How did pre-modern societies predict and observe solar eclipses?
In: Planetary Science
The ancients observed that if you had an eclipse, you were very likely to see a similar one 6,585.3 days (18 years 11 days 8 hours) in the future. This pattern is called a Saros Cycle.
If you had a record of a hundred years or so of eclipses, you had a pretty good table to predict eclipses in the future. Over time, eclipses fall out of this cycle as new ones are added so it’s always going on. There are simple ratios between the calendar, the phases of the moon, as well as the Saros cycle.
The Babylonans and Greeks were very adept at doing this math. In about 100 BCE, the Greeks built the [Antikythera mechanism](https://en.wikipedia.org/wiki/Antikythera_mechanism) which used complex gears to do the same math and predict eclipses by turning a crank.
In 2011, I made a working [LEGO version of the Antikythera Mechanism](https://www.youtube.com/watch?v=RLPVCJjTNgk) updated for the modern calendar and eclipses in the United States. The end of the video shows it predicting today’s eclipse.
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