Ana Segawa

The History and Science Behind Eclipses

Ana Segawa

Two weeks ago, on April 8, people got their glasses out and got to witness a total solar eclipse that passed through Mexico, Canada and the United States. What’s the science of predicting these events? What’s the history of eclipses? What was their importance in the past?

The idea of an eclipse seems so simple to us nowadays: it’s a phenomenon that happens when the sun, moon and earth line up, and the moon blocks the sun’s light. But people didn’t understand this back when they started noticing and recording eclipses for the first time. Such a big and mysterious event has been attributed to several causes connected to different superstitions and beliefs in history. [1]

The oldest recorded eclipse in human history may have been on Nov 30, 3340 B.C.E. Eclipses have been surrounded by many superstitions, beliefs, and milestones. Some ancient legends believed that what caused eclipses were creatures like dragons, giant frogs, and even vampires devouring the sun. [2, 3]

Eclipses have played a role in history even if sometimes we don’t pay that close attention to them. It has even been used to name battles due to its impact on history. Thales of Miletus—a pre-Socratic philosopher—reported a total solar eclipse that happened while a war in the sixth century B.C.E. between the Lydians and the Medes was happening. Because of the eclipse, the fighting stopped, and peace was declared, and the battle is now known as the Battle of the Eclipse. [3, 4]

The first person to accurately predict a solar eclipse was the astronomer Sir Edmond Halley, who used Isaac Newton’s law of gravity to do so in 1715. [5] We’ve come a long way to be able to not only understand what an eclipse is but also be able to predict when it’ll happen down to seconds.

The process of predicting eclipses involves working out the geometry and mechanics of the three celestial bodies in a three-dimensional space, then considering their current positions, the speeds in which they move, and putting that into complex equations and using programs to try to set it forward or backward in time to see the positions of the moon and sun from earth’s point of view. [6]

Thanks to how much we have learned about astronomy since 3340 B.C.E., and thanks to all the people in history that documented eclipses and studied them, we can now go outside on a specific day to watch one that has been predicted and instead of fearing the unknown, observe them in wonder!

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