If you have any interest in the history of astronomy you should be following The Renaissance Mathematicus blog and this post, The last great naked eye astronomer, is a perfect example of why. This is a post about Johannes Hevelius who has to be one of the most famous unheard of astronomers ever.
That doesn’t make sense I know. There are a lot of people who haven’t heard of Hevelius, but if you have heard of Hevelius, then the idea that people haven’t heard of him seems nonsense because his work is everywhere in astronomy.
Scutum in the Uranographia by Hevelius. Source: Wikipedia.
Everyone’s happy that most constellations are ancient, but what is less well-known is that not every star was in a constellation. There were gaps between constellations filled with faint and boring stars. These were called αμορφοι amorphoi or unformed stars by the Greeks. This is no good if you want to do science, because things like comets don’t stick to the interesting parts of the sky. That’s why mapping was so important in the Renaissance. In the case of Hevelius, his maps were so useful that he formed seven constellations that stay with us to this day.
I’ll admit constellations like Lacerta or Vulpecula aren’t famous constellations, but he was working with the haps between constellations. The fact that his charts were made of constellations visible in Europe shows he was working in a highly competitive space.
It’s easy to take this kind of work for granted. The output can be seen as an uncontested fact, but Thony’s post put’s Hevelius’s work into the context of its time including the often intense scientific rivalry between astronomer defending personal and national status.
The also shows that while with hindsight it seems obvious that telescopes would bring more accurate measurements, at any given time in history it’s not always obvious that new technology is The Next Big Thing, it could be a distraction or Expensive Dead End.
As a follow-up to yesterday’s post, I was wondering if Copernicus would have been more convincing if he’d used ellipses in his model instead of circles. By using circles Copernicus had to use epicycles like Ptolemy, though not so many. Still, it gave the impression that epicycles were necessary. If that’s the case then why not have a stationary Earth as well? The discovery that planetary motion would be better described by ellipses didn’t come about till Kepler’s work almost a century later. As far as the post title goes, I think Dr* T’s Theory #1 applies here: Any tabloid heading that starts ‘Is this.…’, ‘Could this be…’ etc. can be safely answered ‘No’
So my post title is a bit of a cliché, but the reason I’ve used it is that if the answer is no, then something strange is happening. More accurate is less convincing?
The reason I think that is that Copernicus’ model wasn’t isolated from the rest of thought for that period. It used and built on a number of assumptions of the time. One of those ideas was the creation of the universe by a perfect being. Another was the idea that a circle was a perfect shape, derived from classical geometry. By telling people the Sun was at the centre of the universe and not the Earth, Copernicus was asking people to make a big shift in their thinking. A lot of people thought it nonsense. If he’d made the orbits elliptical as well then many people who would have been willing to listen to Copernicus’ ideas would have balked at that, reducing his potential audience further. In terms of numbers, the population of mathematically minded people who could examine his work was small enough already.
If he’d reduced the number of initial readers further, would his ideas have spread enough for others to pick them 50 years later? It’s impossible to say, but if Copernicus hadn’t given Kepler the idea of a putting the Sun at the centre of universe, could Kepler have discovered it independently? It’s hard to say but, given how Kepler struggled with letting go of circles and using ellipses, I think it’s unlikely.
This is why I’m wary of histories of science that are purely about who got it right and who got it wrong. Copernicus’ use of circles isn’t ‘right’, but it was necessary at the time.
I’ve «cough» borrowed the portrait of Copernicus from Prof Reike’s page on Copernicus. It’s well worth visiting if you want to find out more about the astronomer.
I’ve been trying to watch Cosmos by Carl Sagan. I’ve never seen it and it’s proving to be a bit of a struggle. He definitely can write. Some of the sequences are fantastic, but some of it is badly dated. The thing that really grates to me is his dismissal of Ptolemy and his geocentric universe. For Sagan at best Ptolemy’s system held back astronomy by 1,500 years. At worst he’s only worth mentioning to say he’s dead wrong, like in the first episode.
