Sky & Telescope - February 2020 - 64

Transgenerational Spaceflight

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While Johannes Kepler was working on the ﬁrst version
of Somnium, his great contemporary Galileo Galilei heard
of a new device that made distant objects appear bigger.
Galileo built his own telescope (as we now call it), turned
it to the night sky, and in one year he discovered that the
Milky Way comprises innumerable faint stars, conﬁrmed
Petrarch's theory of complex lunar topography as shown
in the sketches on the facing page, discovered Jupiter's
four bright moons, and observed their changing patterns.
That was a severe blow to the geocentric theory, because
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FEBRUARY 2 02 0 * SK Y & TELESCOPE

t The title page of Somnium reads as follows: "By Joh.
Kepler, formerly Imperial Mathematician, Somnium, or
Posthumous Work on Lunar Astronomy," followed by
publication information.

Kepler speculated that space is permeated
with a deadly barrage of solar radiation. Therefore, Moon ﬂights must be scheduled for a lunar
eclipse, when Earth is situated between the Sun
and Moon, generating a shroud of darkness in
which the voyagers ﬁnd safe passage.
The rigors of launch are compared to the
detonation of explosives. The ascent so jars the
explorer that he requires sedation. His body
must be fastened and protected, lest his limbs be horriﬁcally torn away. But at the end of this torturous episode, the
explorer coasts peacefully to the Moon without any further
application of force.
A close inspection of the Moon reveals perilous terrain.
Here, Kepler indulges in what he called lunar geography.
In Somnium, he describes the Moon's features as dwarﬁng
those of Earth. Mountains tower above all earthly peaks, and
chasms plummet to depths far below the greatest terrestrial
trenches. The climate is no more tame. Each day and night on
the Moon causes huge swings in temperature, blistering heat
giving way to severe cold.
In time, Kepler proved correct in his assessment of the
climate; however, he was wrong about the size of lunar
mountains and many other matters, including the presence
of life. Kepler populated the lunar landscape with a diverse
community of bizarre creatures. He even included a detailed
description of how intelligent beings might have built the

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it proved that at least four objects orbit something other
than Earth! He published these results in 1610 in a short
pamphlet entitled Sidereus nuncius (Starry Message or
Messenger) that electriﬁed the scientiﬁc community.
Kepler was thrilled by the pamphlet. He wrote an
open letter to Galileo titled Conversation with the Starry
Messenger that discusses the new revelations in detail.
Toward the end, he mentions the possibility that both
the Moon and Jupiter are inhabited and proceeds to say,
"But as soon as somebody demonstrates the art of ﬂying,

SOMNIUM TITLE PAG E: LIBR A RY OF CONG RESS

imagined what someone would experience if
uprooted from our planet and planted on the
lunar surface: The motions of the Moon go
undetected, while those of Earth are revealed.
Kepler's dissertation challenged the prevailing Earth-centered model of the universe, and
unfortunately for him, the professor in charge
of dissertations was deeply entrenched in the
geocentric worldview. Typically, a dissertation
would have been the subject of public debate,
but Kepler's writing was denied an audience.
Wary of protesting this ruling, Kepler fell silent
on the matter. He shelved the work, awaiting a
time when circumstances would swing in his favor.
When Kepler returned to the dissertation 16 years later,
he decided to reframe it as a dream. He believed that in this
context, geocentrists could dismiss objectionable material as
inventions of his imagination. Thus, if portrayed as ﬁction,
his thoughts on astronomy might evade censorship.
During this period of revision, Kepler also introduced a
passage that addresses lunar ﬂight itself. In telling this stage of
the journey, he harks back to the ancient Greeks, with whom
literary voyages beyond Earth originated. The stories of antiquity were facetious in their treatment of space travel, recounting humans being lofted into the heavens by whirlwinds or
transported across space by gods (see the boxed text on the
previous page). Kepler follows this precedent; his explorers
require the services of a spirit to convey them between worlds.
However, amidst this homage to the ancients, Kepler breaks
new ground with an earnest discussion of the practical problems of spaceﬂight.

Sky & Telescope - February 2020

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