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.