The tabletop planetarium moved the Copernican revolution from the university into the homes of society's upper crust—a big step toward the eventual popularization of astronomy.
In the 1500s and 1600s, the new Sun-centered astronomy had been largely confined to learned treatises and university lectures. The notable exception was Galileo, who had necessarily concentrated on making plausible the motion of the Earth, because that was such an absurd notion at first hearing. Finally after 1700, clockmakers, who had the knowledge and tools to assemble precision gearworks, gave these new ideas material form and spread them into the upper layers of society. An elegant tabletop planetary machine allowed an Earl, or even a wealthy merchant or lawyer, to impress his friends with his knowledge of the latest ideas about the cosmos.
I take a professional interest in such matters because the Adler Planetarium has the first tabletop planetarium. It was made and signed by London clockmaker George Graham.
A tabletop planetarium that includes a planet spinning on a tilted axis, while traveling around the Sun, and a moon circling the planet, needs to have some pretty fancy machinery inside it. We call such a machine an "orrery", after the Earl of Orrery, an early patron of planetary machines. Contemporaries recorded that George Graham made two orreries, the first of their kind, while working in the London shop of Thomas Tompion, an older and more famous clockmaker. This fact lets us pin down the date of these two first orreries to sometime between 1704 and 1709, when Graham was working in Tompion's shop.
One of Graham's first orreries is now at the Adler Planetarium in Chicago. The second orrery also survives, and is now at the History of Science Museum in Oxford, England. Here is that other one:
This Oxford orrery is very nearly a twin of ours, down to the semicircular pass-through that lets the moon pass below a metal pointer directed from the Sun toward the Earth. (See the final photograph, below.) I'd like to point out, however, three ways in which the Oxford orrery is more finished than the one at the Adler. First, its wooden case is detailed in silver. Second, the little Earth globe on the machine at Oxford shows an outline map of the continents, an embellishment missing from the Earth globe on the Adler orrery. And lastly, the second, prestigious signature appears on the Oxford machine, that of big-name clockmaker Thomas Tompion.
It feels a little disloyal to argue that a significant object in our collection is inferior to a nearly-identical object at another museum. I confess to an ulterior motive. I believe that the Adler Planetarium orrery was the prototype—and thus the first of those first two orreries that George Graham made between 1704 and 1709, when he introduced the Copernican system to fashionable society. The lovely piece at Oxford was number two.
You will find these and other fascinating devices that embody our sense of cosmic wonder in our Planetary Machines exhibition, which runs through Monday, September 2.
Written by Bruce Stephenson, curator at the Adler Planetarium.