The Antikythera Mechanism [1, 2, 3] is the oldest known scientific computer, built in Greece at around 100 BC. Lost for 2000 years, it was recovered from a shipwreck in 1901 (off the Greek island of Antikythera). But not until a century later (2006) was its purpose understood, with the help of high-resolution X-ray tomography: an astronomical clock that determines the positions of celestial bodies with extraordinary precision (predicting celestial events and eclipses).
In 2010, Andrew Carol built a fully-functional replica out of LEGO.
It is not the first reconstruction of the original bronze mechanism, but certainly the most interesting one for the vast majority of th AFOL community.
The original ancient mechanism used gears of unparalleled precision. Its LEGO replica uses 1500 Technic parts and 110 gears (probably more than twice from the original).
"The remaining fragments of the Antikythera Mechanism contain 30 gears. Most of these (27) are to be found in Fragment A. Fragments B, C and D contain one gear each. These gears are not sufficient for the mechanism to fulfil its known functions, and a further 5 gears are required. However, this scheme leaves a lone unused gear in Fragment D. This is probably part of the missing epicycle gearing that modeled Hipparchos’s solar model, and the planetary mechanisms. The total number of gears in the Mechanism depends upon how many planets the mechanism modelled, and how accurately their motions were modelled." 
Divided in a central part and two "wings", each featuring four gearboxes for distinct mathematical operations, it performs the same calculations as the original mechanism.
This work was sponsored by Digital Science a new division of Macmillan Publishers that provides technology solutions for researchers.
The activities of Digital Science build on the reputation for editorial and technological excellence of its sister company, Nature Publishing Group (NPG), but focus on technology-based solutions for research rather than scientific content.
The astonishing video is the result of 40 days of stop-motion film making. See it how, from this "Behind the scenes" video.
I was dazzled when I saw it for the first time!
Thanks to one of our readers (grindingears), who told us about a webpage from the author of this machine, with documentation and the maths about his magnificent project.
Last Update: 2010.Dec.12 21:16 CET