The Corona Understood

The quotation from Edmond Halley that began Chapter 5 indicates that, in his day, the corona seen during an eclipse was assumed to be a lunar—rather than a solar—phenomenon. The early modern astronomers Clavius and Kepler thought that the corona was simply the back-illuminated atmosphere of the Moon, although one could raise any number of objections to that interpretation.

The fact that the corona is actually the extended but tenuous atmosphere of the Sun became clear from observations made of the eclipse ofJune 16, 1806. The Spanish astronomer José Joaquin de Ferrer traveled to Kinderhook, just south of Albany, New York, to observe. You may have noticed that "corona" appears to be a Spanish word, and this is why: it was Ferrer who coined the term to describe the crown he saw circling the Sun during totality that day. The pivotal scientific contribution he made stemmed from his measurement of the extent of the corona. Ferrer showed that if it were a lunar atmosphere then it must be 50 times larger than that of the Earth, a notion that made no sense. In consequence he opined that the corona was attached to the Sun. The final proof of this did not come until much later, when the first eclipse photographs were obtained in the 1840s and 1850s, but it was Ferrer who first recognized the origin of the corona.

That is not to say that Ferrer neglected the Moon. Especially in view of our discussion about Baily's beads, it is worth mentioning that the Spaniard also noticed that the irregularities of the lunar surface could plainly be discerned around its periphery. Those, of course, are the cause of the beads of light often seen as totality begins and ends.

The eclipse track proceeded eastwards, then, from Coopers-town to Kinderhook to Salem, plus all places in between. It is sometimes misstated that this was the last total solar eclipse visible from New York City prior to that in 1925, which we will discuss in Chapter 10. However, that is incorrect. Although the eclipse was total in a band stretching across upstate New York, the people in the city never saw less than one-sixtieth of the solar disk exposed, and you have to go several centuries further back—to before the foundation of the city—to find the preceding event.

But what of the track of the eclipse of 1806 further west, in the region of the Great Lakes?

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