April 2, 2011
The second century B.C. astronomical calculator found in a shipwreck off the Greek island of Antikythera was even more sophisticated than thought.
Earlier research showed the device also accounted for a subtle weirdness in the motion of the moon. Because the moon’s orbit around the Earth is an ellipse, not a perfect circle, the moon seems to speed up and slow down over the course of a month. In 2006, Tony Freeth of Cardiff University and colleagues showed that a clever configuration of two overlapping gears, with the top gear laid off-center from the bottom gear, could give the moon’s marker its irregular speed.
Because of the Earth’s elliptical orbit around the sun, the sun makes a similarly variable trip across the sky, speeding up and slowing down over the course of the year. But the effect is much more subtle than for the moon.