It’s not really fair to lay into Sagan for his attitude to Ptolemy. His work is a product of its time and it was written over thirty years ago. But the idea that Ptolemy was clearly wrong seems to the popular understanding of Renaissance astronomy. The question here is Why did some people oppose the heliocentric theory of the universe? not Who in their right mind would accept it? It overlooks the power of the Ptolemaic system. If you followed Ptolemy’s work you could predict where the planets would be with enough accuracy for naked-eye astronomy. If Copernicus had only used simple circles, then his model might have seemed better, but he too needed to add epicycles and fudges to make his system match the observable sky. It needed fewer epicycles, but it was hardly perfect.
Mathematicians have a concept, Omega, that is defined as something so huge that any attempt to define it actually defines something smaller. In a similar vein I reckon that any attempt to describe the ingenuity of the Antikythera Mechanism actually ends up describing something less ingenious instead. More research on the device has been published recently in the Journal for the History of Astronomy. I realise that people might be dropping on to this entry from a search engine, without having read any of the earlier posts, here’s a quick recap of what the mechanism is. Continue reading →
Astrolabes at the Museum for the History of Science at Oxford.
If you ever want to embarrass me, try to get me to enthuse about a display of astrolabes. They’re the kind of thing I should love. They’re devices for showing what is visible in the sky at any given time. They’re very similar to the planispheres that people use today. The mathematics behind them is elegant. The best also tend to have extraordinarily ornate metalwork to complement the sophistication of the devices. Yet, when they’re hanging up like this, they leave me cold.
I think the reason is that an astrolabe on display is a dead astrolabe. There are better ways to show a static night sky. What you need is an astrolabe in motion to appreciate them. That’s what makes this talk by Tom Wujec so good. He demonstrates how you could use an astrolabe to tell the time. In his hands, an astrolabe becomes a lot more interesting.
It’s easy to underestimate how much you can do if you’re willing to observe intently. What I also like about this talk is that Tom Wujec emphasises the importance of connecting with the night sky. You could claim accurate clocks have broken this connection, but I’m not sure that’s the case. Where I live light pollution is often so bad that I could not use an astrolabe. He’s right to point out that you can lose things with progress. Ironically Global Astronomy Month with try to show how immense the universe is, while artefacts like this show that on a day-to-day basis for urban dwellers the visible world is much smaller than the cosmos of the past.
Note: Giulio Magli was one of the examiners of my thesis, so his book is hardly likely to get a bad review.
This review rounds off a trilogy to go with Skywatchers, Shamans and Kings and People and the Sky. Like the other two books this could be said to be part of a World Archaeoastronomy approach, but Giulio Magli adds a twist. Some of this is down to the approach he’s taken to archaeoastronomical sites, but he also adds a bit more.
Magli’s approach is similar to what I would have done if I was writing an introduction to archaeoastronomy book. He tackles the sites around the world. So take a deep breath because in his opening section of twelve chapters — slightly over half the book — he covers. Palaeolithic Europe, Prehistoric Britain, the temples of Malta, Egypt, Babylon, East North America with the Hopewell and Cahokia, West North America with Chaco and the Anasazi, Northern Mexico and Tenochtitlan, The rest of Mesoamerica and Palenque, The Incas, Nazca and Polynesia. That leaves massive holes where you would expect to find India, China, Korea and Japan and a lack of African material. That’s more due to the state of play in academic archaeoastronomy at the moment than a fault of Magli. In general Africa has been greatly overlooked and there’s not a lot of integration between Asian astronomy and the rest of the world. It’s getting better, but it’s still under-represented compared to the Mayans and Prehistoric Europe.
