royal Astronomical Society with me, science journalist Izzy Clark and astrophysicist Dr Becky Smithhurst. Last month was all about the future of astronomy, so this month we're going back in time. I know, the Royal Astronomical Society does not have a TARDIS and to my knowledge Becky hasn't discovered a time-bending wormhole yes not not yet at least um to my disappointment because chris hemsworth hasn't popped out of one either like vanatley portman in thor keep working on that keep working on that i will i will you know this was what was sold to me as the life of an

astrophysicist and i'm still waiting for it we're actually looking at the history of astronomy today so how historically we've studied the universe and our place in it. Here with us, as always, is Dr. Robert Massey, the Deputy Director of the Royal Astronomical Society. So Robert, what is the oldest piece in the Royal Astronomical Society's archive? Because you have loads of stuff. We do have loads of stuff. And of course, the obvious thing to do, which I did, was check with our librarian, Dr. Sian Pross prosser and she referred me to a book dating from 1472 called di natura rerum on the nature of things written by isadora of seville and it's a reprint because that because

isadora of seville died in 636 so we wrote it by the time this was published, it was more than 800 years old, despite being 550, if I get it right, years old now. So it's the oldest printed book that we have. And it's a short treatise on physics, astronomy and geography. I have seen this on display and it's fascinating to look at because what you realise is these are incredibly lavish works. I mean, they're obviously a very small minority of people own books at the time. And you can see it has these wonderful, almost cut out models and rotating discs. And another description of the book has been the book of wheels, just to illustrate the way that things are in the sky. And they were obviously thinking about a geocentric universe at the time,

the earth at the center of the universe, but amazing thing to see. So occasionally we have that on display either for special scientific conferences or sometimes when we have things like open house in the autumn. So do look out that actually if you're anywhere near london we'll have our building open in september we might have things like that on display i'm not promising it because shan won't be happy but that's the kind of thing shan fending off people like like no stop indeed she won't thank me if i if i make this play your grabby hands away oh yeah yeah exactly there are there are real limits to who gets to handle it as well. Well, thanks, Robert.

We'll catch up with you later in the show, as usual, for our listener questions. So I think we can all say that at one point or another, we've looked up at the night sky, taken in the view, and have been filled with awe, and then swiftly followed by a lot of questions. So just how long have people tried to study the night sky and work out what it all means? Editor Richard Hollingham spoke with our friend, journalist Dr Stuart Clarke,

author of Beneath the Night, How the Stars Have Shaped the History of Humankind, for a whistle-stop tour through history. The evidence, depending on who you believe, could date back to around about 20,000 years ago. There's one particular artefact called the Ishango bone, and this is a fossilised baboon bone that was found in the 1960s in Congo. And it has these markings on it, And they're not really aesthetic markings. They're maybe more like tally marks, somebody counting something. And there are all sorts of ideas for what that might be that they're counting. But one of the ideas is that it's some sort of lunar calendar.

And so it's a sort of a timekeeping device. And there are other sort of ancient artefacts as well, which some people look at and interpret in these kinds of ways. So we don't know for absolutely certain, and there are other things that these could be, but that sort of evidence dates back into essentially prehistoric times. And why would that be? Why would you need a lunar calendar? So I think one of the first and most obvious uses, if you like, for the night sky is timekeeping. You know, we get our night and day from the movement of the sun, we get our month from the

moon, and we get our year from the positions of the stars and keeping a tally I suppose of of where you are in that period and where you are in that time frame because that helps with the seasons the seasons appear to tally with what's going on as well there are also certain social gatherings that we believe that these ancient people would have tied in time to the winter solstice or other astronomical configurations and you know without watches and clocks those were the kind of of of clues visual clues that you had to tell the time and know when to maybe you have to travel across the country to a certain specific gathering or something like that. What about the stars? I mean, we have to talk about when's the evidence that they started to become

important or significant to particular civilizations? Yeah, so those, again, they're linked, if you like. The correlation that's noticed is that the patterns of the constellations change throughout the year and that mirrors the seasons. And so there are a lot of ceremonies that celebrate the reappearance of certain stars or certain star groupings. So in New Zealand, for example, there's the Matariki ceremony, which is the reappearance of the Pleiades, the Seven Sisters star cluster. And then the next new moon after that reappearance of the Pleiades is the Maori New Year. In ancient Egypt, Sirius would rise just before the Nile flooding season. And so there was thought to be some sort of

correlation there. And in fact, we still use a phrase that derives from those times, which are the dog days of summer. And when we say that, we mean the very hottest times of the summer. And that comes from Sirius, the dog star in Canis Major. And the idea was that, well, heat obviously comes from the sun. Sirius is the brightest star in the night sky. And so when Sirius is above the horizon, perhaps its heat was also adding to the Egyptian summers. And that's why it was the hottest time of the year. And so those are the dog days of summer. That's fantastic. Let's talk then a bit more about Egypt.

