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by John Q McDonald --- 10 May 2017

Kepler's Somnium

The Dream, or Posthumous Work on Lunar Astronomy

translated, with a commentary by Edward Rosen

Johannes Kepler was a mathematician and astronomer who flourished around the turn of the 17th century. He was obsessed with the notion that planetary motions and positions were governed by the perfect Platonic solids. That geometry was the very language of God, and only perfect geometry could describe the natural world. While enduring the challenges of living as a Lutheran during the Catholic Counter-Reformation that tore through Eastern Europe, Kepler hammered away at his theories, attempting to build upon the Copernican Sun-centered universe. After long labors, he finally realized that, rather than rest upon rigid Platonic solids, the universe rather preferred to move in the graceful arcs of elipses (and other conic sections). This was a eureka! moment that ultimately led to Kepler's three laws of planetary motion. These are the foundation of celestial physics, keeping everything in their orbits, from satellites around the Earth to galaxies around each other. Kepler, himself, though, clung to the Platonic solids until his death in 1630.

Along the way, Kepler was forced to defend the Copernican view of the universe. Even astronomical greats such as Tycho Brahe tried to find ways to explain the motions of the planets without moving the Earth from the center of creation. One argument often used by the less scientifically sophisticated was, if the Earth were indeed moving (as we know now to be at 30 km/sec), then why do we not experience that motion? The Earth feels pretty solid and unmoving, after all. Kepler explained this by writing this short tale of a journey to the Moon. Often described as the first science fiction story, Kepler's work shows us a fantastical journey on the backs of demons to the surface of the Moon. He then describes the astronomical phenomena as seen from there, from the point of view of the Privolvan and Subvolvan inhabitants He demonstrates that, from the Moon, the Earth indeed appears to be moving in complicated ways, that it is all a matter of perspective. He came up with the idea while still a young graduate, worked on it from time to time throughout his life, but left it to his son to complete and publish. Indeed, it feels somewhat truncated, and the reader wants to know more about how Kepler imagined the beings of the Moon, Privolvans and Subvolvans, would live their lives.

Never one to really finish a work, Kepler supplemented this 30-page story with over two hundred footnotes, explaining various phenomena and giving sometimes lengthy clarifications of background, theory, politics and culture. The editor and translator of this book (first published in 1967), Edward Rosen, in turn, provides 399 footnotes to those footnotes, with modern clarifications and historical context to Kepler's long notations. And there are twelve appendices. What results here is a dense academic work of a couple hundred pages, in which Kepler's science-fiction story rests like a pearl deep within a giant shell. One needs to read Somnium through first, then return to peruse the notes upon notes upon notes. The result is a complex web of ideas that reveal, at least on this one point, the intellectual workings of one of the founders of modern astrophysics. And, while Kepler's notes clarify points made in the small text, they just as often further obfuscate the theoretical notions contained within. For example, he goes on at great length in describing geometrical details of the lunar day and night, with much confusing detail that might have benefited from pages of illustration. Rosen's own notes on the notes could have used more astronomical clarification, as well, including commentary on how Kepler's ideas are reflected in modern astronomy. The appendices offer historical and biographical context, documenting key figures who had a hand in The Dream and some of Kepler's scientific assumptions. We get a glimpse into the development in his thinking, especially in response to the observations of both Tycho and Galileo (i.e. Kepler's remarkably sci-fi explanation for lunar craters, first seen in detail with Galileo's telescope). But the present volume is more a work of intellectual and academic history than a history of science. Casual readers may find the notations on historical documents a bit heavy going and lack of relation to modern scientific understanding a bit befuddling. But the work is more than mere intellectual curiosity. Kepler's laws would surely have been discovered sometime. This was the period of enlightenment, after all. But Kepler was the first, and without him, there wouldn't today be the footprints of twelve humans on the Moon.

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See Also: [Kepler by John Banville] [Kepler Planet-discovering Spacecraft]

[Other books about Science]