In the movie Ghostbusters[i], Gozer asks Ray “Are you a God?” After the first disastrous encounter, he is then admonished by Winston: “Ray, when someone asks you ‘Are you a God?’, you say YES!” The problem with that is then you might have to prove your omnipotence. Eclipses often were viewed as supernatural phenomena and when Christopher Columbus found his ship disabled on Jamacia in 1504, He used his almanac to get his crew out of a jam in much the same way the Ghostbusters told Ray to always say “yes” when asked “are you a god?”
Columbus ship needed repairs due to an infestation of shipworms[ii] so they beached it on Jamacia. Initially, the indigenous people of the island welcomed the Columbus and his crew but when some of the members began stealing from them, they cut off their supplies and began to threaten them with attack. Columbus consulted his almanac and was lucky enough to discover that a lunar eclipse was about to happen, thus enabling his escape. The eclipse occurred on schedule, and the astonished Jamaicans promised to resume feeding Columbus and his crew.
This is hardly a new strategy. In Exodus, we see the prophesy of darkness – “And the LORD said unto Moses, stretch out thine hand toward heaven, that there may be darkness over the land of Egypt, even darkness which may be felt….”[iii] When Ezekiel laments the captivity in Egypt and forewarns the people of future captivities in Babylon, he says “And when I shall extinguish thee, I will cover the heaven, And make the stars thereof black; I will cover the sun with a cloud, And the moon shall not give her light.”[iv] When someone asks you ‘Are you a God?’, you say yes.
People have been predicting solar and lunar eclipses for almost 2,000 years, long before they knew what exactly was happening or why it is meaningful. Today, we have a good understanding of orbital mechanics and with the use of computers, we can predict eclipses with very good accuracy, but how do you do this (if you’re not really a god or a prophet) without advance mathematics and computers.
Every agriculturally based civilization developed a calendaring system so that they could predict the best time for planting. The most ubiquitous of these were based on the cycles of the moon and before long, people began to notice patterns. One of the clearest patterns for predicting solar eclipses is the Saros cycle, first observed by the ancient Mesopotamians. Within a Saros series, solar eclipses occur at intervals of 223 lunar months. Unfortunately, the subsequent Saros eclipses don’t happen in the same place, but one-third of the way around the Earth. It takes three Saros cycles for an eclipse to recur in a similar place as the first one—approximately 54 years later and that instance might occur night and be unobservable but the system works. Another problem with the Saros cycle is that multiple cycles occur at the same time. In North America, we saw an eclipse in 2017 eclipse and will see other (in a different cycle) on April 8, 2024. Given that there are about 40 of these cycles taking place at any given time, and each lasts for about 1,000 years, it’s hard to tell which is part of which pattern without detailed recordkeeping like was done to create Columbus’ almanack.
Another way to predict eclipses is to build a machine that mimics the movements (and the axial tilt) of the earth and moon orbiting the sun. An orrery is a mechanical model of the Solar System that illustrates or predicts the relative positions and motions of the planets and moons. The first accurate orrery was produced in 1713 by Charles Boyle, 4th Earl of Orrery – hence the name. These machines are typically driven by a clockwork mechanism with a globe representing the Sun at the center, and with planets at the end of clockwork driven arms. Moons (when present) then revolve around these planets. As a clockmaker, David Rittenhouse completed an advanced orrery in 1770, that earned him an honorary degree from the College of New Jersey. There were, other attempts to make these models in the past but all were stymied by the issues of scale. The actual size of the solar system (and hence the proportional sizes of the planets and their orbitals) was not fully understood until the Astronomical Unit was calculated following the detailed observations of the Transit of Venus in 1769.
Today we rely on mathematics. Determining when and where an eclipse will occur is really just a matter of geometry. The math is not necessarily hard, but there’s a lot of it. You compute the motion of the Moon’s shadow on a plane that crosses the Earth’s center. This gives us a “shadow cone” can be projected onto the Earth’s surface. To define the Besselian elements of an eclipse, a plane is passed through the center of Earth which is fixed perpendicular to axis of the lunar shadow. This is called the fundamental plane and on it is constructed an X-Y rectangular coordinate system with its origin at the geocenter. The axes of this system are oriented with north in the positive Y direction and east in the positive X direction. The Z axis is perpendicular to the fundamental plane and parallel to the shadow axis. The X-Y coordinates of the shadow axis can now be expressed in units of the equatorial radius of Earth. There are eight parameters plus time so this is a laborious technique really only practical with a computer to crunch the numbers.
All that said, we can now predict eclipses (both solar and lunar) with astonishing accuracy. Which is why, like Ezekiel, I predict that if the GOP proceeds with its nomination of a criminal as candidate for President, the Gods will blot out the sun and cast darkness upon the Earth on April 8! Doubt me, well the moon will turn blood red on September 17th as well! You have been forewarned. Vote for someone else, ANYONE else. The gods are displeased with the lunatics in the GOP and are angry. I know this because, like Ray, I am a god.
[i] 1984 American comedy film Dan Aykroyd and Harold Ramis.
[ii] Teredo worms are marine bivalve mollusks that are notorious for boring into and commonly eventually destroying wood that is immersed in seawater like a wooden sailing ship. They are sometimes called “termites of the sea.”
[iii] Exodus 10:21-23
[iv] Ezekiel 32:7
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