And I think we need to bring in gods here because there was a tie-up inevitably between the night sky and religion. Talk about the sun in ancient Egypt because I love the way that features and the way that ties in with the gods and what's going on in the heavens. Yeah and I think when you take a step backwards and just think about the sun it's so reasonable that they placed so much emphasis you know and godlike power into the sun because of course it gives life to the planet sunlight drives life and so it seems obvious that it's the life giver it's the the you know the the supreme deity the supreme

force that's controlling everything that's going on on the earth and then of course where does it go at night well they have this concept of Nut, the sky goddess, who has the stars painted on her torso and she swallows the sun at the end of the day and the sun traverses through her body during the night and is reborn at dawn in the mornings. So this idea of the gods and these extremely remote places of power that somehow influence life on Earth is prevalent right from the very sort of first recorded writings, which come from the Mesopotamia region. And there was a city there called Kesh and the Kesh Temple Hymn, one of the earliest pieces of writing. temple hymn one of the earliest pieces of writing and it celebrates the link between the earth and the heavens and the night sky and suggests really that the temple there is the link between those two realms the other thing that's interesting that happens in the egyptian period is the book of the dead and this is the wide scale way for people to get to heaven as it were.

It develops over centuries in fact and first of all it's only the pharaohs that can ever go up into the night sky and join Ra on his golden chariot crossing the sky every day. And then gradually access to this starry heavenly realm kind of becomes democratized. And the writings of how to get to follow the stars to get to heaven that you see on the pyramid walls in the burial chambers, in the pyramids, they gradually become included in coffins, on the lids, the inside of the lids of coffins for sort of lower and lower classes of people. So access to heaven is democratized, but at the same time, the idea of judgment on whether you are worthy to get into heaven or not, comes in for the very first time. And the idea of weighing of the heart to see if you're pure enough to enter heaven or whether you are devoured by some kind of demonic monster at that point.

When you look at those writings, and writings later than that, and mapping out the stars, are they accurate? Can we use those as an accurate portrayal of how the stars were, how the cosmos was and how it looked like to people thousands of years ago? So the ancient Egyptians, for example, they don't use the constellations that we use. In fact, they use much smaller groupings of stars and these little asterisms, you know, we find them on temples and on carvings, but we can't correlate them with the stars that we see today. They're just too generic, you know, maybe a triangle of stars or something like that.

The constellations that we use, however, they were sort of enshrined by the Greeks and classical antiquity. They almost certainly came from this Mesopotamia region, the sort of the fertile crescent, and the very first civilizations that sprang up there. One of the most interesting things for me are the paintings in the caves at Lascaux. There's the Hall of the Bulls, where there's this one picture of this sort of ancient bull-like creature, an Uruk, and there are dots that surround it. And if you look at the dots, there's a cluster of dots on its face, a cluster of dots above its shoulder, and following its eye line there's a little line of dots. They are excellent representations of the constellations of

Taurus and possibly Orion as well. So the eye of the bull on this cave painting in a 19,000 years old cave painting looks as if it could be the Hyades star cluster with the eye itself being Aldebaran, the star we see as the eye of the bull today. Above the shoulder of this cave painting, another cluster of dots that could be the Pleiades, the seven sisters, a good positional representation for where they are today. And then this line of stars is in about the right place for Orion's belt but there's four stars on the cave painting not three but there it is Taurus an actual depiction of a bull and these dots that could be the stars other people think there are other interpretations

of all we'll never know but it is tantalizing to wonder it's a good point to bring in a question actually from our instagram and apologies for mangling this name and jali vitu red car asks on instagram how did ancient asian civilization understand the universe so we talked about sort of mesopotamia what's now the kind of middle east iran that sort of egypt area what about asia yeah this is fascinating as well and they interpreted the night sky from their own sort of cultural beliefs so for example the chinese i look this up i'm going to read this out so that i don't get this wrong because these are these are lovely sounding things so they split the northern celestial hemisphere into three different regions and because they were a highly imperial culture where the emperor and the imperial palace was the the center of Chinese or that culture society the celestial representation of the imperial palace was up near the northern celestial pole and that was called the purple forbidden enclosure