If this had been the sum total of the book I wouldn’t be that enthusiastic about it. It’s not bad. It’s written from an astronomical point of view with some amusing digs against archaeologists. If you were interested in archaeoastronomy and approaching it from astronomy and not anthropology I’d recommend this over Aveni or Krupp’s book as an introduction to the field. What really marks out the book as worth reading is section 2. Continue reading →
I had a slight worry earlier today. I have an idea that I think has cross-over relevance between SETI and Ancient History about ancient speculations on extraterrestrial life. I was slightly alarmed when I read Jean Schneider’s new pre-print on arXiv, The Extraterrestrial Life debate in different cultures. In it Schneider argues that arguments about life on other worlds can be traced back to ancient Greece. It sounds like an idea I’ve been kicking around for a couple of months. It was a topic raised by the atomists like Democritus and Leucippus who said that in an infinite cosmos with an infinite number of atoms there must be infinite worlds. Plato rejected this idea, as did Aristotle who argued for a hierarchical cosmos. Schneider says debates in other cultures are derived from this and then asks why it should be only the Greeks who speculated on offworld life. Continue reading →
The slide on the 1980s probes is intentionally blank, because there were hardly any probes sent in the 1980s to Mars. The reason is that the competition between the major powers has moved to Earth Orbit, with the USA building the Shuttle and the USSR building long-term space stations. Recent events have highlighted a couple of reasons why it’s worth looking at this again. One is the registration of lunar heritage by California, which is grabbing headlines for something that Alice Gorman and Beth O’Leary have been saying for a while. The other is Obama’s cancellation of the return to the Moon.
It could be a scientific re-prioritisation, but like the Mars gap in the 1980s, it could also be due to politics. The Nobel laureate already has wars in Iraq and Afghanistan to manage, and he wants to keep his options open for a war with Iran. That could turn very nasty as Iran is next door to his two other problems. It’s possible that there simply isn’t a threat on the Moon, but there is in the Middle East. Unless China develops lunar ambitions, the discovery of water on the Moon could be a scientific curiosity rather than a stepping stone to colonisation.
There’s a few reasons why I don’t like this presentation as it stands. I think the biggest problem is that one of the big factors for making it was that I needed a presentation. It wasn’t an idea that was ready, and to some extent the problem was “there’s something archaeology could say about this, but what?” Now I’m thinking about the social, political and economic effects of Mars exploration. This time around I see archaeology as a tool to finding out about these factors, rather than ‘being archaeological’ as the purpose of project.
Wladimir Lyra’s following in the footsteps of Jack in his arXiv paper Naming the extrasolar planets. Currently planets are tagged after their parent star, so if we found a planet around α Ceti, it would be called α Ceti b. The b in lower case is used for the first planet to be found, c for the second and so on. a is not used to avoid confusing a planet with a star. Unfortunately in the case of some double stars a capital B would be used for the second star, so names could get confusing. So why not name the planets? Lyra gives a couple of reasons why he thinks this would be a good idea. One is that names like Bacchus are more beautiful than names like HD 128311. One person’s beauty is another person’s mess, so I’m not convinced by this. However, he also proposes that names for extrasolar planets aren’t just decorative, there’s also the Copernican principle.
“Mercury — Venus — Earth — Mars is a sequence of equals. Sol b — Sol c — Earth — Sol d would implicitly imply that the Earth is special in some way.” For this reason, Lyra argues that naming the extrasolar planets is necessary to avoid the impression that the Solar system is special. I’m more persuaded by this, but it misses an obvious point — the Solar system is special. It’s where I am, it’s where all humans are and it’s where they’ll be for the foreseeable future.
My biggest objection to his paper was that I’m not sure how helpful it would be. Even dealing with ancient historians I tend to avoid classical names for stars, except in a few cases. Vindemiatrix or Protrygetor, names for the same star in Latin or Greek aren’t as helpful as ε Virginis, because ε Virginis gives the reader a clue as to where in the sky they’ll find the star. Similarly I can see why Lyra would give the name Bellerophon to a planet, but I wouldn’t find it as helpful as 51 Pegasi b. The IAU have said there are likely to be too many extra-solar planets to name. The problem isn’t likely to be the supply of names, which is a shame as Lyra solves that neatly. It’s memorising what goes where.
