Sky & Telescope - October 2023 - 65

BOOK REVIEW by Cristina Montes
Dante on Astronomy
THE SUN AND THE OTHER STARS OF DANTE ALIGHIERI:
A Cosmographic Journey Through the Divina Commedia
Sperello di Serego Alighieri and
Massimo Capaccioli
World Scientific Publishing Co., 2022
180 pages, ISBN 978-981-124-549-7
US$58.00, hardcover
from where his journey began. (Dante
made himself a character in his own
story.) He imagined the different levels
of paradise to comprise the heavenly
bodies - the Sun, the Moon, and the
planets out to Saturn - revolving
around Earth along with the fixed stars.
The journey ended at the highest level
of paradise, the Empyrean, a heaven of
pure light lying beyond the stars at the
edge of the universe.
Despite living at a time when people
thought the Sun lay at the center of
the universe, and despite espousing the
medieval view that did not distinguish
astronomy from astrology (the authors
devote a chapter to this topic), Dante
actually got much of the science right.
For instance, in Purgatorio the poet
REFERENCES TO ASTRONOMY
abound in Dante Alighieri's The Divine
Comedy. Dante assumed his readers
understood them - people in his day
were more familiar with the skies than
we are today, in part because they had
to rely on the stars and their feeble light
for traveling at night. Sperello di Serego
Alighieri, an astrophysicist and direct
descendant of Dante (19th generation
after the poet), and Massimo Capaccioli,
a top Italian astronomer, wrote The
Sun and the Other Stars of Dante Alighieri
to explicate those astronomical references
within the context of the cosmological
knowledge of Dante's time.
Dante (1265-1321) set his fictional
journey through Hell, purgatory, and
paradise (the narrative poem's Inferno,
Purgatorio, and Paradiso) within an
Earth-centered cosmological model. He
located Hell at the core of our planet
and envisaged purgatory as a mountain
located on the opposite side of the globe
correctly attributes the appearance of
rainbows to refraction of solar rays in
raindrops: " And just as the air, when
it is very moist, becomes adorned with
various colors because it reflects another's
rays . . . " Dante also, in Paradiso,
accurately explains the tides: " And as
the turning of the heaven of the moon
covers and uncovers the shores without
pause, so Fortune does with Florence. "
Even when referring to the darkness
that the Gospels say fell as Christ
hung on the cross, Dante alluded to the
fact that solar eclipses happen during
new Moon rather than full Moon.
Hence, the twilight that scripture says
descended as Christ died - which
occurred during full Moon - was,
Dante claims in Paradiso, an extraordinary
phenomenon: " One says the Moon
turned back during Christ's passion and
interposed itself so that the light of the
Sun could not reach the Earth. "
The dialogue that Dante the character
has with Beatrice, his guide from the
end of Purgatorio through Paradiso, on
what created the " spots " on the Moon
serves as a masterful scientific treatise.
Beatrice corrects Dante's notion that
differences in density of lunar matter
cause the dark regions we now call
maria to stand out from lighter-colored
areas of the Moon. After walking Dante
through thought experiments (which
remind one of what Einstein did so
famously six centuries later), Beatrice
explains the causes of the Moon's color
differences. They arise, she says, from
the " virtue " that the Empyrean distributes
- in other words, from the different
degrees that various substances
reflect light. Indeed, as we know today,
the Moon's dark maria consist of basalt,
which reflects light less than the more
reflective anorthosite in the lunar
highlands.
The authors discuss the state of
astronomy before Dante as well as the
date and time in which The Divine Comedy
was set based on his descriptions
of the sky. They also delve into parallel
universes, the planets and stars, and the
mysteries of the Milky Way. Altogether
the book is a fascinating peek into the
state of medieval astronomy, which,
despite its errors, was more sophisticated
than we moderns give it credit for.
As such, the book is a valuable resource
on the history of astronomy.
The Sun and the Other Stars of Dante
Alighieri is somewhat technical, but
astronomy enthusiasts interested in
Dante, Dante enthusiasts curious about
astronomy, and anyone fascinated by
medieval astronomy will love the book.
¢ CRISTINA MONTES is an attorney, law
professor, and writer based in Manila,
the Philippines. Her Focal Point " From
Street to Streaming " ran in the July 2022
issue, p. 84.
sk yand tele scope .o r g * OCTOBER 2023 65
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Sky & Telescope - October 2023

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