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Simon Newcomb’s Curious Eclipse

Presentation #322.03 in the session HAD III: Oral Presentations.

Published onJun 29, 2022
Simon Newcomb’s Curious Eclipse

Every astronomer has had his or her observing plan go awry. The same was true in the 19th century.

In 1869, A total eclipse of the Sun was to be visible diagonally across the United States. For the first time, many astronomers — including Simon Newcomb — traveled to observe such an event.

Before leaving Washington, Newcomb scheduled all that was supposed to happen. Upon arriving at Des Moines, Iowa, he attached to the county courthouse (his temporary “observatory” grounds) “screens” of different angular sizes. He intended to block most of the apparition in order to better see various total-eclipse phenomena far from the center of the Sun—perhaps even the imagined planet Vulcan.

His principal observational target was the corona, of which little was known. This study should not take too long. Everyone had been told by those who had seen it before that there would not be much to see.

During the real 1869 total eclipse of the Sun, this program went out the proverbial window. Long creamy streamers radiated from the corona. The Sun was no longer a circle. Newcomb was soon transfixed by what he was seeing. The language used by this man of numbers is remarkable: The solar corona was, “glorious beyond description … Its structure was not uniform …”

The most common description of the corona’s shape by the peregrinating mathematicians observing the total solar eclipse was that of a “trapezoid.”

Newcomb abandoned his telescope, which he had chaperoned all those many kilometers, and examined the corona with his naked eye.

The story of carefully laid observing plans being hijacked by a compulsion to gawk, without anything between the witness and the spectacle, was repeated over and over during the 1869 total eclipse of the Sun. As Samuel Langley explained, “Special observations of precision in which I engaged would not interest the reader; but while trying to give my undivided attention to these, a mental photograph of the whole spectacle seemed to be taking without my volition.”

The 1869 corona was not what astronomers had expected. It always had been depicted as a more circular ring without further morphology. The most recent total eclipse, well-observed by astronomers, was that of 1860.

The year 1860 was a sunspot maximum year. The Sun was halfway through its eleven-year cycle. During the next cycle, the year 1869 occurred after sunspot minimum had just passed, in March 1867. The result was a brighter but more asymmetric and less broad corona than astronomers had been led to believe they would encounter.

From the 1869 TSE on, the nature of the corona became a driving force in the study of the Sun. American astronomers would participate significantly.

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