the imperial court so one removed from that was the another part of the sky which was the supreme palace enclosure and then surrounding that was the heavenly market enclosure so all the rest of the surrounding lands and what is fascinating is that each of the cultures that we look at interpreted the night sky and the various different comings and goings of the stars in some way that was related to their own comings and goings and I think that thought process in survives in um so the the Christian idea the adopted Christian idea of you know as as on earth so it is in heaven and and people were looking um at and cultures were looking at the night sky to try to make meaning of their lives on Earth. It's only much later, millennia later,

that they start looking to try and understand what the celestial objects are. And that, I guess, is my final question. At what point did we start getting it right rather than imposing sort of our culture on on the night sky if you like or taking that as part of our our realm for all of these ancient cultures that they realized that the first step to understanding the wider universe and our place within it was to know the positions of these objects chart the way they moved and so we had

this traditional positional astronomy for millennia that begins to change at around about the 16th 17th century in Europe where we start to look for reasons why the celestial objects might move in the way that they do and that brings in the scientific revolution in which time we start to have dynamics and forces and we start to understand it in a very Newtonian way and then only in the 19th century do we have the breakthrough with spectroscopy in Heidelberg in 1859 which means that we can actually start to analyze the celestial objects for their composition and their physical characteristics and know them as places as it were so it's very very late in the day comparatively that we start

doing what we recognize today as science but in all of those ancient times in the past, they were doing a form of science as they would think of it to try to understand more about the universe. It's just their terms of reference were very different from ours. Thank you to Dr Stuart Clarke. So Becky, is there a particular era that fascinates you? Yeah, I mean, for me, it's sort of like the end of the 1910s and then through the 1920s, which I know was a fairly horrific time for the world in general, but for astronomy, wow,

what a time to be alive. In 1915, you've got Einstein publishing his theory of general relativity. So that completely changes how we think about gravity as a whole. But then you've also got at the same time, the great debate raging, which was this debate between Harlow and Shapley, two astronomers, about the size of the universe, with one believing that the universe was basically just the Milky Way galaxy, and everything we could see was maybe like 100,000 light years away. And then you've got the other arguing that actually you know these fuzzy blobs that we see are actually galaxies of stars in their own right

millions of light years away and that actually culminated in an actual debate in 1920 as well and then through the 20s you got in 1924 it was edwin hubble who actually measured the distances to these fuzzy blobs using lewitt's law and found that they were actually galaxies in their own right. And I can't even imagine living through that era of just going from sort of, you know, this thing about, oh, my entire world view changed. Yeah, your entire universe view changed, you know, where you've gone from thinking that everything is is sort of so close by to being so so much bigger like into terms of you as a human you have shrunk so much more right in terms of what we believe to be the scale of the universe and then of course just a few years later 1929 Hubble then also says the galaxies that are further away from us are moving away from us faster

and so we have the first evidence for the universe expanding so in the space of what like 10 15 years you've gone from hey the universe is just the Milky Way to hey it's much bigger oh hey it's getting bigger all the time I mean talk about a game changer like what a fascinating couple of decades but and I and I think it's something you know from researching this entire episode is something that we take for granted is how much information we have now today but the history and the work that has gone into understanding that and that it wasn't always the case for people i think you can you can forget that i mean i certainly can yeah one fact i love is that we didn't know that black holes existed when we put a man on the moon in 1969.

Like, what? We didn't know we were orbiting one at the centre of the Milky Way, right? Like, at that point. That wasn't until, like, the late 90s that that was accepted. And I, you know, just toddle around in my day job going, there's a black hole at the centre of every galaxy. And just, it's such a sentence I take for granted.

And you have to remember like literally the 100, 200 years worth of research that led up to that point, right? And that's why I love sort of the history of science so much is just being reminded of these facts. Now, an important phase in the history of Western astronomy lies with the Greeks. Most of the stars, planet, constellation

names of the Northern Hemisphere come from the terminology of Greek astronomy. It was an era where we started to see astronomers use geometry to try and understand the night sky. And with that comes the introduction of mechanisms to help them. One such device is called the Antikythera mechanism. It's essentially a mechanical device they use to calculate the positions of astronomical objects. And luckily for us, the president of the Royal Astronomical Society, Professor Mike Edmonds, heads the Antikythera Mechanism Research Project. It's an international collaboration investigating this extraordinary astronomical machine. Well, it's a geared astronomical calculator, really, from the first century BC, made out of bronze. It was found in a shipwreck around 1900, and has always been since then in the National

Archaeological Museum in Athens. It was clear unless we had new experimental data on the thing, we were not going to be able to work out exactly what it did. Describe what this looks like. Is it something that you could hold in your hand or is it, you know, a big mechanism? This one was undoubtedly the handheld, well, not handheld module, but the miniature model, if you like to put it that way. It's about the size of a shoebox. If you imagine a shoebox stood up on its end, that's its size.

