Astronomy at Ston̈ehen̈ge for the 2010 Summer Solstice


I’ve been busy, recently and I’m likely to stay that way for a while, hence the lack of posts. Still, I’m hop­ing to be able to take a trip to Stonehenge this year to see the sol­stice. That’s why my pre­dic­tion is that it will be cold and wet and thick cloud will pre­vent any­thing inter­est­ing mak­ing an appear­ance. However, if there are clear skies, there could be plenty to see over Stonehenge this sol­stice.

Natural Astronomy

There’ll be plenty to see in the even­ing sky after sun­set at 9.26pm. To the west Venus will be extremely bright at mag­nitude –4.0 (the lower the num­ber the brighter some­thing is). When you see it you won’t be able to mis­take it for any­thing else. That will be set­ting at a quarter to mid­night, so there’ll be plenty of time to see it.

Stonehenge astronomical chart for sunset solstice 2010

Position of the plan­ets at sun­set. Click for full size.

Moving to the left, are Mars, Saturn and the Moon. Mars will be mag­nitude 1.3 so it won’t be the bright­est thing in the sky, Arcturus and Vega will be brighter but it’ll still be easy to find. If you’re strug­gling find the Plough. The two pointer stars that point up to the Pole Star will be more or less also point­ing down to Mars this even­ing. Mars sets at a quarter to one, but if you want to see it real­ist­ic­ally you’ll have to be look­ing before mid­night. If you’re lucky it’ll have a slight ruddy glow. Saturn will be the only bright object between Mars and the Moon. In fact it’ll be slightly brighter than Mars in per­fect atmo­spheric con­di­tions, but I doubt my eyes will be good enough to meas­ure that.

The Moon will be in Virgo, near the star Spica, which was thought to be a sheaf of corn in the hand of Ceres, if you’re Roman, or Demeter, if you’re Greek. Fans of myth­o­logy will be keenly aware that Demeter/Ceres had a daugh­ter with Zeus which makes her not tech­nic­ally a vir­gin, but the Greeks called her Parthenos and that usu­ally gets trans­lated as vir­gin. To find Spica usu­ally you’d fol­low the arc of the handle of the Plough to Arcturus, and then Spica is the next bright star down. This night it’ll be the closest bright star to the Moon. It could be hard to spot because the Moon will be bright. It’ll be 69% lit, nine days old and wax­ing gib­bous. It’ll be more or less low in the sky to the south at sun­set and set around 1am, which is astro­nom­ical mid­night. It’s not the same as civil mid­night because these days Stonehenge is on Daylight Saving Time, like the rest of the UK.

Stonehenge astronomical chart for midnight solstice 2010

Stars at 1am over Stonehenge. Click for full size.

Around 1.20am Jupiter rises. It’s likely that you’ll need to wait till 2am to get a good view. It’ll be shin­ing in sil­ver at mag­nitude –2.4 and, because Venus will have set, it’ll be the bright­est planet on the sky. Jupiter will have a part­ner, but it’s highly unlikely you’ll see it at Stonehenge. Uranus will be close to Jupiter. If you hold out your hand at arm’s length then Uranus will be five or six little fin­ger­nail widths to the right of Jupiter. Normally there’s no chance at all of see­ing Uranus, but at the moment it’s at mag­nitude 5.8 which puts it right on the limit of human vis­ion. If you have very good eye­sight and the atmo­spheric con­di­tions are per­fect you’ll see what looks like a very faint star next to Jupiter, and that’s Uranus. But even if we have that, I still doubt you’ll see it.

The reason is that it takes time for your eyes to adapt to the dark. Ian Musgrave says it takes a few minutes to see down to mag­nitude 5 or 6. Your eyes need to build up chem­ic­als to make them more sens­it­ive. Every time you see a bright light, like car head­lights from the nearby roads, torches from other vis­it­ors who — quite reas­on­ably — don’t want to break their necks walk­ing around and any light­ing from English Heritage this adapt­a­tion will be lost. On top of this there’s light pol­lu­tion. We don’t just use energy light­ing streets. A lot of energy is used to light up the sky, for no obvi­ous reason. This reflects from any water droplets in the atmo­sphere and gives a sodium glow to the sky. Even cit­ies over the hori­zon will be vis­ible by their light pol­lu­tion and this will pre­vent you from see­ing some of the stars. You’ll stand a bet­ter chance of see­ing Uranus if you use binoculars.

