Into hostile territory, at mercy of the map
For centuries, astronomers have realized that total solar eclipses offer a valuable scientific opportunity. During what’s called totality, the opaque moon completely hides the bright photosphere of the sun — its thin surface layer that emits most of the sun’s light. An eclipse allows astronomers to study the sun’s colorful outer atmosphere and its delicate extended corona, ordinarily invisible in the dazzling light of the photosphere.
But total solar eclipses are infrequent, and are visible only from a narrow path of totality. So eclipse expeditions require meticulous advance planning to ensure that astronomers and their equipment wind up in the right place at the right time. As the history of astronomy shows, things don’t always go according to plan for even the most prepared eclipse hunters.
Samuel Williams, the newly appointed professor of mathematics and natural philosophy at Harvard College, was eager to observe a total solar eclipse. He’d seen a transit of Venus in 1769, but had never had the chance to study the sun’s corona during an eclipse. According to his calculations, a total solar eclipse would be visible from Maine’s Penobscot Bay on Oct. 27, 1780.
But reaching Maine from Massachusetts would be something of a problem; the Revolutionary War was raging, and Maine was held by the British Army. The Massachusetts legislature came to Williams’ assistance; it directed the state’s Board of War to fit out a ship to convey the eclipse hunters. Speaker of the House John Hancock wrote to the British commander in Maine, requesting permission for the men of science to make their observations. When the astronomer-laden ship arrived at Penobscot Bay, Williams and his team were permitted to land but restricted to the island of Isleboro, three miles offshore from the mainland.
The morning of the big day was cloudless. As the calculated moment of totality approached, at half past noon, the excitement built. The sliver of uneclipsed sun became narrower and narrower.
Then, at 12:31 p.m., it started becoming wider and wider. Williams realized, to his frustration, that he wasn’t in the path of totality after all. They were 30 miles too far south.
After a subdued voyage back to Massachusetts, Williams tried to determine what had gone wrong. Some astronomers, at the time and in following centuries, suggested his calculations of the path of totality were inaccurate.
Williams, however, had a different explanation. In his report to the newly founded American Academy of Arts and Sciences, he blamed bad maps:
“The longitude of our place of observation agrees very well with what we had supposed in our calculations,” he said. “But the latitude is near half a degree less than what the maps of that country had led
Eclipse