Imagine yourself as one of your ancestors, say ten thousand years ago. Your reality
consists of a few tools, household utensils, perhaps buildings (the city-states were beginning
to appear along the Tigris) and, of course, all
that nature has to offer: trees, hills, plants, rivers,
streams—and the sky.
The sky is the biggest, greatest, most spectacular object
you know. During the day, the sky is crossed by
a brightly glowing disk from which all light and
warmth emanate. Announced in the predawn hours
by a pink glow on the eastern horizon, the great disk
rises, then arcs across the sky, deepening toward twilight
into a ruddy hue before slipping below the horizon
to the west. Without electric power, your working
hours are dictated by the presence of the sun’s light.
Flat Earth, Big Bowl
As the sun’s glow fades and your eyes become accustomed
to the night, the sky gradually fills with stars.
Thousands of them shimmer blue, silvery white, some
gold, some reddish, seemingly set into a great dark
bowl, the celestial sphere, overarching the flat earth
on which you stand.
Thousands of stars in the night sky?
Maybe that number has brought you back through a
starlit ten thousand years and into the incandescent
lamp light of your living room or kitchen or bedroom
or wherever you are reading this: “I’ve never seen
thousands of stars!” you protest.
We said earlier that, from many locations, our sky is
spoiled. The sad fact is that, these days, fewer and
fewer of us can see anything like the three thousand
or so stars that should be visible to the naked eye on a
clear evening. Ten thousand years ago, the night sky
was not lit up with the light pollution of so many
sources of artificial illumination. Unless you sail far
out to sea or travel to the high, dry desert of the
Southwest, you might go through your entire life
without really seeing the night sky, at least not the
way our ancestors saw it.
Man in the Moon
Even in our smog- and light-polluted skies, however, the Moon shines bright and
clear. Unlike the Sun, which appears uniform, the surface of the Moon has details we
can see, even without a telescope. Even now, some three decades after human beings
walked, skipped, and jumped on the Moon and even hit a golf ball across the lunar
surface, the Moon holds wonder. Bathed in its silver glow, we may feel a connection
with our ancestors of 10 millennia ago. Like them, we see in the lunar blotches the
face of the “Man in the Moon.”
If the face of the Moon presented a puzzle to our ancestors, they were also fascinated
by the way the Moon apparently changed shape. One night, the Moon might be
invisible (a new moon); then, night by night, it
would appear to grow (wax), becoming a crescent;
and, by one week later, be a quarter moon (which
is a half moon in shape).
Through the following
week, the Moon would continue to wax, entering
its gibbous phase, in which more than half of the
lunar disk was seen. Finally, two weeks after the
new moon, all of the lunar disk would be visible:
The full moon would rise majestically at sunset.
Then, through the next two weeks, the Moon
would appear to shrink (wane) night after night,
passing back through the gibbous, quarter, and
crescent phases, until it became again the all-butinvisible
new moon.
The cycle takes a little more than 29 days, a month, give or take, and it should be no
surprise that the word “month” derived from the word “moon.” In fact, just as our
ancestors learned to tell the time of day from the position of the Sun, so they measured
what we call weeks and months by the lunar phases. The lunar calendar is of
particular importance in many world religions, including Judaism and Islam. For
those who came before us, the sky was more than something to marvel at. It could
also be used to guide and coordinate human activity.
Lights and Wanderers
Ten thousand years ago, family time at night was
not occupied with primetime sitcoms followed by
the news and David Letterman. Our ancestors were
not glued to television screens, but presumably to
the free show above, the celestial sphere. Early cultures
noticed that the bowl above them rotated
from east to west.
They concluded that what they
were seeing was the celestial sphere—which contained
the stars—rotating, and not the individual
stars. All the stars, they noticed, moved together,
their positions relative to one another remaining
unchanged. (That the stars “move” because of
Earth’s rotation was a concept that lay far in the
future.)
The coordinated movement of the stars was in dramatic
contrast to something else the ancient sky
watchers noticed. While the vast majority of stars
were clearly fixed in the rotating celestial sphere, a
few—the ancients counted five—seemed to meander
independently, yet regularly, across the celestial
sphere. The Greeks called these five objects planetes,
“wanderers,” and, like nonconformists in an
otherwise orderly society, the wanderers would
eventually cause trouble. Their existence would
bring the entire heavenly status quo into question
and, ultimately, the whole celestial sphere would
come crashing down.
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