Sky & Telescope - February 2020 - 67

K EPLER SPACECR A F T L AUNCH: N ASA / K IM SHIFLE T T; E A RTH A ND
M OON FRO M G A LILEO PROBE: N ASA / JPL / ASU

u The Kepler spacecraft, shown here launching
in 2009, discovered more than 2,600 exoplanets
in its nine-year lifespan. Carl Sagan, among others, insisted on naming it after the great 17thcentury advocate for exploring alien worlds.

the very evidence that locked her away.
He assumed a responsibility that was
never his and was plagued by guilt for
the rest of his life.
When Kepler returned to Somnium,
he set out to dispel the misrepresentation of his work and mischaracterization of his mother. Accordingly, he
supplemented the manuscript with
footnotes containing elucidations of lunar geography, discussions of telescopic observations, and rebukes of those who
(he believed) had weaponized his words against an innocent
woman. The remarks - 223 in all - are many times longer
than the main text, and required a decade to complete.
Kepler's Somnium was a lifelong exercise in scientiﬁc investigation, imagination, and patience. But illness struck Kepler
down before the manuscript made it to print. His son Ludwig
took charge of the manuscript, which was ﬁnally published in
1634, four years after Kepler's death.
Combining a mystical framework, a weak narrative, and
a profound but rambling scientiﬁc treatise, Somnium is not
an easy read. While the book had a deep effect on some of
Kepler's contemporaries (see the discussion on the facing
page), others were confused, and most were probably unaware
of its existence. Not until the mid-20th century was Somnium
studied in earnest. We now recognize it as the ﬁrst modern
contemplation on lunar geography and spaceﬂight.
A far cry from the doctoral dissertation from which it
sprang, the completed Somnium is more than an effort to
promote and popularize the Sun-centered universe. It's a
prophecy about the potential of science and the promise of
our species. Kepler believed that space travel was indeed possible, that someday humanity would construct ships suited to
the cosmic seas and sail for uncharted worlds.
More than three centuries elapsed after Kepler's death
before humans attained spaceﬂight - before they propelled
themselves into the heavens, braving that dangerous expanse,
destined for the Moon. Then, far from home, those voyagers
beheld Earth from aloft - its lands adorned by vibrant hues,
its oceans peeking through wispy clouds - and darkness
stretching in every direction. But marooned in a time long
past, Kepler was never to know of humanity's rendezvous
with the Moon and the bootprints impressed in its surface.
While our capabilities and technologies far surpass those
of Kepler's time, our fundamental situation remains the
same. We reckon with the blank regions on our maps - all
that lies outside our line of sight and beyond our reach. We
stare out at the universe through a pinhole, fated to know
hardly any of it - just our little corner, perhaps, and a few
remote fragments, here and there. We try mightily to force

a retreat of the boundary separating
knowledge and ignorance. Yet when we
cross one frontier, we discover a new
one. So we do what we can, in the time
we have, to light up the darkness in
which we live, and bequeath a universe a
little less unknown.
Each generation that follows us will
gaze up with wide eyes and see the
universe for the ﬁrst time. Our successors will access perspectives yet unseen,
behold wonders yet unimagined, and
reveal the cosmos as it has never been
known to us nor any human before. And
we, islanded in our own time, reach into theirs, helping to
create a future that we cannot live to experience directly.
Space travel is an endeavor owed to the labor of multitudes - to the generations past who developed the technology
and garnered the scientiﬁc know-how to propel us into the
universe. Now, the time is ours to carry on this remarkable
undertaking. Today, it is we, the most recent iteration of
humankind, who make the unthinkable plausible and the
extraordinary commonplace. We are the next chapter in a
story far greater than ourselves - a story spanning from the
distant past to distant worlds. With every voyage beyond
Earth, we fulﬁll the dreams of our ancestors and set the stage
for our descendants to venture farther than we ever will.

¢ JAKE ROSENTHAL is an aerospace engineer at NASA's
Goddard Space Flight Center. He was born a quarter-century
too late to witness humankind's first "giant leap," but at the
right time to take part in the next.
FURTHER READING: The standard English translation of Kepler's Somnium, with ample commentary, is by Edward Rosen,
Dover Publications, 2003. Marjorie Hope Nicolson's Voyages to the
Moon (Macmillan Co., 1948), sadly long out of print, is a superb
synopsis of spaceflight stories from ancient Greece to the first balloon flight in 1783.

After a gravity assist
in 1992, NASA's
Galileo probe
photographed Earth
and the Moon as it
sped on to its 1995
rendezvous with
Jupiter.

sk yandtelescope.com * FEBRUARY 2 02 0

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Sky & Telescope - February 2020

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