Now, on the front, there is a dial that shows you the position of the sun and moon in the zodiac. Remember, the zodiac is the band of the sky around which the sun and moon move. We believe probably it also showed the position of the known planets at that time, but that bit of the mechanism, unfortunately, is missing. On the back of the device, there were two spiral dials, quite intricate. On the back at the top was a spiral dial showing a calendrical cycle, the metonic cycle, which is basically a cycle of new and full moons. What it says, basically, is in 235 lunar months, that's full moon to full moon, there are almost exactly 19 years. So this dial will tell you what basically when full moon is going to be, what date it's going

to fall on. So this device was able to track 19 years in one of its dials? Yes, I mean it's a fairly simple arithmetic relationship, but a useful thing if you want to be able to set out when you're going to have full moon, new moon for religious, political, whatever purposes. On the bottom dial, there was, again, a similar sort of cycle, but this was to do with eclipses. It's a 223-month CEROS cycle.

And what happens if you have an eclipse that occurs, either a solar or lunar eclipse, which could only happen at full or new moon? Well, exactly 223 lunar months later, you'll get a similar eclipse, but shifted in time by eight hours. Now, you don't always see eclipses from the same place, as you know, particularly for solar eclipses. But this dial, which we assume is based on Babylonian observations over time of when there had been eclipses before, can then give you a fairly good idea of when to look out that it's likely that an eclipse might occur that month. Incredible. That's what I wanted to ask you. How would the

Greeks have known what to program and how to build this mechanism and and have that fundamental understanding of the world around us and the planets and you know the phases of the moon well there's a long tradition it goes back way way beyond the Greeks way way beyond the Babylonians and the sites like Stonehenge show clear evidence of knowing about the solstices and therefore the seasonal movements we see from Earth. And the Babylonians, who were before the Greeks and partly co-temporal with them, were very good observers and just naked eye observers. But they kept very good records and worked out what the sequences of things were. Now, the Greeks got into sort of being more mathematical, more geometrical, and began to be able to make models and predictions and so on

and mathematize the observations in different ways. And interesting enough, as I say, this mechanical device was putting this knowledge into mechanical form. And it's interesting to conjecture how far that went and whether, in fact, putting knowledge into mechanical form. And it's interesting to conjecture how far that went and whether, in fact, putting stuff into mechanical form could have pushed their mathematics a bit. If you start thinking about things mechanically, you think about things mathematically in a different way.

So there may have been some symbiosis there. And so when you turned to study this more recently, how did you do that? What sort of scans did you run and what did it find? Basically, we used two major techniques. One was computed x-ray tomography, which basically is just like giving it a body scan, a three-dimensional body scan. You have to use fairly high energy x-rays and we were very lucky that a firm in existence at that time called X-Tech, now part of Nikon, lends us a machine to do that.

The other technique was to do very, very detailed surface imaging with image processing to bring out all the small detail. One of the great things about this device, it not only has these dials, but it has an awful lot of Greek text in and on it, which we were able to read, which helped with the interpretation. Basically, inside, there are gear gear trains at least 33 gears with us main calendrical and solar dials we worked out pretty well i mean a lot of work had been done before but the actual whole trains hadn't been worked out and now everybody agrees about them and And perhaps the most interesting one, if I can talk for a moment about that,

is the lunar train, the one that displays the lunar position in the zodiac on the front and also shows the lunar phase. Wow, so what did it show? The lunar phase was shown by a half-coloured ball. It sort of had two hemispheres. You've seen it on old clocks and goodness knows what, but the invention goes back way way into the past so i'd show you what the lunar phase was now the pointer on the dial

showing where the moon was was quite a complicated train of gears and it had in it a little variable speed device because the moon does not move at the same rate throughout the month. Because as we know now, the lunar orbit is an ellipse. And sometimes it moves faster in the sky, sometimes slower. And the gearing had a device that did that, that allowed the motion to move slightly faster, slightly slower. I must say, what you're doing is you're turning a dial on the side of this device to turn all this stuff. And so whether you'd actually see this difference in rate, I don't know.

But you might just about be able to perceive the difference in rate. But it was in there. And what was so amazingly clever about this, not that it was a mechanical device to give the variable speed, but that little device of four gears was mounted on another gear. What that did was made sure that not only was the amplitude of the variation right, but the period of the variation was right, which is different for the normal lunar month because the ellipse of the moon's orbit processes and it changes the period of this variation. So it's a very, very subtle and beautifully mechanically designed gear train.

