What is the Antikythera mechanism?

The Antikythera mechanism is the oldest analogue computer in the world, made around 80 B.C. by the Ancient Greeks who knew why we have seasons such as Spring.  

It was found in a Roman shipwreck near the island of Antikythera (literally “opposite Kythera”- another Greek island) in 1901 by a group of sponge divers.

In appearance, it was a lump of wood and a corroded cluster of bronze gears. It was ignored at first, until Derek de Solla Price, a British scientist became interested and made X-ray and gamma-ray images of the 82 fragments. It seemed to be made of a low-tin bronze alloy of approximately 95% copper, 5% tin, and its instructions were composed in Koine (Biblical) Greek.

It turned out to be a computer which, by turning a hand crank could calculate astronomical positions and eclipses for calendar and astrological purposes decades in advance.

It could also be used to track the four-year cycle of athletic games which was similar to an Olympiad, the cycle of the ancient Olympic Games. Replicas have been made which work perfectly.

The quality and complexity of the mechanism suggest that it might have had predecessors made during the Hellenistic period. Its construction relied on theories of astronomy and mathematics developed by Greek astronomers during the second century BC, and it is estimated to have been made around 87 BC and lost a few years later.

This astronomical knowledge was lost until modern times, but it shows that the Ancient Greeks knew even more than we thought. For example, they knew why we have seasons.

planet and moon

It took the Ancient Greeks to figure out the reason why there are seasons, and modern scientists to find the reason for the reason. The simple answer is that the Earth is tilted on its axis at 23.4° degrees.

As it makes its year-long journey around the Sun, Greece in the Northern Hemisphere is leaning towards the Sun for half the year, and leaning away from it for the other half. Although the strength of the Sun remains constant, it falls on a greater area in the winter than in the summer and a smaller area in the summer.

This varying relative strength of the sunlight on Earth and length of the days brings longer, hotter days in summer and shorter, colder days in winter. Increasing day length and temperature initiate most of the changes we call spring. If all of this is hard to visualise, walking around a standard lamp (the Sun) with a tilted revolving globe (the Earth) may make it all clear.

Why is the Earth tilted? It seems that early in the Solar System’s history something very big hit the Earth and whacked it out of kilter. The bits that flew off whirled around, collected together and became the Moon. Put like that it sounds about as likely as any other creation myth, but that is the accepted theory.

What interests me is how contingent it all is: without that collision there would not only be no seasons, but possibly no living creatures either. Our disproportionally large moon drove tides which are now thought to have provided the conditions that gave rise to life.

If you are interested in how the Ancients figured out why we have seasons and many other facts about the Antikythera era you might like to read my book about the season of Spring.