An American astronomical evangelist coined the phrase ‘island universe’

Anniversary of Cincinnati astronomy society spotlights Civil War general Ormsby MacKnight Mitchel

A view deep into space from the Hubble Space Telescope shows numerous galaxies, huge collections of stars like the Milky Way. A century ago, astronomers called those galaxies “island universes,” a term introduced by Civil War general Ormsby MacKnight Mitchel.

NASA, ESA, G. Illingworth, D. Magee and P. Oesch/UCSC, R. Bouwens/Leiden University, and the HUDF09 Team

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 the phrase “island universe.” (A mystery that will be solved by the end of this blog post.)

Often that honor is attributed to the philosopher Immanuel Kant. But Kant wrote in German, and he didn’t use any phrase that could be translated as “island universe.” He was among the first to figure out the nature of the Milky Way, though. From ancient times, skywatchers had wondered at the eerie dim glowing band of light visible across the nighttime sky (until modern light pollution drowned it out). Galileo’s telescope revealed within the milky glow a vast population of stars too distant and dim to discern with the naked eye. More than a century afterward, in 1755, Kant reasoned that the Milky Way was actually a large lens-shaped disk, a system of stars (including the sun) analogous to the sun’s system of planets. In essence, the Milky Way was the universe, a grand collection of countless worlds — stars surrounded by planets, possibly inhabited. Kant further speculated that the Milky Way was not alone. Nebulae, it seemed to him, were too big to be merely dim fuzzy stars. He deduced them to be at a great distance (too far for their individual stars to be detectable), each of them another entire “universe” like the Milky Way.

But he didn’t call them islands. When he used the German word for island (Insel), he was referring to things like Jamaica, or an uninhabited planet. When Kant said “these elliptical figures are just universes,” the actual term he used in German was Weltordnungen, which is literally translated as “world orders” (or in some places Weltgebäuden or Weltsystemen, world systems).

Kant was right about the nebulae; Edwin Hubble established the reality of island universes in the 1920s. Today, of course, they are called galaxies (although Hubble preferred “extragalactic nebulae”). Hubble credited the phrase “island universe” to the German naturalist and prolific popularizer of science Alexander von Humboldt, famous for his multivolume Kosmos (an attempt to survey the entire scope of scientific knowledge). Von Humboldt discussed the problem of the nebulae in Volume 3, published in 1850, referring to them in German as Weltinseln. Hubble took that to mean “island universes,” and wrote that Humboldt used it in Kosmos in 1850 “presumably for the first time.”

But as Hubble noted, the first English translations rendered Weltinseln literally, as “world islands.” “The transition to ‘island universes’ is an obvious step, but the writer has not ascertained the first use of the term,” Hubble wrote in The Realm of the Nebulae. Modern historians have taken Hubble’s explanation at face value. In fact, though, von Humboldt was not the first to use the term Weltinseln to refer to the nebulae as distant galaxies. And the honor for first use of “island universe” in English belongs to a Union general of the American Civil War: Ormsby MacKnight Mitchel, founder of the Cincinnati Astronomical Society.

Mitchel was born in the Kentucky wilderness in 1809 (or 1810) but grew up in Lebanon, Ohio. With the aid of U.S. Postmaster General John McLean (who lived in Lebanon), Mitchel gained admission at age 16 to West Point. There he studied astronomy among other things (such as engineering), graduating in the same class as Robert E. Lee. Mitchel continued on at West Point to teach math and then served on active duty in Florida. But soon he returned to Ohio, studied law, worked for the railroad (as a civil engineer) and became a professor of math and astronomy at Cincinnati College. 

Mitchel was slight and short (about 5-foot-6, and could have boxed as a featherweight) but was a dynamic lecturer, something of an astronomical evangelist. In 1842, after one of his lectures, he announced the 19th century version of a Kickstarter campaign: He planned to build the country’s best astronomical observatory in Cincinnati. Anyone who contributed (he asked for a $25 minimum) would become an original member of the Cincinnati Astronomical Society — and would be allowed to look through the new telescope. Money poured in, and Mitchel arranged for a top German firm to build a 12-inch refractor, bigger at the time than any other telescope in America. He managed to get the observatory built in time for the telescope’s delivery in January of 1845. One slight problem was the lack of funds for any observatory staff. But Mitchel decided he could run it on his own; his salary from the college was enough, he thought.

