Science in the Bluegrass — Art, science and history in St. Rose Church

A portion of the stained glass window at St. Rose Church, a few miles outside of Springfield, Ky. (Photo Special to The Record)

Chris Graney

See interesting art, science and history here in the Archdiocese of Louisville! 

St. Rose Church, a few miles outside of Springfield, Ky., is the original Dominican church in the United States, established in 1806.

English Dominicans, spearheaded by Edward Fenwick, founded St. Rose. Bishop John Carroll (who in 1789 became the first U.S. bishop — of Baltimore) offered to let the Dominicans, who were looking to come to the U.S., set up shop in Kentucky. It is possible that Carroll sent them to Kentucky to make sure that they were not in competition with the Jesuits at Georgetown in Maryland.

The art-science-history is in one of St. Rose’s stained glass windows. The window depicts Jesus crowning Mary as Queen of Heaven. It includes both a crescent moon and stars. 

The window’s moon is particularly interesting. When our moon is crescent, we can often see not only the bright crescent but also rest of the moon, much more dimly. The artist who made the window shows these two levels of lunar illumination — which in times past were called the “primary” and “secondary” lunar lights — in remarkable fashion.

The window shows the moon casting rays in all directions. However, the artist specifically depicts the rays emanating from the larger and dimmer portion of the moon as darker than those emanating from the crescent. The artwork seems to emphasize that the dimmer portion of the moon indeed gives off light, just less intensely.

A close up of St. Rose’s stained glass window depicts both a crescent moon and stars. The artist who made the window shows two levels of lunar illumination — which in times past were called the “primary” and “secondary” lunar lights. (Photo Special to The Record)

What is more, the artist also illustrates some of the interesting properties of this “secondary light.” The secondary light is often seen to be more intense on the side of the moon opposite the bright crescent; in fact, observers will see that opposite edge as having a distinct glow. The St. Rose Coronation Window displays all this. In the window, the dim side of the moon clearly brightens with increasing distance from the crescent, and there is a very distinct edge glow.

There is interesting history here. Galileo, after observing the moon with the newly-invented telescope, had argued in his groundbreaking 1610 book “Starry Messenger” that the secondary lunar light is of Earth; the sun illuminates the bright crescent, but the Earth illuminates the rest.  Moon and Earth therefore light up each other, he explained.

Traditional ideas said that heavenly bodies like the moon have nothing in common with Earth.  They are their own realm, and the moon glows with heavenly light only, not Earthly light.  

The Jesuit astronomer Father Christoph Scheiner and his student, Johann Georg Locher, argued against Galileo in their 1614 book “Mathematical Disquisitions.” The moon’s edge glow showed that the moon was mildly translucent, they said. They thought the secondary light came from sunlight penetrating through the moon.  Balls of translucent crystal showed the same behavior, they said.  

Today we know Galileo was right. The moon is not a mildly translucent crystal! The secondary light is now called “Earthshine.” 

People who observe the moon, especially with telescopes, see it. They often sketch it. Father Scheiner and Locher’s arguments would have had real weight, because they are “reproducible.” Perceptive people could see and record for themselves what they were describing — people like the St. Rose window artist (who seems to have used a telescope enough to be familiar with the edge glow phenomenon). 

Yet the edge glow cannot be photographed. It seems to be a real illusion of the eyes, not a real glow. It is not fully understood, but it has recently been discussed by Bob King at “Sky & Telescope” magazine. (Online, search his name and “solving an earthshine mystery.”) 

Of course I sent him a picture of the window of St. Rose.

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