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Friday, June 28, 2013

Celestial Commentary

This week's blog post comes from collections intern Jay Bilinsky and is out of this world (literally).
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With the recent cosmic events of the summer solstice (which occurred on June 21st) and the hyped-up “supermoon” (June 23rd), people have the cosmos on their minds. As such, it’s a good opportunity to highlight some of the astronomical and cosmological texts here at the Rosenbach. Our collection of scientific texts is decidedly small; still, there are some gems on the topic of astronomy in the collection (old, vellum-bound gems!).

Before I get ahead of myself, I would like to take a moment to explain the significance of the “supermoon” phenomenon. Supermoon occurs when the moon is simultaneously full and at the closest point in its orbit around the Earth, which happens every 14 months or so. It is significant because during this time, the moon appears to be somewhat larger and substantially brighter than usual. The orbit of the moon is in the shape of an ellipse, coming to its closest point in orbit (perigee) at one time and coming to its furthest point (apogee) at the opposite side of the ellipse. In order for the moon to be full, it must be in “opposition” to the sun, meaning that the sun, Earth, and moon line up in that order. Check out the diagram from Cosmographia Apiani to see what I mean.
Cosmographia Petri Apiani, 1545. Rosenbach Museum & Library. A 545c Page 50. The cycles of the moon are shown, as viewed from Earth. Note that the bottom-most circle shows the moon in opposition to the sun.
The oldest scientific texts in the Rosenbach collection are written in Latin, which was once the language of scholars. Although this old Cosmographia text may preclude readers not versed in Latin, it contains many charts, diagrams, and fancy volvelles (free-spinning paper disks affixed with string). These models all give a sense of how much the science of astronomy expanded during the Renaissance. Petrus Apianus, the author of this particular Cosmographia, was an esteemed German scientist whose lushly illustrated books helped popularize the science of astronomy.
Cosmographia Petri Apiani, 1545. Rosenbach Museum & Library. A 545c Page 49. This volvelle (shown twice with the dial in different positions) predicts cycles of the moon according to date and time. Although no longer accurate, the wheels still spin with ease.
Although people have only become interested in supermoon phenomena in recent years, a similar cosmic event has interested people for thousands of years: eclipses. There are two kinds of eclipses: solar and lunar. Solar eclipses occur when the moon blocks our view of the sun. These are more common than lunar eclipses, but can only be seen from certain places on Earth. A lunar eclipse occurs when the moon passes through the Earth’s shadow. Lunar eclipses and supermoons are similar in that both can only occur when the moon is full. Books in the Rosenbach’s collections show that eclipses have been well understood for centuries. Information about eclipses can be found in very expected places in our collection, such as our astronomy books and almanacs, as well as some surprising spots, like our medieval belt book. A book titled Time’s Telescope by Duncan Campbell not only describes eclipses, but also accurately predicts them from the time of its publishing in 1734 to 1763.
“A Type of the Moon’s Eclipse." Time’s Telescope, 1734. Rosenbach Museum & Library. Holford 99. Page 96. This illustration depicts a lunar eclipse. The earth and moon are shown to have circular orbits, although this is just for simplicity’s sake; Campbell well understood the elliptical motion of these celestial bodies.

I hope that this post has demystified some of the mysteries of Earth’s moon. To see these historic scientific texts and more, make an appointment at the Rosenbach’s reading room. Finally, I leave you with a nice illustration from the Cosmographia showing eclipses of the sun in the 16th century. Enjoy, keep your eyes out for lunar eclipses, and never look directly at solar eclipses!
Cosmographia Petri Apiani, 1545. Rosenbach Museum & Library. A 545c. Page 13. Illustrations plotting past solar eclipses and projecting future solar eclipses, from 1542 to 1573. Full eclipses as well as partial (when the moon only obstructs part of the sun) are shown.

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Jay Bilinsky is a collections intern and a recent graduate of the Tyler School of Art at Temple University. He was drawn to the Rosenbach by its unique collections and fine art.

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