For that reason I’d prefer a Bayer style system so in the ε Eridani system you could number the planets from innermost orbit to outer I, II, III and so on. It sounds simple, but it won’t work. The first star you find in a system is likely to be the most massive, not the closest to the star. Using this system you wouldn’t be able to number planets until you discovered every planet in the system. Every time you discovered a new planet you’d have to renumber the system, causing havoc when you try and use older papers for comparison which use a different numbering, or else have a database of each system’s number order for planets. Another solution would be to number planets in order of mass, but that’s not likely to be fool-proof either.
Another possibility would be a Bayer style designation which embedded information about a planet in its name. So Gliese 876 d would be Gliese 876 p1.9379, p for planet and the number following it is the orbital period. This too has flaws though as orbital periods can be calculated from assumed masses and may be revised in the future. A possible solution would be to only give names to the minimum number of significant figures necessary. In the Gliese 876 system that would give planets names p60 for b, p30 for c and p2 for d. The exact figures may change, but the relative order of periods would mean you would have a fair chance of identifying a planet named in a early paper on the system at some time in the future.
Things do change and catastrophes occur upsetting systems. Hybrid names like 55 Cancri p 5000 Argive might help track references to 55 Cancri d as papers accrue over the years. I’ll cheerfully concede a name like Althaea for planet 16 Cygni Bb (the first star discovered orbiting 16 Cygni B, hence the Bb) would be easier to understand. Ultimately though I think the problem is not the names, or their allocation. It’s what the names are used for.
The visible planets had names because they were visible, distinctive and needed names. Uranus and Neptune also got names because there were so few planets so more names were not mentally taxing. Lyra points out that asteroids have names. This is true, but when 1 Ceres and 2 Pallas were discovered it wasn’t anticipated that 2309 Mr Spock would be joining them. These days a catalogue number is essential to identify an asteroid, the name is not so important. The same can be said of comets. Originally they were named by the date they appeared. After the discovery of the periodicity of comets by Halley, they began to be named, but these days comets also bear catalogue numbers. So who will use these planet names?
A name for something that carries information about it. e.g. An example Stewart and Cohen give is if you know what an arrow and a head are, you can work out what an arrowhead is, even if you haven’t come across that word before.
For the vast majority of the extrasolar planets their existence will only be noted by astronomers, much like stars and galaxies today. While names may be beautiful, astronomers don’t seem to use them for stars, nore for many galaxies. Likewise names may add something of value to extrasolar planets, but equally use of them on a regular basis could be cumbersome. Names have most value where things are not easily categorised, like the rocks on Mars. Mythological names have the further disadvantage in that they are purely abstract rather than ontic dumps. An ontic dump would have the double use of not only labelling a planet, but giving some information about it. Bayer classifications, when used as names, are usually ontic dumps, as are the current extrasolar planet names. This matters in the Lyra name system as some of the names actually run counter to Graeco-Roman cosmology.
As an example the name Dike is associated with a planet found in Libra. In classical mythology Dike, Justice, is in fact an aspect of Virgo. Libra was originally the Claws of Scorpio. Once the method is explained then the Lyra system makes sense, but it would be counter-intuitive in some cases for anyone with a knowledge of classical mythology. Another example would be that Amphitrite, the nymph wooed by Poseidon with the aid of Delphinus is not associated with constellation Delphinus. If names are to be used then a method divorced from the mythologically laden meanings of the modern constellations might prevent confusion. That’s why I think Stuart’s suggestion to use names from all sorts of literature has a lot of merit. Though there’s something to be said for Exoplanetology’s suggestion too.
Ultimately the names for the extrasolar planets will be names that have meaning to the community of regular users. In the past classical references were common culture shared by academics in all European universities. Those days have gone. I could bemoan the decline in classics, after all I’m an ancient historian. But there’s also a lot to celebrate about the creation of academic links outside the Euro-American community. If names are adopted hopefully they’ll reflect that it’s not just the number of worlds that has grown, but also the astronomical community from a small élite at the start of the 20th century to the worldwide exchange of information and ideas that we have today.