There is another difficult-to-spot object in the sky. To the north near Capella is Comet McNaught. Searching on the web for this is no help. There’s a lot of Comet McNaughts because Robert McNaught has found over fifty of them. This one is Comet McNaught 2009 R1. The cur­rent fig­ures I have are that it will be between mag­nitudes 5 and 6. If that’s the case then you might not see much without dark-adapted eyes and it’s a bin­ocu­lar object. This fig­ure is uncer­tain though because the comet is get­ting closer to the Sun. Around June 30-ish it’s pre­dicted to be as bright as mag­nitude 2. Capella is not too hard to find. It’s the only bright star above the north­ern hori­zon, and it will be due north around half-past mid­night. The comet will be a couple of degrees above it. Look for a fuzzy star.

The Sun is due to return a few seconds before 4.52am. Again, day­light sav­ing explains why the Sun sets less than three hours before mid­night, but doesn’t rise till almost five hours after.


Or, if you don’t tell your friends what they are, UFOs.

The big events will be the passes of the International Space Station. There’ll be two and half over Stonehenge. The first will be at 1.08am till 1.10am. You’ll be able to see the ISS drop­ping from 38º up in the sky to the south­east down to the hori­zon. It’ll be bright (mag­nitude –2.7) but it will also be fast. This is the half appear­ance and you may not see it. You best chance is to be look­ing at Aquila, the bright­est star in the south­east at this time, and it should appear near there.

The next appear­ance is the best. At 2.40am it will rise in the west and pass over­head before set­ting in the east at 2.46am. It will look like Venus did, but it will vis­ibly be mov­ing across the sky. It could look like an aero­plane and if any­one else says that you might want to agree before point­ing out that there’s no vis­ible flash­ing lights like there would be on an aero­plane. It will also be trav­el­ling too fast. Get your friends to rule out other obvi­ous causes like Chinese lan­terns, reflec­tions of head­lights, plan­ets and so on so that you sound like you’ve been reluct­antly con­vinced that whatever you saw was not of this world.

Then at 4.15am you can make every­one jump out of their skin by yelling “They’re BACK!” when the ISS makes another pass from the west again. This time it will set 4.23am in the eastsoutheast.

For extra UFO points you can also try point­ing out an Iridium flare. This is a sud­den bright reflec­tion from one of the Iridium com­mu­nic­a­tions satel­lites. There are two dur­ing the course of the night. At 10.52:44pm on June 20 there’s a mag­nitude –1 flare west­north­w­est above a hand­span above the hori­zon. At 3.22:06am there’s a brighter mag­nitude –4 flare in the east­south­east. These will be fast; they’ll last for just a few seconds.

Flare Simulation. Source: Wikimedia Commons

Heavens Above, where I got these details from for the ISS and Iridium also has some transit times for fainter satel­lites, but the night sky is littered with satel­lites. If you see any­thing that looks star-like mov­ing across the sky over six-eight minutes then it’s quite pos­sibly a satel­lite. Some of these could be mis­taken for aero­planes. Registering on the site will enable you to print off your own star charts for ISS and satel­lite passes. If you’re on twit­ter @twisst can tell you when the ISS is passing over your loc­a­tion and send you alerts.

If you’re inter­ested in vis­it­ing Stonehenge for the sol­stice this year and want more prac­tical advice, like remem­ber­ing to pack toi­let roll, you’ll find Heritage Key help­ful. And if there are clouds, it might not all be bad news.

Explore the Lunar Surface with MoonZoo


The Zooniverse, the people behind GalaxyZoo has released its latest pro­ject, MoonZoo. They’re ask­ing the pub­lic to help them map craters on the sur­face of the Moon using new images from the Lunar Reconnaissance Orbiter. The inter­face is simple and nifty as they show below.

I liked the idea of GalaxyZoo. It’s pro­duced sev­eral papers already so it’s clearly a pro­duct­ive tool as well as a great way for the pub­lic to get involved. The real­ity was slightly dif­fer­ent for me as I was never sure I was doing it right. That shouldn’t be a prob­lem, the sig­nal comes from many people check­ing the same pho­tos rather than just one per­son. Still, when I saw an example photo of a spiral galaxy, and I couldn’t see the spiral, I decided I was prob­ably con­trib­ut­ing more noise than sig­nal. What I like about MoonZoo is the guide at the bot­tom show­ing what the light­ing does to the image. I can see images where I’ve no idea if the things I’m look­ing at are craters or hills. The guide at the bot­tom resolves that prob­lem and then tar­get­ting craters becomes simple. My res­ults won’t be per­fect, I’ve not got an eye for boulders, but I can see how even by pos­i­tion­ing crater mark­ers I can help con­trib­ute to the accur­acy of the project.