It's absolutely amazing. So what would something like this likely to be used for? To be honest with you, we don't really know. We've got quite a lot of references in classical literature, the existence of such devices. It wasn't a one-off. There would have been others of these. There'd have been more simple ones and so on.

So there were undoubtedly quite a few of these devices around. We don't think it was probably a computer for an astronomer to make really accurate calculations. I've done some work on trying to work out how accurate it would have been, and it was pretty good. But if you'd used it, say, for predicting a new moon, you'd be out typically by a day or two. So what is it? Is it a teaching device? That's possible. Was it something you displayed in a temple? That's possible, I suppose. The one I like probably best is that it's a statement.

It's a statement about what we know about the universe. And maybe that's something that people would pay money for to have on their mantel shelf to show, look, I'm really interested in the universe. Here's what's currently known about it. And what is also very interesting about this, the astronomy that is in this device is exactly right for around 100 BC. There's a book by a guy called Geminus called The Phenomenon. And the astronomy in that book from around 100 BC is almost exactly the same as the astronomy that is in this mechanism. So we've got very good reason to believe that this is what they knew about current astronomy. And maybe it was just a way of displaying what they knew about the current state of the universe. Finally, are there any questions

that you still want to uncover when it comes to the Antikythera mechanism? Well, the things one would like to know is how they displayed the planets. We've got a good idea, but that part of the mechanism is missing. It would be interesting to know how they did it. It would be interesting to know how they did it. It would be interesting to know why they did this,

what it really was used for, would be fun. And, of course, the other interesting thing would be, did they have any other kind of mechanical device that we don't know about? We'll just have to wait and see if somebody found one, I suppose. And if I can make one last comment, one of the fascinating things I find is that, at that time, Greek astronomy knew an awful lot about the motion of the planets, but they didn't know why. And interestingly enough, we've

come to the same state again in cosmology. We've got an awful lot of information about the way the universe is behaving. It's increasing acceleration, it's dark matter, dark energy. But again, we're back to a state where we don't know why. Let's hope it's not another 1500 years before somebody works it out. This is the Supermassive podcast from the Royal Astronomical Society with me, astrophysicist Dr Becky Smethurst and with science journalist Izzy Clark. This month, we're attempting to travel through time to understand the history of astronomy. Before we get to our listener questions though I think we've covered quite a lot of ancient history here but when did we start having

a fully mathematical understanding of our universe? Robert, Becky who were the key figures in that? Well it's an interesting question, actually, in how you define fully mathematical. Even if you look back a thousand years, you've got people like Ibn al-Halhith, an Egyptian astronomer, who developed things like Fermat's theorem and the laws in optics and also tried to develop a mathematical understanding of the solar system, albeit sort of aligned to this model still of the Earth

being at the centre of the universe. But the sem change i guess comes in the european renaissance when you look at the the invention of the telescope which was a huge driver and the century before that when you've got things like copernicus re-establishing the idea of the sun being at the center of the universe or the solar system at least and then moving on to people like Kepler and Galileo and Newton, and attempting to, by a combination of observation, developing mathematical theories, actually for the first time making it possible to predict much more accurately where things were.

One figure I always want to mention as well is Thomas Harrier, who was overlooked, but was the first person to draw an image of the moon through a telescope back in 1689. And we celebrated him, well, back in 2009 now, 14 years ago, when we had the International Year of Astronomy commemorating events like that. And the only reason I mention him is because he was working in West London and not a lot of people know that he lived and worked in Sion House for quite a long time doing that there. So there's this seminal figure in astronomy that is slightly overlooked and and so that renaissance era the european renaissance era that's what 15th 16th century yeah and it's the move from copernicus onwards i think you know copernicus heretically publishing his theory his idea that the sun was at the center of the solar system on his deathbed

or in the year that he died and then it becoming more acceptable to talk about it by the middle of the 17th century it's it's widely accepted and i think that's why kepler sweeps in a little bit and i think kepler is so well known inside astronomy circles but not to the same degree as like newton is outside of astronomy circles so i think everyone always knows newton for sort of you know this writing down the maths of sort of gravity and how you could calculate that but it was kepler that really took those laws and then was like okay so how does that apply to planets and their orbits and then how can we then calculate using that where you know where they're going to be and predict where they're going to be and then that led to people realizing there's something wrong

with mercury's orbit and hey our laws of gravity don't match mercury and then that is obviously einstein's theory of of general relativity as well with gravity so you can see all the little dominoes you know that have to fall when you look back at sort of this history of astronomy especially that this first effort and push to put things down into the into the maths. It's time to get onto our listener questions there've been so many interesting ones so let's see what we get here. So Robert, Jack D. Mayher on Twitter asks, what big astronomical discoveries were more recent than people would expect them to be? Well, Jack, I mean, Beck has already referred to black holes,

