12
T
hroughout history, the aim
of astronomy has been to
make sense of the universe.
In the ancient world, astronomers
puzzled over how and why the
planets moved against the backdrop
of the starry sky, the meaning of
the mysterious apparition of comets,
and the seeming remoteness of
the sun and stars. Today, the
emphasis has changed to new
questions concerning how the
universe began, what it is made
of, and how it has changed. The
way in which its constituents, such
as galaxies, stars, and planets, fit
into the larger picture and whether
there is life beyond Earth are some
of the questions humans still
endeavor to answer.
Understanding astronomy
The baffling cosmic questions of
the day have always inspired big
ideas to answer them. They have
stimulated curious and creative
minds for millennia, resulting in
pioneering advances in philosophy,
mathematics, technology, and
observation techniques. Just
when one fresh breakthrough
seems to explain gravitational
waves, another discovery throws
up a new conundrum. For all we
have learned about the universe’s
familiar constituents, as seen
through telescopes and detectors
of various kinds, one of our biggest
discoveries is what we do not
understand at all: more than 95
percent of the substance of the
universe is in the form of “dark
matter” and “dark energy.”The origins of astronomy
In many of the world’s most
populated areas today, many of us
are barely aware of the night sky.
We cannot see it because the blaze
of artificial lighting overwhelms
the faint and delicate light of the
stars. Light pollution on this scale
has exploded since the mid-20th
century. In past times, the starry
patterns of the sky, the phases of
the moon, and the meanderings
of the planets were a familiar
part of daily experience and a
perpetual source of wonder.
Few people fail to be moved the
first time they experience a clear
sky on a truly dark night, in which
the magnificent sweep of the Milky
Way arches across the sky. Our
ancestors were driven by a mixture
of curiosity and awe in their search
for order and meaning in the great
vault of the sky above their heads.
The mystery and grandeur of the
heavens were explained by the
spiritual and divine. At the same
time, however, the orderliness andpredictability of repetitive cycles
had vital practical applications
in marking the passage of time.
Archaeology provides abundant
evidence that, even in prehistoric
times, astronomical phenomena
were a cultural resource for societies
around the world. Where there is
no written record, we can only
speculate as to the knowledge
and beliefs early societies held.
The oldest astronomical records
to survive in written form come
from Mesopotamia, the region
that was between and around the
valleys of the Tigris and Euphrates
rivers, in present-day Iraq and
neighboring countries. Clay tablets
inscribed with astronomical
information date back to aboutINTRODUCTION
Philosophy is written in
this grand book, the universe,
which stands continually
open to our gaze.
Galileo Galilei