It’s not some­thing I’d want to do for hours on end, but as a way to clear the mind in a few minutes or wind down at the end of the day it’s fun and it helps someone else.

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.

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

Theorising Space Archaeology


The future archae­olo­gical site of Spaceport America. Photo (cc) Jared Tarbell

There’s a thought-provoking post on Space Archaeology about how you define the term Space Archaeology. I’ve gen­er­ally just thought of it as the archae­ology of remains asso­ci­ated with space­flight, but I’ve never seen the need to give the defin­i­tion any ser­i­ous thought. It’s a small enough field as it is without draw­ing up bound­ar­ies. Steve Wilson (I assume, the blog is uncred­ited) has given it more thought, and he’s come up with a much more inter­est­ing way of look­ing at it. He sees Space Archaeology as being made up from Aerospace Archaeology (the bit I was think­ing about), Xenoarchaeology (the mater­ial remains of alien civil­isa­tions) and Exoarchaeology (any mater­ial remains that are offworld).

My first reac­tion was does this add any­thing? Adding in Xenoarchaeology is awk­ward as there are no known alien arte­facts. There’s crank mater­ial of ancient astro­nauts and vari­ous forms of SETI which are anthro­po­lo­gical con­cerns and not spe­cific­ally archae­olo­gical. Adding Exoarchaeology only adds fic­tional mater­ial. Things like the archae­ology of ter­ra­form­ing would fit in this cat­egory. As it stands it only adds an archae­ology of things that don’t exist. The dia­gram also excludes Space Heritage and Space Junk, which do exist. As a defin­i­tion, I’m don’t think it helps. However as an ana­lyt­ical tool, I think it could be very clever.

I’ll start with Xenoarchaeology, because that’s the field that’s easi­est to dis­miss as barmy. What’s the evid­ence of palaeo­con­tact? There isn’t any really. But think­ing about how people do Xenoarchaeology, and what would be neces­sary to show the pres­ence of alien mater­ial on earth could be use­ful. Tools developed in this area can then be applied to ‘crash sites’ like Roswell in the dia­gram where Xenoarchaeology and Aerospace Archaeology inter­sect. You won’t learn any­thing about alien civil­isa­tions by study­ing Roswell, but you could learn about how humans react to per­ceived alien vis­it­a­tion. Such research could have helped at Carancas. Likewise a ser­i­ous study of how xenoar­chae­ology is prac­ticed could give genu­inely use­ful insights into the assump­tions in SETI programmes.

Similarly Exoarchaeology poses its own prob­lems when look­ing at inac­cess­ib­il­ity. Thinking about these issues could high­light how the archae­ology of space­flight in orbital space makes demands and chal­lenges that we simply don’t have on the ground. Thinking about it this way Space Heritage and Space Junk could straddle every zone between Exoarchaeology and Space Archaeology. It depends on whether you class the human waste mat­ter on the Moon as part of Aerospace Archaeology or not. I’d include Space Junk / Exogarbology too, because a lot of ter­restrial archae­ology is the study of junk.

While Space Archaeologists might not need bound­ar­ies, draw­ing up defin­i­tions can high­light what makes a field inter­est­ing and also throw some basic assump­tions that need ques­tion­ing. The one that both­ers me is the idea of Xenoarchaeology.

Oddly, it’s not the Xeno bit. I could be pedantic and say archae­ology is the study of the human past through mater­ial remains. Still, the stick­ing with human is a throw­back to the early nine­teenth cen­tury when Man (prefer­ably with a mous­tache and stovepipe hat) was a cre­ation apart from the anim­als. Early palaeo­lithic archae­ology, palae­on­to­logy and prim­ato­logy are sim­ilar enough that it’s look­ing more and more like an arbit­rary dis­tinc­tion about where human ends. It’s the archae­ology bit that troubles me. The study through mater­ial remains when, so far as is known, there are no known mater­ial remains of extra-terrestrial activ­ity near Earth. I think study­ing the human reac­tion to pro­posed alien inter­ven­tions is an inter­est­ing research prob­lem. We study ancient faiths, so why not study mod­ern faiths too? It’s just that archae­ology isn’t always the best way of doing it. Sometimes a bet­ter approach is anthropology.

