If you’re one of the 32 million Americans living in the path of the April 8 total solar eclipse, you’ve essentially won the cosmic lottery. Across parts of 15 states and directly above cities like Dallas, Indianapolis, Cleveland and Buffalo, the moon will completely obscure the face of the sun, causing the midday skies to darken, the air to grow cooler and the wispy corona of the sun to emerge. One of nature’s most breathtaking sights will be right outside your front door.

Reaching the path of totality wasn’t as easy for Samuel Williams, a minister, astronomer and Harvard University professor who led an expedition to a total solar eclipse on October 27, 1780. For reasons of scientific interest and nationalistic pride, the government of Massachusetts decided to finance the mission (the first instance of state-sponsored scientific research in United States history), which led Williams into enemy territory during the Revolutionary War.

Throughout history, those precious few moments of totality­—and the rare natural conditions that result—have proved conducive to scientific discovery. During a total solar eclipse in 1868, a French astronomer became the first person to observe helium, spotting the element in the spectrum of the usually invisible corona. In 1919, a pair of astronomers who were watching an eclipse verified Albert Einstein’s general theory of relativity by measuring how the sun distorts the light from other stars.

An illustration of how the lunar distance method works
An illustration of how the lunar distance method works Wellcome Collection via Wikimedia Commons under CC BY 4.0 DEED

The great scientific problem of Williams’ day was determining longitude while at sea. Latitude, the parallel lines that measure a north-south position on Earth’s surface, can be derived fairly easily from the length of the day or the height of the sun and other stars above the horizon. But no natural reference points exist for longitude, the east-west lines that converge at the poles.

One approach to the longitude problem was the lunar distance method, which takes advantage of the relationship between longitude and time. The earth rotates 360 degrees in 24 hours, meaning one hour of time is equivalent to 15 degrees of longitude. “Most longitude schemes were based on this principle and relied on an observer determining the time both where they were and, simultaneously, at a reference point with a known geographical position,” notes Royal Museums Greenwich. “The difficult part was knowing what time it was at the reference location.” Before accurate clocks were widely available, astronomers could figure out this time difference by comparing the distance between the moon and a particular star in their location versus the reference location.

Because the position of the moon during totality and the timing of totality itself were unmistakable, Williams knew that making careful observations of both could help improve the lunar distance method. He was eminently qualified to gather this data: He graduated from Harvard in 1761 and excelled in science and math, missing commencement ceremonies because he was accompanying scholar John Winthrop on an expedition to observe the transit of Venus. At age 22, Williams became the minister of the town of Bradford, Massachusetts, often extolling the importance of reason in understanding God and Christian teachings during his sermons. He also made detailed lunar observations. In 1779, Harvard appointed Williams to a chair position, selecting him to replace Winthrop, who’d held the title prior to his death that May.

“Acting as the designated spokesman for science in the colony” and “following the tradition set by his predecessor” at Harvard, Williams decided to organize an expedition to observe the 1780 eclipse, wrote Robert Friend Rothschild in his 2009 biography of Williams. Using tables that predicted the future position of the moon, the astronomer calculated that totality would pass southeast over Penobscot Bay in what is now south-central Maine, a journey of about 165 miles by sea from Boston. But improving scientists’ understanding of longitude wasn’t his primary motive for sailing out to Penobscot.

“Longitude is a selling point,” says Sara J. Schechner, a historian at Harvard and an expert on historical scientific instruments. “There’s a whole range of astronomical and, in his terminology, natural philosophical, reasons” that Williams had, like observing the corona and solar prominences, measuring how temperature changes, and fine-tuning measurements for the sizes and distances of the sun and moon. Still, “longitude often comes up as a justification for astronomical expeditions,” Schechner says.

In the late 18th century, merchants, naval captains and entire governments alike depended on accurate maps. Like a modern-day scientist who writes a grant application that plays up how their research will benefit the public, Williams understood that he needed to emphasize the eclipse’s value to cartography and navigation to gain support for his expedition.

