Babylonian tablets suggest that Earth’s rotation is slowing less than expected.
On the morning of April 15, 136 B.C.E., residents of the ancient city of Babylon, in what is now Iraq, experienced quite a sight. An hour and a half after sunrise, the moon moved across the face of the sun, blotting it out so only the golden halo of its atmosphere was visible. The sky went dark.
“Venus, Mercury and the Normal Stars were visible; Jupiter and Mars, which were in their period of disappearance, were visible in that eclipse,” a Babylonian astrologer inscribed in cuneiform, on a clay tablet now stored in the British Museum.
To measure the eclipse’s duration, the astrologer would have used a cylindrical vessel called a clepsydra, or a water clock, whose slow draining marked the passage of time. “It moved from SW to NE. 35 us [time duration] for obscuration and clearing up. In that eclipse, north wind which...” The rest of the observation is on a missing chunk of tablet and was lost to history, but the astrologer may have been noting that the wind shifted direction, which happens during a total eclipse.