But just days before the telescope arrived from Germany, Cincinnati College burned down, leaving Mitchel unemployed. He had a wife and seven kids. So Mitchel needed a new business model, quick. He decided on a three-pronged strategy: going on the lecture circuit, delivering talks on astronomy to audiences in several major cities around the country; writing books; and launching a new monthly astronomy magazine, with a subscription price of $3 per year: The Sidereal Messenger. It was in this magazine that the English phrase “island universe” was first used (as far as anybody knows) to refer to the distant nebulae.

In July 1847, for instance, Mitchel’s magazine referred to 10 nebulae in the constellation Ursa Major: “How wonderful is the thought that space is so richly strewn with these island universes,” he wrote. He also used the phrase in an 1847 lecture. “Next to the Milky Way, the object is to find what is beyond. Is there anything beyond? Have we reached the end? No; if we were there we should find 10,000 mighty island universes beyond, whose suns must be at least 1000 millions.”

But the first appearance of “island universe” came in October 1846, in a long article by the eminent astronomer Johann Heinrich von Mädler. Mädler’s article refers to “our island universe (since, with reference to the distant nebulae, the entire combination of fixed stars within the Milky Way may be thus designated).” Credit for “island universe” does not therefore belong to Mädler, though — the article in Sidereal Messenger was Mitchel’s translation of a paper by Mädler published earlier in 1846 in Astronomische Nachrichten. In the original German, Mädler used the term Weltinsel — world island — just as Humboldt did four years later in Volume 3 of Kosmos. So it was Mädler, not von Humboldt, who first referred to nebulae as Weltinseln, or world islands, and Mitchel who first rendered that phrase into “island universes.” (Unless, of course, he encountered the phrase from someone who used it earlier but left no trace in the annals of history or records accessible by Google.)

To be fair, Mädler might have borrowed Weltinsel from von Humboldt. It turns out that von Humboldt had in fact used Weltinsel earlier — in Volume 1 of Kosmos, published in 1845, the year before Mädler’s paper appeared. But in this place von Humboldt used Weltinsel just to refer to the Milky Way, not the far-off nebulae. And the English translator rendered it as “cosmical island,” not quite the same grandeur as “world island.” It is likely that Mädler would have read von Humboldt’s book; after all, it was von Humboldt who helped Mädler become an astronomer in the first place. In 1824, von Humboldt introduced Mädler to the wealthy banker Wilhelm Beer, who built an observatory for Mädler to conduct astronomical observations.

As for Mitchel, he used the phrase “island universe” repeatedly in his writings and lectures throughout the 1850s. It was also used by other astronomers (such as Denison Olmsted of Yale, who referred to island universes in his Franklin Lectures of 1852) and was adopted by nonastronomers by the 1860s. The date of first usage recorded in the Merriam-Webster dictionary is 1867.

But that was after Mitchel died. With the outbreak of the Civil War, Mitchel was called to active duty in the Union army as a general. (For some reason the troops nicknamed him “Old Stars.”) He commanded the Ohio volunteers for a while and led a raid that took control of Huntsville, Ala. He was later assigned to a post in South Carolina, where he promptly caught yellow fever and died, on October 30, 1862.

A few years later new observations showed some nebulae to be primarily gaseous, dashing the enthusiasm for nebulae actually being island universes full of stars. By the late 19th century most experts denied that other “universes” existed beyond the Milky Way itself. But it turned out that not all nebulae were alike, and some — known as the spirals — are in fact “island universes,” as Hubble proved in 1923. And that will be another excellent anniversary to celebrate.  

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Tom Siegfried is a contributing correspondent. He was editor in chief of Science News from 2007 to 2012 and managing editor from 2014 to 2017.

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