The Antikythera Mechanism is one of the earliest, most complex computers ever devised. Built over 2,100 years ago and recovered from an underwater Roman shipwreck a little over a century ago, this ancient clockwork bronze didn't yield its secrets until the early 2000s, when a cutting edge 3-D X-ray tomography machine the size of a van was transported to Athens to scan the device, which itself could fit in a small box.
PBS' Nova 2012 documentary featured what the X-ray analysis found. We've embedded the full 46-minute documentary below, but we've set it to start at the 16:07 mark, where the first five minutes from this point of the video reveals the researchers' major discoveries about what the device was designed to do and how it worked.
The rest of the documentary is fascinating, where the researchers found astronomical calculations lurking within the gears of the device, which was used to model the cosmos as the Greeks knew it and to predict future events, such as solar eclipses.
Since we're on the cusp of a holiday weekend, we'll share a much shorter video (it's only a minute long) that's somewhat connected, in which the rotation of the Earth over a three hour period is revealed against an unmoving celestial background fixed on the Milky Way: