Date: October 18, 2009

Title: Geometry vs. Lunacy


Podcaster: Mark Thompson

Organization: Galileo 1610 –

Description: Galileo’s Earliest Telescopic Observations of the Moon

Bio: Mark Thompson, a professional cantor and amateur astronomer, has appeared as Galileo on radio, at community theatres and libraries, public schools, colleges and universities throughout the country. He has performed as Galileo for civic organizations, astronomy association conventions, marketing and outreach programs as well as private events and parties since 1996.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Brian Engler with thanks to everyone who has made this podcast possible, but especially to Dr. Pamela Gay, who has taught me much about the wonders of astronomy through her own podcast, and the multi-talented George Hrab, who never ceases to entertain me with his.


Geometry vs. Lunacy – Galileo’s Earliest Telescopic Observations of the Moon

What was the state of the Moon before Galileo assaulted it with his crude perspicillum?

For at least eighteen centuries it was regarded as pure and perfectly rotund, free of blemish, encased for all time in an immaculate crystalline sphere just like Aristotle had said. And this conception fit perfectly with recent Church doctrine, depicted iconographically as the Immaculate Conception, drawn from Revelation 12, verses 1-2, showing a pregnant woman with a crown of twelve stars standing on a crescent Moon, its smooth and translucent horns pointed downward toward the corrupted sublunar Earthly realm.

Then along came Galileo, fresh from his heady and victorious demonstration with his new and improved telescope to the Venetian Senate from the top of the campanile in St. Mark’s Square in August ‘09, and with one fell swoop he destroyed nearly two millennia of reality. With his artist’s brush he fashioned the moon into an entirely different creature: Earth like – rough, maculate, opaque – not made of some fifth element of the heavens, but of the same solid stuff as the Earth, illuminated not only by the Sun, but by the secondary light of the Earth as well.

This was not the first time someone had suggested that the moon was like the Earth. Some had even speculated that the Moon had always been inhabited. Even the great Kepler proposed that lunar residents could be dwelling in caves, which they constructed to shelter themselves from the scorching Sun. Others insisted they saw rain clouds on the Moon.

Galileo would have none of this lunacy. As early as 1604, five years before he used his telescope to begin demolishing the Aristotelian theory of the heavens, Galileo already had a mathematician’s view of our closest neighbor.

In the Considerations of Alimberto Mauri, a controversial work on the new star of 1604 published pseudonymously in 1606, Galileo had noted the irregularity of the terminator at quadrature as evidence that the Moon has large mountains and flat planes.

“But since everything has its proper cause, I shall proceed with this investigation reasoning differently, and I shall say that the moon, according to Posidonius and other ancient Philosophers (as Macrobius repeats) is so similar to the earth as to be called by them another earth. Then it is not inconsistent to think that it is likewise not entirely even, but that there are also on the moon mountains of gigantic size, just as on earth; or rather, much greater, since they are [even] sensible to us. For from these, and from nothing else, there arise in the moon scabby little darknesses, because greatly curved mountains (as Perspectivists teach) cannot receive and reflect the light of the sun as does the rest of the moon, flat and smooth. And for proof of this I shall adduce an easy and pretty observation that can be made continually when she is in quadrature with respect to the sun; for then the semicircle is not smooth and clean, but always has a certain boss in the middle. For this, what more probable cause will ever be adduced than the curvature of those mountains? By that, and particularly in that [middle] place, she comes to lose her perfect rotundity.”

But what proof did this mere mathematician have? What unmitigated nerve!

Then, there is the matter of the dating and provenance of Galileo’s earliest drawings of the 5-day old Moon that appear in Galileo’s Starry Messenger, published in March of 1610. What controversy these drawings have inspired amongst Galilean scholars! According to a study by Professor Righini in 1974, Galileo may have begun sketching the Moon’s surface as early as the first week in October, 1609, only a few short weeks after he first devised and gifted his 8-power spyglass to the Doge of Venice. In that case, he must have already been using a superior instrument; after all, no self-respecting telescope enthusiast would just give away the most powerful weapon from his arsenal, certainly not Galileo who was always looking to one-up the next guy and claim first prize when it came to his discoveries. This is the reason I strongly doubt Stillman Drake’s contention that Galileo didn’t even bother looking at the Moon through his telescope until the end of November or early December, 1609. With all due respect to the late, great Mr. Drake whose research is unequaled by any modern Galilean scholar — are you kidding, Sir? Galileo would have been dying to look at the Moon through an even more powerful lens system to confirm what he had already predicted back in his 1604: the Moon had these “scabby little darknesses” that reflected the light of the Sun at a certain angle, which with simple trigonometry, one could easily calculate the height of the lunar mountains.

Which brings one finally to wonder why Galileo deliberately distorted the size and shape of one particular crater which reminded him of “the Province of Bohemia, near the middle of the Moon” commonly supposed to be “Albategnius,” when he exaggerated it beyond all respectable size and proportion in his drawing. Lunacy? No. Neither Galileo’s fabricated lens nor his God-given lens had failed him, nor was his trying to misrepresent what he saw in order to delude the unenlightened. This mathematician-turned-artist was merely trying to visually demonstrate the irregularities of the lunar surface in situ, a style which Professors Van Helden and Biagioli have identified as disegno, a popular representational technique in which he was well-trained and that he judiciously employed in order to clearly communicate his revolutionary discoveries.

End of podcast:

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