Welcome to the dark side. On Monday, Aug. 21, a total solar eclipse will immerse a sliver of the United States into an eerie cast of nocturnal darkness during what are typically daylight hours.
As you can imagine, finding yourself suddenly shrouded in a dusky shadow in the middle of the afternoon with no prior knowledge might be a bit unsettling! Before the advent of modern science, eclipses were an enigma sometimes suspected to portend trouble and the end of times. They clearly had a profound effect on past civilizations, and their accounts found their way into ancient texts.
Even into the 21st century, they have continued to be a source of awe, while simultaneously helping us better understand the universe.
One of the first documented efforts to predict the occurrence of an eclipse dates back thousands of years ago. The Chinese astronomers Ho and Hi allegedly failed to forecast an eclipse on Oct. 22, 2136 B.C. They were reportedly “hanged because they could not spy Th’eclipse, which was invisible,” an ancient text said.
Homer, the famous Greek poet and author, made reference to an apparent eclipse in his renowned story “The Odyssey” (thought to have occurred several centuries before his birth). NASA claims that the eclipse Homer described likely occurred April 16, 1178 B.C., and cast a northeastward-moving veil of blackness over much of the Mediterranean, passing directly over Greece. In his passage, Homer recounts “the Sun has perished out of heaven, and an evil mist hovers over all.”
Some biblical texts suggest eclipses were an omen of doom. For example, in Amos 8:2, the Lord describes Israel as a “basket of ripe fruit,” a metaphor hinting that Israel was primed for judgment. The Lord then asks “when will the new moon be over?” He subsequently threatens in Amos 8:9 that “I will make the sun go down at noon and darken the earth in broad daylight.”
This same eclipse also seems to have been referenced in the Assyrian Chronicles, ancient texts written in Babylon. The texts are carved in stone tablets, and report of “insurrection in the city of Ashur” when “in the month Sivan, the Sun was eclipsed.” Ashur is a city in present-day Iraq, north of the Tigris River near the Iranian Plateau. This description appears commensurate with an eclipse NASA calculated to have occurred in 763 B.C. across the Middle East. Clearly, solar eclipses play a relatively jarring role in religious tradition.
Moving to more modern times, journalists throughout the 18th and 19th centuries revered the opportunity to chronicle an eclipse. Sidney Perley, a lawyer in Salem, Mass., wrote of a “total eclipse of the sun” on June 16, 1806. According to Perley, the temperature dropped with “a diminution of seven and one-half degrees” during the eclipse. Perley was devoutly religious, and oftentimes interpreted natural occurrences as negative omens; he even claims that “several died from [the eclipse’s] effects.” Venus and Mercury both were visible during totality, as well as a number of stars. Perley writes that “a feeling of awe came over the people,” while cattle “ceased feeding” and birds “retired to their roosts.”
Despite the panic and alarm that at one time was synonymous with the word “eclipse,” researches have benefited immensely from their visitations in the modern era.
In 1919, an eclipse proved vital to Albert Einstein as he worked to confirm his theory of general relativity. Having posited his idea four years earlier, his theory suggested that, while Isaac Newton’s laws would hold true, space and time could behave differently in the pretense of large gravitational fields. In other words, Einstein’s theory dictated that light beams could actually be bent by the gravitational fields around massive objects. Unfortunately, the only way to test this theory was to encounter an enormous object, and the only one that proved large enough was the sun.
Unfortunately for Einstein, the sun also happens to be a brilliantly luminescent source of light — as such, it would be impossible to detect light bending around it, as it would be outshone by the gaseous giant itself. But Arthur Stanley Eddington, a top physicist in the United Kingdom, had a solution: during a solar eclipse, sunlight is blocked out for several minutes, allowing for a cluster of stars to appear around the concealed solar disk.
Using this knowledge, Eddington headed to the island of Principe along the West African Coast to photograph the May 29, 1919, eclipse. During the instant of totality, his team shot a number of close-range photographs of the combined moon/sun pair, and in the coming weeks quickly processed their data and calculations; it was soon revealed that Eddington was able to view stars that should have been hidden behind the sun, but given the bending of light commensurate with Einstein’s theory of general relativity, they were in fact perceptible. Thus, Einstein’s theory became an overnight success story, marking the first occasion on which qualitative scientific evidence could be used to confirm such an earth-shattering theory. Nowadays, scientists are actually forced to compensate for this effect when making measurements of distant galaxies — it’s been dubbed “gravitational lensing.”
The upcoming eclipse will also present a myriad of opportunities for scientists.
Across the country, both amateur and professional scientists are gearing up for what is sure to be the celestial spectacle of the decade. The last “coast-to-coast” solar eclipse in the United States occurred on June 8, 1918, making this month’s the most widely-viewable eclipse on U.S. soil in nearly a century. FiveThirtyEight’s Rebecca Boyle details some of the “cool science” in the works for the big day.
Looking to get in on the action yourself? Fortunately, you can! NASA is encouraging citizen scientists to engage in eclipse monitoring and to submit anything from “basic observations” to “publishable research.”