which I think is a great example, but my choice I think would probably be exoplanets, planets in orbit around other stars, because despite the canon of science fiction, all the science fiction films that we've had for for decades you would imagine from those that we'd known known for sure about planets around other stars for a long time but actually the first one was only discovered back in 1992 and that was a pretty exotic example of planets going around a pulsar around a neutron

star the remnant of a supernova explosion but But since then, in only the last 30 years, we've discovered more than 5,000, and there are hundreds more candidates waiting to be confirmed. So, you know, you would think from all the conversations, you know, you would imagine, oh, yeah, of course we knew that there were lots of planets around other stars. Of course we know the solar system's not unique. And I think astronomers were almost all certain that was the case,

but it took a very long time to confirm it for sure and now suddenly it seems really really easy you know it's one of those paradigm shifts where you go from oh you know uh it's really hard do we ever know for sure there are plans around other stars to oh yeah there are thousands of them and actually if we look around there are billions and billions we just haven't found them yet for me it's also the growth of the size of that field within the past couple of like decades as well so i started my phd in 2013 so 10 years ago and even back then there was you know there's a few people studying exoplanets but the field wasn't that big whereas now it feels like oh my everybody's doing exoplanets and you can see that reflected in like jdwst proposals as well like 30 percent

of jdwst proposals are for exoplanets and yeah okay it was sort of built with that science goal in mind but like it just shows you like from 95 onwards like it's what i was saying yeah and even from last month when we were talking about the future of observatories how many of the future observatories will also be looking into exoplanets chemical compositions and things like that so yeah it's and that quest for an earth-like a genuinely earth-like planet around another star or something biosignatures or whatever it might be just yeah tantalizingly close you know i mean i made this silly predict i think in about 2000 i thought oh yeah by 2020 we'll definitely know for sure if there are other earth-like planets and well there you go don't make predictions i feel like we have

we've got like the the one that's the most we've got some like earth size we've got the one that's the most earth mass we've got the one that's orbiting the most sun-like star but we haven't got the the venn diagram of all of those three it's almost it's that little bit in the middle of venn diagram that isn't quite okay i'm becky jenny yin wants to know how many different ways did people try and figure out the speed of light? Very many, Ginny, and I hope you'll forgive me for the book plug. But in my book, A Brief History of Black Holes, there's a whole chapter on measuring the speed of light as well. So it's obviously a key idea when you think about black holes as well.

But if we think about sort of the big experiments, you know, you've got Galileo, who I guess is sort of the first recorded written experiment of someone trying to do this with basically two lamps on hilltops and it was sort of people you know revealing their lamp and not revealing the lamp and trying to time when you actually saw like the other person revealing the light from the lamp or not but the two hilltops weren't separated by a great enough amount for human reaction time to be able to record the speed that the light actually arrived at I guess the next person to mention is Ole Roma, who actually did this off the back of something that Galileo was

doing. Galileo was trying to give people a way of determining what longitude you were at, essentially to try and work out time zones with sort of the advent of, you know, the discovery of the new world, people wanting to know, okay, what time is it in, you know, Spain? What time is it in Brazil? That kind of thing. With the motivation being trying to find your longitude, you know, with the advent of a lot more exploration around the world on ships, he realized that you could use a moon of Jupiter, Io. It orbits every 42 hours. That's essentially a clock that you can use to work out, okay, if I know the time here, I can know my time where I am in the world from how much

more delayed Io reappearing behind in front of Jupiter is. I can work out how much of a delay that is and therefore how far around the Earth I am. Of course, he didn't really think about the fact that you're on a moving ship trying to work out when Io is appearing and disappearing. But the bigger problem was that they realized that throughout the like the earth's year like you could try and measure this in summer and winter and there'd be a strange delay to the when you were sort of seeing io reappear from behind jupiter and basically ole roma was like right we gotta figure this out and observed things meticulously and was like okay so in winter compared to in summer there's like a 22 minute delay and that's basically the time it takes light to travel earth's orbit he didn't make that connection he never actually wrote down that that's what it was but it was the measurements that then christian hoygens then used to calculate

a value for the speed of light a couple of years later so this is sort of the end of the 1600s we're talking about now so galileo was sort of more like the early 1600s and then I think the only person we need to mention as well is sort of Hippolyte Fizzo I think that's how you pronounce his name I butcher people's names Robert gently nodded there so I think we'll go with that I love what he did to mention it so he sort of worked on sort of Galileo's principle of like two hilltops right and you have this source of light that's fired in between a wheel that has little tooths. So imagine like a cog or a gear. When you fire the light between one tooth, it reflects off a mirror.

