ANCIENT GREEK CALCULATOR
DEVICE “PREDICTED ECLIPSES”
Instrument found in 1901 was millennium ahead of its time, scholars determine
X-TEK GROUP/AFP/GETTY IMAGES
Scientists say the Antikythera Mechanism predicted the motion
of the sun, moon and planets and other astrological events.
Greek sky-watchers in the second century BC built a mechanical calculator that could compute eclipses and motions of the planets — technology more complex than anything the world would see for another millennium, modern scholars have found.
For 2,000 years, this instrument lay on the bottom of the Aegean Sea in the wreckage of an ancient Roman ship. Salvaged in 1901, its 82 surviving fragments have mystified scholars ever since.
Now, scientists from four Greek universities and museums and a Welsh university have used X-rays and CT scans to read faint inscriptions not visible before. And they have pieced together a replica, based on where they think the original fragments belong.
“The mechanism predicted lunar and solar eclipses on the basis of Babylonian arithmetic progression cycles,” they report in the British science journal
Nature. It showed when eclipses of the sun and moon would take place, and where the planets would go.
“Named after its place of discovery,. . . the Antikythera Mechanism is technically more complex than any known device for at least a millennium afterwards.” (Antikythera is an Aegean island.)
The box-shaped instrument had a mix of round and spiral dials on its front and back, each with a pointer in the centre mounted on gear wheels, just like clocks. It was probably turned by hand.
“Astronomy was a highly developed science back 2,000 years ago. The astronomical records of civilizations back 2,000 [or] 3,000 years ago were just amazing,” says astronomer Paul Delaney of York University. “Their accuracy was phenomenal. No television, no computers — everybody watched the sky with great interest and with amazing accuracy. So, figuring out planetary [and] stellar motions was truly bread and butter” to ancient observers.
But building what Nature calls “an analog computer” was something even more advanced.
By about 1700 AD, astronomers were building orreries — mechanical devices that illustrate the relative positions and motions of the planets and moon.
“I’m surprised there was something that intricate that was technically accurate that long ago,” Delaney says.
The gears, at least 30 but perhaps more, were hand-cut from bronze. The Welsh-Greek team found their replica computer shows the Metonic cycle on one dial — the 19-year cycle in which the moon returns to the same point in the sky at the same phase (for example, full or half) on the same date in the year.
One dial shows the Saros scale — a pattern of solar and lunar eclipses that repeats every 223 lunar months. Gears also cranked out motions on a Calippic scale — 76 years, or four Metonic cycles, seen on another dial. Still more dials showed a zodiac, an astronomical calendar and a lunar calendar. Another set of gears accounts for the not-quite regular movement of the moon, caused (we know now) by its not quite-circular orbit.
“The moon goes around the Earth on a regular-as-clockwork basis, right? And the Earth-moon system goes around the sun” like more clockwork, says Delaney. What the ancient Greeks did was build the clockwork.
The knowledge that designed the Antikythera Mechanism was lost under Roman rule, which valued engineering on a heroic scale, but lost track of the heavens.
CanWest News Service
BY TOM SPEARS
(AS PUBLISHED IN THE VANCOUVER SUN, THURSDAY, NOVEMBER 30, 2006)
