An eye for an i #369 Children

The eclipse chaser of 1780

People gather to watch a total solar eclipse in La Higuera, Chile, on July 2, 2019. Back in 1780, it wasn’t as simple as this...   | Photo Credit: AP

Witnessing eclipses, be it solar or lunar, is rather easy these days. The event and the day in which it will be taking place is predicted well in advance (each and everyone that has and will be taking place this century is already listed along with various details, including date, time, magnitude and geographical area it can be seen in). If you are in the region where it can be witnessed, or travel to the place if you are an enthusiast, then it is only a matter of getting your equipment and waiting for the event to take place.

It wasn’t always this way, though. For starters, humanity might well have feared such occasions. Records show that Babylonions and the ancient Chinese were able to predict solar eclipses almost 4,500 years ago. But it was only in the second half of the previous millennia that a scientific approach towards these phenomena was adopted.

Scientific approach

Once people started looking at these events from the perspective of science, it became all the more important to observe and record maximum detail. It was under this climate that the Americans sent their first expedition to observe a total solar eclipse that took place on October 27, 1780. The man at the helm of this expedition was Samuel Williams.

Born on April 23, 1743 as the ninth child of Reverend Warham Williams and his wife Abigail, Williams graduated in absentia in 1761, tenth in his college class of 41. He missed the commencement exercises as he was on a scientific expedition with the distinguished mathematician, physicist and astronomer, John Winthrop. Along with Winthrop, the second Hollis Professor of Mathematics and Natural Philosophy at Harvard College, Williams had the opportunity to observe the transit of Venus in Newfoundland.

Following his graduation, Williams taught for a few years before serving a ministerial position in Bradford, Massachusetts, the U.S., from 1764-79. In 1780, Williams not only became one of the founding members of the American Academy of Arts and Sciences, but also succeeded Winthrop as the third Hollis Professor of Mathematics and Natural Philosophy at Harvard College. In that same year, he was also chosen by the Academy to head an expedition to view the total solar eclipse that was to take place on October 27.

Behind enemy lines

While observing a total solar eclipse was in itself a rarity in those days, the favourable opportunity afforded a chance to measure the longitude as well based on the difference between the observed time of the eclipse and the theoretical time as calculated from tables. There was, however, a catch as the eclipse took place while the Revolutionary War was on. And there was the added complication that the best place to view it was Penobscot Bay, still under the control of the British.

Even though Williams was able to obtain permission from the occupying British forces to cross the enemy lines, the expedition party, which also included three assistants and six students, were restricted to the island of Islesboro, nearly five km offshore from the mainland where they wanted to observe.

Global map of the 1780 total solar eclipse.

Global map of the 1780 total solar eclipse.   | Photo Credit: NASA/Wikimedia Commons

Having sailed to their destination with their telescopes, they set up their instruments, in preparation for the big event scheduled at half past noon on October 27, 1780. The excitement rose as the part of the sun not eclipsed became narrower, but it then started becoming wider in some time. The moment of totality was lost.

Was it a failure?

There are many who call the expedition a failure as it wasn’t able to record the totality. Whereas some believe that Williams was unable to calculate the path of totality correctly, Williams himself, and many others as well, suggest that the maps available then were not accurate enough, meaning that the path of totality actually went further north of Williams’ location. The results of the expedition were published by Williams in the very first volume of the Memoirs of the American Academy of Arts and Sciences (1780-83).

It is interesting to note that Williams’ account includes a vivid description of Baily’s beads and that the memoir even had a figure of what the expedition saw. The Baily’s beads effect, or the diamond ring effect, is a well-known effect now wherein a ring of beads is seen around the edge of the sun as it approaches total darkness. It is named after English astronomer Francis Baily, who explained the phenomenon in 1836. Considering that Williams’ observations came over half-a-century earlier, Baily’s beads could well have been Williams’ wampum...

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Printable version | Nov 30, 2020 5:32:31 PM | https://www.thehindu.com/children/the-eclipse-chaser-of-1780/article29656910.ece

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