In this case, it was about eight kilometers away. Comes back again. And you can rotate your wheel at a certain speed so that it gets blocked by the next tooth of the wheel. And so if you know the distance between sort of the mirror and the distance the light's traveling and then the speed that you're rotating your wheel at, you can then work out the speed of light. So I think it was a really clever way of doing it.

And obviously they needed, you know, a good distance between the two places of sort of setting off the light and reflecting it back again. But that was in around about 1849 that that was sort of, it was a very accurate measurement as well. It was around that sort of setting off the light and reflecting it back again but that was in around about 1849 that that was sort of it was very accurate measurement as well it was around that sort of you know like 300 000 kilometers per second mark but then after that you then get into sort of okay you've got maxwell's equations now for describing waves of electromagnetic waves and you have other

fundamental constants that you can then use to work out the speed of light from that and so people would tend to sort of devolve into that after that rather than these you know incredible like we must build this giant toothed wheel yeah to do this um or expressing the speed of light based on earth's orbit distance from the sun which again it's you know you can you can express the speed of light in that way but unless you know the distance from the earth to the Sun, it's obviously very difficult to get a speed in everyday units. Yeah. Okay. And Robert Lucy San says,

how extensive was the knowledge of astronomy to the Incas? So the answer is apparently very much so. You know, astronomy was very important to the Incas, and there are researchers like Stephen Goldberg, who works for the International Astronomical Union, along with one of the former vice presidents of the RAS, Steve Miller, on ensuring that astronomy respects indigenous peoples and by that it's things like making sure that you cite observatories in a respectful way and you understand that this is not just land that we should appropriate for this use

but that we have that negotiation and consensus and consent of peoples it affects. And the period of time when the Incas were doing this was from roughly the 13th to the 16th centuries at the time. In the 16th century, obviously, you have the Spanish conquest of South America, Middle America, and, you know, that really destroys that civilization. But we do see phenomenal monuments and temples that remain despite that destruction. But what Stephen's done is explore phenomenal monuments and temples that remain despite that destruction. But what Stephen's done is explore these monuments and structures in Peru. There's quite a lot still there, and they have monuments and temples that are aligned both to the sun and the moon, so they do things like mark the solstices and equinoxes,

like the Neolithic monuments in Europe where you get, say, a shaft of light going into a building at the solstice sunrise and all those kind of wonderful things there's really phenomenal pictures and i absolutely recommend you seek them out he gave a talk to cern a few years ago and there are all these beautiful illustrations of it one of them for example is described as the awakening of the puma at kenko grande in the cusco valley and again in peru and another one has a light tube that lets moonlight in as well to light up the interior and he also describes that they use the Pleiades they looked at the appearance of the

stars and the Pleiades to determine whether it was a good time to plant based on the weather conditions in the sky and they align their view of the sky around the Milky Way and being so far south if you ever go to the southern hemisphere or even just down to the Mediterranean and further south what you realize is you're in the summer at least you're in june i should say because in the southern hemisphere the season is the other way around you would see a much brighter milky way you're looking towards the center of the galaxy it's much more dominant and a lot of the cultures in the southern part of the world base their constellations around the milky way they see as this river running across the sky quite often, including the Incas. And they see the dark clouds, which are genuinely dark clouds of dust in front

of the stars, the Milky Way, the interior of our galaxy, and often make those constellations as well. So in the case of the Incas, they represented a shepherd, a serpent, a bird, a fox, a toad, a llama, and I particularly like an additional baby llama as well. Oh, that's great that is so great like we have the big bear and the little bear they have big llama little exactly yeah and it's stunning i mean you must have been down there did down the southern hemisphere becky it's been many years since i did but you know the milky way is is so dramatic when it's high in the sky like that and becky there's this question here from Natalia Hearn who asks,

