Thony Christie on Hevelius

Scutum constellation in the Uranographia



Scutum constellation in the Uranographia

Scutum in the Uranographia by Hevelius. Source: Wikipedia.





Would Copernicus have been more convincing if he’d been more accurate?


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.

You can read more about Kepler’s dis­cov­ery of the ellipt­ical path of plan­ets at:
Boccaletti 2001. From the epi­cycles of the Greeks to Keplerʼs ellipse — The break­down of the circle paradigm

Copernicus and the Star that was bigger than the Universe

The constellation Delphinus

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.

Popular belief is that the prob­lem was solved when Galileo picked up his tele­scope and proved the helio­centric the­ory. In fact a recently pub­lished paper by Christopher Graney, The Telescope Against Copernicus: Star Observations by Riccioli Supporting a Geocentric Universe in the Journal for the History of Astronomy shows that the tele­scope could have dealt a ser­i­ous blow to the Copernican model of the uni­verse.
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Planets and Anomalies in the Antikythera Mechanism


This post was chosen as an Editor's Selection for ResearchBlogging.orgMathematicians 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.
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Astronomy in Metal Heaven


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.

Tom Wujec demos the 13th-century astro­labe video from TED.

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.

You can see many astro­labes like the one below at the Museum of the History of Science, Oxford.

A Persian Astrolabe at the Museum for the History of Science at Oxford.


Mysteries and Discoveries of Archaeoastronomy by Giulio Magli


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.
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Are Extraterrestrials a Greek thing?


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.
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