An astronomical quadrant used to measure Earth's magnetic field during Williams' expedition
An astronomical quadrant used to measure Earth's magnetic field during Williams' expedition Collection of Historical Scientific Instruments, Harvard University
An Ellicott astronomical regulator, or pendulum clock, used during Williams' expedition
An Ellicott astronomical regulator, or pendulum clock, used during the expedition Collection of Historical Scientific Instruments, Harvard University

The plan worked. A petition sent to the Massachusetts House of Representatives, asking for permission and supplies for Williams’ expedition, emphasized that eclipse observations “have been of singular service in determining the longitude of places.” Three days later, the House directed the Board of War to prepare a galley stocked with supplies, affirming that a successful observation would be “of much consequence in science, particularly in geography and navigation.”

By using government resources to support science, Massachusetts broke new ground in U.S. history—a remarkable fact given that the state did so during a costly war. The ship and supplies granted to Williams could have conceivably been used to aid the war effort; the conflict had already left both Harvard and Massachusetts in severe financial straits. “Though involved in all the calamities and distresses of a severe war, the government discovered all the attention and readiness to promote the cause of science,” Williams later wrote.

As the nascent nation fought for political independence from Britain, the U.S.’s leaders expressed a growing interest in establishing a distinctly American tradition of scientific achievement. The eclipse expedition was co-sponsored by the American Academy of Arts and Sciences, a scientific society formed just a few months prior to “cultivate every art and science which may tend to advance the interest, honor, dignity and happiness of a free, independent and virtuous people.” The success of the eclipse expedition, a collaboration between an American scholarly organization, a university and a government body, would showcase the strength of the nation’s civil and political institutions and its readiness for independence.

A painting of the destruction of the American fleet at Penobscot Bay in August 1779
A painting of the destruction of the American fleet at Penobscot Bay in August 1779 Public domain via Wikimedia Commons

But Williams still needed British approval to sail toward totality. At the time, the British controlled Penobscot Bay, and they would be especially wary of any approaching American ships. A year earlier, Massachusetts had sent a 43-ship naval expedition to capture the British garrison at Penobscot. The mission was a disaster, resulting in nearly 500 American deaths.

In a letter requesting permission from the commanding British officer, John Hancock, then the speaker of the Massachusetts House, made no mention of the recent battle. Instead, he encouraged the missive’s recipient to cooperate in the interest of science.

“Though we are politically enemies, yet with regard to science it is presumable we shall not dissent from the practice of all civilized people in promoting it,” Hancock wrote, confident the British would appreciate the value of Williams’ expedition and offer any assistance he might need.

“There’s this attitude that science is something special, and it should rise above the politics of the time,” says Schechner. “The armies are fighting each other,” but in the realm of science, diplomatic relations were “incredibly polite. No one’s saying, ‘Why would I help you? I’m trying to stamp you out.’” Americans held themselves to these same standards: In March 1779, Benjamin Franklin instructed American sea captains to grant safe passage to famed British explorer Captain James Cook should his scientific voyage take him near American ships. (By then, Cook was already dead, killed in a dispute with locals in Hawaiʻi, but news of his demise wouldn’t reach Europe until the following January.)

A reflecting telescope used by Williams' team during the expedition
A reflecting telescope used by Williams' team during the expedition Collection of Historical Scientific Instruments, Harvard University

Williams received British assurances that his ship wouldn’t be fired upon but was forbidden from stepping foot on the mainland and ordered to return home immediately after the eclipse. Though the British understood the importance of the eclipse expedition, they feared that Williams would pass information to American ships or troops if allowed to linger in British territory.

Accompanied by a team of nine assistants and Harvard’s impressive collection of astronomical instruments—including telescopes, compasses, clocks and quadrants—Williams set sail for Penobscot, choosing to disembark at Islesboro Island, a narrow, 14-mile-long island situated in the middle of the bay. The group arrived on October 17, ten days before the eclipse, giving the researchers time to set up their instruments, calibrate the clocks and determine their latitude.

