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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