Some posts take quite a while to write. This is a response to Candy Minx and Martin Rundkvist who were discussing the Antikythera Mechanism back in 2006 (Antikythera, Time, A Reply to the Minx). Candy Minx thought that the Antikythera Mechanism was an expression of what was already known and embedded in a society through things like myth and ritual. Martin thought that the mechanism was far more complex, indeed needlessly complex, for an ancient society and so was something quite different to the folk astronomy of the time. Originally I planned to write a fence-sitting compromise. I thought that Candy Minx was right to an extent, there was no need for a device like this because rituals and folk observation could allow people to time the year as well as they needed. At the same time I thought that Martin was right to point out that the mechanism gave results with far more accuracy than folk astronomy needed, or would even recognise. A different sort of astronomy is visible in the Antikythera Mechanism. I didn’t blog too much about the 2006 paper because I attended a few of Mike Edmunds’ talks on the topic and heard that more would be published, which happened in 2008. Anyhow in my own fluffy and fence-sitting way I’ll now offer my compromise.
Someone with an extraordinary imagination built the Antikythera Mechanism and, if he were alive today, we wouldn’t hesitate to call him a scientist. I don’t know if the designer was in the same league as Newton or Galileo, but he was certainly the equal of Kepler, Copernicus or Brahe. It’s hard to overstate how extraordinary the device described in the 2006 paper is, but I’m going to give it a go.
If you’re the one person who hasn’t heard of the Antikythera Mechanism then Nature have a handy video introduction.
All that remains now is a collection of corroded lumps found off the island of Antikythera. The 2006 paper described what the team discovered after x-raying the lumps to read the hidden inscriptions without prizing apart the device and damaging it. Prior to this paper it was thought that the device could keep track of the Sun and the Moon. This is no small feat.
Epicycle et deferent. Image by
The Sun would be moving slowly against the background stars, so over the course of a year it would pass through all the signs of the zodiac. The Moon however is more complex. The Moon also moves in front of the background stars, but it only takes about 27 days to do this. It’s called the sidereal period. So you need a couple of gears to drive those two motions. But you wouldn’t really think of the sidereal period as a month. For most people the synodic period, the time between one New Moon and the next or the time between one Full Moon and the next, is a month. This is around 29½ days. Throw in extra gears for driving other displays showing eclipse cycles and it’s clearly a complex device. The original studies found evidence of epicycles, gears mounted on other gears. Add other features like displays for eclipse and lunar cycles on the back and it’s obvious you have a complicated device. The 2006 research showed that in fact it was all a bit more complicated than that.
The Moon’s movement isn’t constant. It speeds up and slows down. This is because its orbit isn’t exactly circular. Instead it’s slightly egg-shaped. The point furthest from the earth is the apogee and the point closest to the Earth is the perigee. When it’s near the apogee it travels slowly, but when it moves closer to the Earth it picks up speed until it passes perigee and then it slows down again. This is called the first lunar anomaly. The difference is noticeable by the naked eye, if you’re willing to make systematic observations. This is all simply explained by Kepler’s Laws of Planetary Motion. There’s small problem. Kepler used ellipses.
You can’t use elliptical gears. The point of gears is that they must have intermeshing teeth. An elliptical gear would lose contact with the driving gear as its axis changed. Instead it seems that the mechanism used two gears, one slightly off-axis from the other. The rotation was connected by a pin-and-slot arrangement, so that the one gear wouldn’t turn at quite the same rate as the other gear. The on-axis gear can then be turned reliably by the drive gears, while the motion of the moon can driven by the off-axis gear. So you have a device that can track the sidereal, synodic and anomalistic months, all while the Earth is spinning round the Sun. If that’s causing your head to spin you might want to skip the next paragraph.