Thinking about Space Anthropology could have two advant­ages. One is that it recog­nises the inter­est­ing work done by eth­no­graph­ers. Alice Gorman has poin­ted out that indi­gen­ous peoples have a rough enough time as it is get­ting any recog­ni­tion in their sac­ri­fices for space explor­a­tion. Taking American-style four-field anthro­po­logy as a model also points to some other inter­est­ing research top­ics. For example is there any­thing bio­anthro­po­logy could con­trib­ute, and how do bio­anthro­po­lo­gical con­cerns integ­rate with research that is already being done?

I real­ise that by now my response is a bit longer than the ori­ginal post, which was flag­ging up an idea and not inten­ded as a fully formed model of Space Archaeology. Even so I think it’s an inter­est­ing way of think­ing about what archae­olo­gists of space explor­a­tion do. I’d love to see it developed further.

Monkey business on Mars reveals something nifty


I went to Skeptics in the Pub last week at Nottingham to hear a talk by Doug Ellison on the explor­a­tion of Mars. One of the sub­jects that came up was the Gorilla. The Sun recently repor­ted that a Mars rover had found evid­ence of a Silverback gor­illa while ram­bling across the dusty and arid plains of Mars. ‘Enthusiast Nigel Cooper — who has stud­ied thou­sands of pho­tos taken by Nasa rovers and pos­ted online — said: “It’s def­in­itely a creature of some sort.“

I’m rub­bish at debunk­ing this kind of thing. Basically I get as far as a lack of bana­nas and rain forest before yawn­ing. If someone ser­i­ously thinks that the gov­ern­ments of the world are con­spir­ing to hide the exist­ence of a lone, and pre­sum­ably very hungry, gor­illa then they have more urgent prob­lems than a lack of basic bio­logy or geo­logy. What is it that makes a global con­spir­acy to hide evid­ence of an advanced civil­isa­tion on Mars, with pyr­am­ids, faces and anom­al­ous gor­il­las plaus­ible? Unambiguous evid­ence of life on Mars would be a key to the vaults of any gov­ern­ment with a space pro­gramme, so why would sci­ent­ists hide that? You’re not going to answer that ques­tion by con­firm­ing that what we have is a rock. Still, that’s what Doug Ellison did with the video below. What makes it worth watch­ing isn’t the con­clu­sion but how he got there.

The tool he used in the video is the Midnight Mars Browser, which you can down­load on Windows or Mac for free. I didn’t know about this. It’s a tool that takes the pho­tos from Spirit and Opportunity and dis­plays them as vir­tual pan­or­a­mas. You can fol­low in the tracks of your favour­ite rover. The gor­illa might be dull, it’s a rock, but the tool for examin­ing it looks bril­liant. This is why the talk was so com­pel­ling. There’s masses of inform­a­tion about Mars you can access. You can even fol­low the (delayed) blog of a Mars rover driver at Mars and Me if you want the back­seat driver experience.

It’s an example of debunk­ing done well. I doubt that he’ll have con­ver­ted any die-hards, because simply examin­ing the evid­ence isn’t going to address their under­ly­ing prob­lems. For every­one else he’s not only shown that it’s a not a gor­illa, he’s also shown the way to more inter­est­ing places that can take our under­stand­ing of Mars fur­ther. The rest of the talk showed sim­ilar insights into the equip­ment on Mars and how you can use the data com­ing from there. As for the rest of the solar sys­tem, he runs a forum where you can find out more at unmanned​space​flight​.com.

It’s not just Jack who names the planets

Gliese 667c. Connected to, but definitely not, Ganymede in Lyra's naming system. Photo (c) Nasa.

An artist’s impres­sion of Gliese 667c. Connected to, but def­in­itely not, Ganymede in Lyra’s nam­ing sys­tem. Photo © Nasa.

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?

Ontic dump:

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.

If you’re won­der­ing who Jack is, there a video on YouTube.

The Antikythera Mechanism: Art or Science?

The Antikythera Mechanism. Photo (cc) Tilemahos Efthimiadis.

The Antikythera Mechanism. Photo (cc) Tilemahos Efthimiadis.

This post was chosen as an Editor's Selection for ResearchBlogging.orgSome 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 Dhenry @ Wikimedia Commons.
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