Cloud cover threatened to ruin the expedition, but sunny skies prevailed on October 27. Williams aimed his telescope at the gradually disappearing sun and recorded at two-minute intervals the precise percentage that remained visible as the moon gradually shifted in front of the star.

Williams' sketch (top right) of the "small drops or stars" he observed through his telescope
Williams' sketch (top right) of the "small drops or stars" he observed through his telescope Biodiversity Heritage Library

What Williams saw next was a rare sight, previously observed by only a select few. When a tiny sliver of sunlight remained in the darkened sky, Williams looked through his telescope and saw what he would later describe as “small drops or stars; some of which were round, and others of an oblong figure.” He’d witnessed what are now called Baily’s beads, bright spots of sun that appear just before totality, as the mountains and valleys on the moon’s surface either block or allow sunlight to pass through.

These “small drops or stars” occupy just a few sentences in Williams’ report. It wasn’t until 1836 that the eponymous English astronomer Francis Baily wrote a more complete record of the phenomenon after seeing it during that year’s eclipse, describing the spots as a “string of bright beads.” Had Williams paid more attention, modern scholars might very well call the effect Williams’ drops instead of Baily’s beads.

Just before totality was scheduled to begin, Williams’ expedition experienced the greatest possible disappointment: light. Instead of obscuring the last drops of visible sunlight, the moon receded from the sun, gradually releasing sunlight and warmth. Williams and his crew had narrowly missed out on seeing the total solar eclipse.

Researchers are unsure what led the team astray of totality, which passed about 35 miles north of the expedition site. In addition to expressing frustration with the British officer for imposing constraints on the expedition, Williams faulted the maps he’d used for leading him south of totality’s path. The scientist also could have erred himself, miscalculating the exact path of the eclipse based on the available lunar tables, which themselves had errors potentially significant enough to direct Williams away from totality.

A 2019 photo of Baily's beads, also known as a double diamond ring eclipse
A 2019 photo of the double diamond ring effect, which is caused by the same phenomenon as Baily's beads CTIO/NOIRLab/NSF/AURA/D. Munizaga via Wikimedia Commons under CC BY 4.0

Regardless of who or what deserves the blame, the expedition still yielded valuable results. Williams’ data allowed him to derive an accurate longitude for Cambridge, Massachusetts, enabling ships to better navigate in New England. Williams published his detailed eclipse observations, including how the temperature changed and which planets and stars became visible, in the inaugural volume of the American Academy of Arts and Sciences’ scientific journal, contributing to the growing body of American scientific research.

“[Williams] would be disappointed he didn’t see the full phenomena after going through all this trouble,” says Schechner. “But I think he would have also recognized [that it] was an achievement to put this together.”

Despite his failure to witness totality, Williams was among the first in a long line of Americans enthralled by the chance to see a total solar eclipse. A few weeks before the 1780 eclipse, he urged his fellow New Englanders to make their own eclipse observations with telescopes. Few readers would have had the means or motivation to heed Williams’ call, especially as the Revolutionary War raged on. But next week, on April 8, an estimated one million to four million Americans with smartphones, telescopes and eclipse glasses in hand are expected to travel to the path of totality, joining the tens of millions who live there already.

Williams never got the chance to embark on another eclipse expedition. In 1788, he abruptly resigned from his post at Harvard amid accusations of forgery and failing to repay his debts. Then he absconded to Rutland, Vermont, where he died in 1817 and is buried today.

Two centuries later, totality will pass about 35 miles north of Rutland on its arc from Texas and the Midwest to upstate New York and northern New England—the same discrepancy between the predicted and actual location of the 1780 eclipse. For Williams, it will once again be a near miss.

What Is a Solar Eclipse?

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