How did the Antikythera machine actually work?



I know there were cogs that predicted eclipses but how do cogs predict eclipses??

In: Technology

The machine modelled the movements of the earth and moon around the sun do that future alignments could be predicted. The cogs modelled the relative speeds of rotation.


There’s a fantastic YouTube channel where a guy is re-creating the machine by hand using only tools and methods available at the time. It’s called Clickspring. He goes into a lot of how the machine works.

Basically, all celestial motion is circles, and those circles happen at different rates. The earth rotates on its axis once per day, the moon rotates around the earth once every 30 days, the Earth goes around the sun once every 365.25 days, and the Earth has an axial tilt of 23.4 degrees. That means that depending on where the Earth is in its revolution around the sun, the sun will appear higher or lower in the sky. So what we need to find is a situation where the moon is between the earth and sun, the sun is at the right height at that time of day, and the observer is on the side of the Earth that’s facing the sun. By using gears sized proportionally to each of those rotation times, you can track the movement of the Earth, Sun, and Moon in relation to each other at any point in time, then its just a matter of turning a drive gear an appropriate amount for the passage of time, and you can observe when the conditions for an eclipse will be met.

From what I understand it was basically a clock that was hand operated. you’d set the date, and it would give you some information, I don’t think it’s actually known what specifically it was keeping track of, probably the location of key navigational stars and planets, there’s a predictable pattern to eclipses so that could be part of it.