A Brief History of Solar Eclipses

By Megan Giddings

Posted August 11, 2017

This is the second part of our eclipse series in anticipation of the solar eclipse happening on August 21, 2017. If you missed part one, it can be found here.

In the past, there were multiple explanations for what a solar eclipse was. In Homer's Odyssey, a total solar eclipse was thought to be the death of all that is good. An ancient Korean myth involved attempted thefts by a band of fire dogs. The explanation for the eclipses was that while the dogs never stole the sun or moon, they did get in a good chomp.

There are several instances of scientists throughout history attempting to explain solar eclipses without invoking curses, plagues, and mischievous mystical animals.

There are several scientists to thank for our modern understanding of solar eclipses work. Chinese scientists in 20 BCE were already calculating when solar and lunar eclipses would take place. Thales is thought to have accurately predicted a solar eclipse in 585 BCE. The scientist that many attribute the scientific foundations for how we understand solar eclipses today is Johannes Kepler.

Kepler

While it was Copernicus who theorized that the sun, not the Earth as it was commonly believed then, was what things orbited around, Kepler defended Copernicus's position, as well as built upon it.

While Kepler discovered many things (outside of astronomy, he's attributed wth creating lenses that correct near and far sightedness), there are three laws that he's famous for.

Three Laws

In as basic of explanation as possible, Kepler's three laws are: that all planets in the solar system move in elliptical orbits around the sun; a straight line drawn from the sun to a corresponding planet will sweep out in equal parts; and the third law is "the ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun."

What these three laws are about is calculating distance, speed, time, and mass. There is much, much, much more to these laws and Kepler's work than what is described here. The main thing to take away here is that these laws help today's astrophysicists calculate the motion of objects in our solar system, as well as to discover planets in other distant parts of the universe.

Being able to calculate these things lets scientists estimate when eclipses and other conjunctions such as a syzygy will take place.

Newton and Galileo

Kepler's theories were based upon work down by Sir Issac Newton and Galileo. Galileo continued to build on theory Copernicus held that the Earth was not the center of the universe by observing Jupiter's moons and how they clearly were not being governed by Earth.

And Newton proved that the laws of motion regarding celestial bodies also applied to motion on Earth as well.

Halley's Broadsheet

Work by the three of them was used by Edmond Halley. While Halley is probably most known for his work on what's known as Halley's Comet, he predicted an eclipse 302 years ago. He used calculations based upon work by Kepler and Newton to create an broadsheet that was available in England in advance of the eclipse.

Halley's broadsheet was only 4 minutes off in predicting when totality would occur. What is also noteworthy is in that broadsheet, he encouraged the citizens of England to make their own observations of the solar eclipse to help further understanding.

If you're in the United States and want to help continue expanding knowledge about solar eclipses, consider joining NASA's GLOBE experiment. Citizen scientists participating in GLOBE will need to download the free app, obtain a thermometer, and need to be able to record air temperature and cloud data.