An American astronomical evangelist coined the phrase ‘island universe’

No other science engages human curiosity like astronomy. From antiquity onward, attempts to comprehend the architecture of the cosmos have commanded a substantial fraction of humankind’s mental budget for intellectual endeavor. Only in the last century, though, have astronomers grasped the structure of the cosmos accurately. Just a hundred years ago, a great debate raged about the fuzzy patches on the nighttime sky known as “cloudy stars,” or nebulae.

Some astronomers believed that those cosmic fuzzballs resided within the Milky Way, the galaxy containing the sun and billions of other stars. In those days the Milky Way essentially comprised the known universe. But some experts suspected the nebulae to be very distant stellar systems much like the Milky Way itself — “island universes” populating the vastness of space. Skeptics argued otherwise, contending that the nebulae would be impossibly far away if they contained stars similar in brightness to the sun. In October 1917, the prominent astronomer Harlow Shapley reported that the brightness of novae in various nebulae would place some of them millions of light-years away, in conflict with other measurements of rapid internal motion within the nebulae. (At such large distances, internal motion would not be perceptible.) “Measurable internal proper motions,” Shapley wrote, “can not well be harmonized with ‘island universes’ of whatever size, if they are composed of normal stars.”

The centennial of Shapley’s paper is not being widely celebrated, of course, because he was wrong — distant nebulae are, in fact, island universes (the measurements of internal motion supposedly ruling that out turned out to be bogus). But there is another anniversary worth celebrating this year — the dodransbicentennial (or dodrabicentennial) of the founding of the Cincinnati Astronomical Society in 1842. That event is noteworthy for its connection to one of astronomy’s greatest mysteries: who first coined…

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