There’s another problem. The lunar anomaly describes the Moon’s travel from one apogee to the next. This apogee is also rotating around the earth. If the apogee is in Aries then two and a bit years later it will be in Cancer, and another two and a bit years to move into Libra until it too has travelled through the zodiac over about nine years. So now we have a device which tracks the Moon around the Earth, and its phases and it’s variable speed and variations in that variability, while also keeping track of the Sun’s position, potential lunar and solar eclipses and intercalation cycles so you know when to stick an extra month in to keep the lunar months in step with the solar year round gears, some mounted slightly off axis to create a pseudo-sinusoidal variation using circular gears to replace ellipses. If you have funny feeling near the back of your head right now, that’s probably your brain trying to crawl out of your ears. The Antikythera Mechanism is insanely complex. Still just because it’s insanely complex, that doesn’t make it scientific.
In fact you can argue about whether or not Science existed in the ancient world. Certainly a lot of elements like testing ideas with experiments didn’t really become popular till after Galileo. On the other hand some natural philosophy of the time was based on observation. There was certainly technology which was the result of applied knowledge. With those kind of provisos a lot of ancient historians would be happy with the idea of ancient science, albeit a science different to post-Renaissance science. In this case, the sheer intense observation and calculation involved in making the Antikythera Mechanism marks it out as a work of ancient science. There’s also another factor which might make it more scientific than artistic.
To some extent the Antikythera Mechanism Research Project have been interested in hanging a name on the device. It was thought to have originated in Rhodes and sunk on its way to Rome, which would have connected it to the home city of Hipparchus, one of the great astronomers of antiquity. The 2008 paper has examined the parapegma on the mechanism and discovered it may be connected to Syracuse, home of Archimedes.
A parapegma is a calendar, usually with holes for sticking a peg into for marking the days. In the case of ancient Greece they’re interesting when they tell you what day of the month it is, because each Greek city had its own set of months. The months were usually named after religious festivals, and this was tied into local politics. That meant having your own calendar was a good way of showing your independence. The best match for the months mentioned on the mechanism is Tauromenion, modern Taormina, in Sicily. This is likely to have shared some months with Syracuse as it was re-settled from there in the fourth-century BC, so Syracuse is a strong possibility for the home of this device. Archimedes is said to have invented a planetarium according to Cicero and is thought to have written a lost book on astronomical devices. However he could not have made this device. Archimedes died in 212 BC. The Antikythera Mechanism is currently thought to date to the second half of the second century BC, but that might change. But it was very likely to have been made after Archimedes death and that’s what makes it scientific.
Art can be collaborative, or it can be personal. Science in contrast is built on cumulative knowledge. The person who invented the gearing did not have to be the person who made the astronomical observations. He didn’t even need to live in the same century as the astronomer. In fact the maker of this device might not have done either. He could have followed a kit and added his own personal touches on the casing. There’s a core to this device which, once expressed, is independent of personal vision. Archimedes didn’t have his own personal Moon which moved in a different way to everyone else’s, while an artist can have a personal interpretation of the Moon.
A reason people might think the Antikythera Mechanism is a work of art is that it’s clearly the result of a lot of imagination. Great art requires imagination, but so too does great science. It requires the kind of imagination that can look at a toolbox full of circles and see ellipses. The kind of imagination that can watch wheels turn within wheels as bodies waltz to the music of the celestial spheres. Another common factor between art and science is that great art can show a new way of looking at the world, and great science does this too. That’s why I disagree with Candy Minx when she says “Science is always playing catch up with the poets.” Science can reveal beauty too, as a visit to the Antikythera Mechanism Research Group’s homepage would show.
Freeth, T., Bitsakis, Y., Moussas, X., Seiradakis, J., Tselikas, A., Mangou, H., Zafeiropoulou, M., Hadland, R., Bate, D., Ramsey, A., Allen, M., Crawley, A., Hockley, P., Malzbender, T., Gelb, D., Ambrisco, W., & Edmunds, M. (2006). Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism Nature, 444 (7119), 587–591 DOI: 10.1038/nature05357
Freeth, T., Jones, A., Steele, J., & Bitsakis, Y. (2008). Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism Nature, 454 (7204), 614–617 DOI: 10.1038/nature07130