50 PART 1^ |^ EXPLORING THE SKY
How you would burst out laughing, my
dear Kepler, if you would hear what the
greatest philosopher of the Gymnasium told
the Grand Duke about me...
— FROM A LETTER BY GALILEO GALILEIA
bout four centuries ago, Galileo was condemned
by the Inquisition for his part in a huge controversy
over the nature of the universe, a controversy that
focused on two problems. Th e place of the Earth was the most
acrimonious issue; was it the center of the universe or was the
sun at the center? A related issue was the nature of planetary
motion. Ancient astronomers could see the sun, moon, and
planets moving along the ecliptic, but they couldn’t describe
those motions precisely. To solve the fi rst problem of the place
of the Earth, astronomers also had to solve the second problem
of planetary motion.
The Roots
of AstronomyAstronomy has its origin in a noble human trait, curiosity. Just
as modern children ask their parents what the stars are and why
the moon changes, so did ancient humans ask themselves those
same questions. Th eir answers, often couched in mythical or reli-
gious terms, reveal great reverence for the order of the heavens.
Archaeoastronomy
Most of the history of astronomy is lost forever. You can’t go to
a library or search the Internet to fi nd out what the fi rst astrono-
mers thought about their world because they left no written
record. Th e study of the astronomy of ancient peoples has been
called archaeoastronomy, and it clearly shows that trying to
understand the heavens is part of human nature.
Perhaps the best-known example of archaeoastronomy is
also a huge tourist attraction. Stonehenge, standing on Salisbury
Plain in southern England, was built in stages from about 3000
bc to about 1800 bc, a period extending from the late Stone Age
into the Bronze Age. Th ough the public is most familiar with the
monument’s massive stones, they were added late in its history.
In its fi rst stages, Stonehenge consisted of a circular ditch slightly
larger in diameter than the length of a football fi eld, with a con-
centric bank just inside the ditch and a long avenue leading away
toward the northeast. A massive stone, the Heelstone, stood
then, as it does now, outside the ditch in the opening of the
avenue.
4-1
As early as ad 1740, the English scholar W. Stukely sug-
gested that the avenue pointed toward the rising sun at the
summer solstice, but few historians accepted that it was inten-
tional. Nevertheless, seen from the center of the monument,
the summer solstice sun does rise behind the Heelstone. More
recently, astronomers have recognized other signifi cant astro-
nomical alignments at Stonehenge. For example, sight lines
point toward the most northerly and most southerly risings of
the moon (■ Figure 4-1).
Th e signifi cance of these alignments has been debated.
Some have claimed that the Stone Age people who built
Stonehenge were using it as a device to predict lunar eclipses.
After studying eclipse prediction in the previous chapter, you
understand that predicting eclipses is easier than most people
assume, so perhaps it was used in that way, but the truth may
never be known. Th e builders of Stonehenge had no written
language and left no records of their intentions. Nevertheless,
the presence of solar and lunar alignments at Stonehenge and at
many other Stone Age monuments dotting England and conti-
nental Europe shows that so-called primitive peoples were pay-
ing close attention to the sky. Th e roots of astronomy lie not in
sophisticated science and logic but in human curiosity and
wonder.
Astronomical alignments in sacred structures are common
all around the world. For example, many tombs are oriented
toward the rising sun, and Newgrange, a 5000-year-old passage-
grave in Ireland (■ Figure 4-2), faces southeast so that, at dawn
on the day of the winter solstice, light from the rising sun shines
into its long passageway and illuminates the central chamber.
No one today knows what the alignment meant to the builders
of Newgrange, and many experts doubt that it was actually
intended to be a tomb. Whatever its original purpose, Newgrange
is clearly a sacred site linked by its alignment to the order and
power of the sky.
Building astronomical alignments into structures gives them
meaning by connecting them with the heavens. Navajo Indians
of the American southwest, for example, have for centuries built
their hogans with the door facing east so they can greet the rising
sun each morning with prayers and off erings.
Some alignments may have served calendrical purposes. Th e
2000-year-old Temple of Isis in Dendera, Egypt, was build to
align with the rising point of the bright star Sirius. Th e fi rst
appearance of this star in the dawn twilight marked the fl ooding
of the Nile, so it was an important calendrical indicator. Th e link
between Sirius and the Nile was described in Egyptian mythol-
ogy; the goddess Isis was associated with the star Sirius, and her
husband, Osiris, was linked to the constellation you know as
Orion and also to the Nile, the source of Egypt’s agricultural
fertility.
An intriguing American site in New Mexico known as the
Sun Dagger unfortunately has no surviving mythology to tell its