I've read that there are ancient rock carvings in Chile that are believed to depict the Magellanic clouds. Do you know anything about this or where they are located? So just to explain, the Magellanic clouds are two irregular dwarf galaxies that you can see in the Southern Hemisphere. So Becky, over to you with the rest. Yeah, they look sort of like nice little fuzzy blobs and other things you can see see from the southern hemisphere um i have sort of heard sort of this before as well like it's been always been the back of my mind that these these petroglyphs these rock carvings in chile where you have these sort of fuzzy blobs the magellanic clouds i looked into this though and i can't find a like a a source that like actually supports. I can find a lot of articles that just state it with no reference,

but nothing like that's in support of it, no images of the actual petroglyphs themselves. So if anybody listening knows anything about this, or maybe we can ask also Sean, the librarian, to dive into anything in the RAS archives as well. Because I think this is actually fascinating that they were recording this time because we could also look at perhaps O'Shaughan the librarians who were to dive into anything in the RAS archives as well because I think this is actually fascinating that they were recording this time because we could also look at perhaps if they've changed as well there is my maybe some argument that there was perhaps a

third that could have turned into what's now known as the Magellan extreme so sort of this idea of them being recorded then might allow you to actually then do this sort of it's like galactic archaeology as sometimes it called as well from these previous observations so if anybody does know anything about this please let us know because we would love to hear about it yeah absolutely so send in any sources that you have or further questions you can email us at podcast.ras.ac.uk tweet at royal astrosoc or find us on instagram it's at supermassive pod so robert what are some of the things that we can see in the night sky this month well it's still you know the height of summer now right you know aren't we enjoying it after that rather chilly spring or at least i certainly am for now so in the summer you know it's very appropriate to continue doing things if you've got the equipment

to do it safely look out for sunspots the The sun is still really active. It's quite exciting to see these huge structures on the surface of the sun. Remember, each sunspot you see is typically sort of about the size of the Earth. So put that in perspective if you do look at them. And those are the things that you can try and look for, given it still doesn't get very dark at night or not for very long. It's looking out for those illuminated noctilucent clouds high in the earth's atmosphere right up in the northern sky yeah i saw some the other day did you yeah i was at a wedding

in cornwall and we were walking back at like you know midnight and it was really dark because we were in the middle of nowhere in cornwall and we just i just looked up and was like noctilucent clouds so yeah exactly you can see them people you can see them even while slightly inebriated after a friend's wedding exactly so there is no barrier so if you're safely walking back from the pub have a look in the northern sky carefully and if you're in a dark enough place they are really beautiful i've only seen them really well once which was uh when common neo wise as well they're very obvious when they're there but better in the north of england and scotland actually if you're listening to this in the uk or further north in the you know in the northern hemisphere it should be fairly easy to spot in terms of stuff you can see when

it's darkish uh venus is still really obvious so if you've been looking west recently i doubt you could have mistaken it's so brilliant in the western sky and after sunset and it's pretty much at its maximum brightness right now if you look at it with the telescope it's an obvious crescent and over the next few weeks and right up towards july it's going to or until the end of july it's going to become a bigger and thinner crescent and to the extent that you'll be able to see that with a pair of binoculars as well it looked like a tiny moon and just gets bigger and bigger gets lower in the sky and then it will pass between the earth and the sun and we obviously won't be able to see it mars is still hanging in there after sunset it's very small to see any detail just worth noting

you can track its progress against the other the background stars and the other planets need a really early start you need to be up well after midnight to or very early in the morning to find them so it's probably better to wait a couple of months longer to see those but in terms of constellations the nights as the nights get a bit longer you start to see more of those summer stars and the milky way is visible one well certainly towards the end of july by midnight you know when the moon's not in the sky that should start to be really obvious stretching up from scorpius and sagittarius the zodiac constellations that are in the direction of the center of the galaxy, and really stunning. And they're packed with stars.

And I often say as well, if you are going south for your holidays, even down to the Mediterranean, southern France, they're that bit higher in the sky and they're that bit more obvious. So just take a small pair of binoculars with you and enjoy the view. But even if you're in the UK, if you've got a good southern horizon, they're really obvious. And we see loads of photos this time of year. People go out and they sit in places. For some reason lot of the time in durdle door indoors it's a particularly popular spot and you see the milky way stretching up from the sea there so you know that's another

nice thing to try well that is perfect timing because i'm literally just about to go on holiday so thank you very much are you going are you going south in italy uh in the heel of italy so take those binoculars. Yes, they'll come in with me. And tweet us with some pictures. I will try. Remember, your phone's just as good for it as usual. Oh, that's true.

Like a little 10 or a 30-second exposure. Well, I do have a little travel telescope. Let's see if Ryanair will let me squeeze that on in my hand luggage. As you know, you can also, there's an app, I think people do now with apps, they actually stack their photos on smartphones. you can even if you if you take a few you might that's probably worth trying as well right well i think that is it for this episode there'll be a bonus in a few weeks and then next time we're traveling to the sun to find out the

latest from the solar orbiter mission yeah i'm really excited for all the interviews gonna have for that one because i really want to know what they're uh they're up to and of course tweet us if you try some astronomy at home it's at royal astrosoc on twitter 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