Babylonian Predictions of Lunar and Solar Eclipse Times

The Late Babylonian astronomers of the last seven centuries B.C. recorded many observations of lunar and solar eclipses in their astronomical records - clay tablets which are now largely in the British Museum. These records also contain predictions of the times of eclipses; whether the eclipse was expected to be visible or not. Comparison of 40 lunar eclipse predictions with computation has revealed that over half relate to real umbral eclipses that were visible somewhere on the Earth's surface. Most of the others correspond to penumbral eclipses. Analysis of the umbral eclipses has revealed that the recorded time of the prediction specifically relates to the expected time that the eclipse would begin (i.e., first contact), and that the typical accuracy of the prediction was just over one hour. Comparison of 61 solar eclipse predictions with computation has revealed that all of the predictions relate to events that were visible somewhere on the Earth's surface, however often far away from Babylon. This represents a remarkable achievement. Almost half of the eclipses would have been visible if the Sun had been above the horizon at the time of the eclipse (i.e., the eclipse was visible at the latitude but not necessarily the longitude of Babylon). The typical accuracy of these predictions was just under two hours. There is no evidence of any improvement in the accuracy of the prediction of lunar and solar eclipse times over the Late Babylonian period. The predicted times are of significantly poorer accuracy than the times of observed eclipses, which are typically accurate to about half an hour. This suggests that whenever an eclipse was observed, the time of the eclipse was measured and replaced the predicted time in the astronomical record.