Brian (digibri) wrote,
Brian
digibri

Visions of Ancient Night Sky Were Hiding in Plain Sight for Centu ries

This is a fascinating little story about a researcher who decided to look a
bit closer. It's definately worth a read.

B.


Visions of Ancient Night Sky
Were Hiding in Plain Sight for Centuries

By KENNETH CHANG
Published: January 18, 2005




SAN DIEGO, Jan. 12 - Two thousand years later, astronomers still talk about
Hipparchus' star catalog, the earliest known compendium of the night sky.

Hipparchus, who lived in Greece during the second century B.C., was perhaps
the world's first great astronomer. He calculated, within six and a half
minutes, the length of a year. He figured out that Earth's axis wobbles as
it spins. For his star catalog, completed in 129 B.C., he devised a
coordinate system to plot each star's location and a scale to rank the
brightness. Astronomers still use this magnitude scale today.

Most of Hipparchus' work, however, is known only secondhand. No one has seen
the catalog for centuries, a fabled ancient text apparently lost forever.

No one until Dr. Bradley E. Schaefer thought of looking for it on a statue.

At a meeting of the American Astronomical Society here, Dr. Schaefer, a
professor of physics at Louisiana State University, reported that the text
of Hipparchus' catalog was still lost, but that he had found possibly the
next best thing, a pictorial representation of the catalog's contents.

"Here we have a real example of lost ancient knowledge being discovered,"
Dr. Schaefer said. Perhaps not quite the da Vinci code, but, as he described
it, "some of the most influential lost ancient lore."

Dr. Owen Gingerich, an expert on the history of astronomy at Harvard,
described Dr. Schaefer's research as "quite astonishing."

Remarkably, the new discovery has been in plain view for centuries.

A seven-foot-tall statue at the National Archaeological Museum in Naples,
Italy, shows the god Atlas kneeling with a globe weighing on his shoulders.
Atlas was sentenced by Zeus to hold up the sky, and the globe is a depiction
of the night sky as seen from Earth, with pictures of Aries the ram, Cygnus
the swan, Hercules the hero and other animals and people representing 41
constellations. The statue, known as the Farnese Atlas, is the oldest
surviving pictorial record of Western constellations. It dates to Roman
times, around A.D. 150, and is known to be a copy of an earlier Greek work.

"It was just sitting there, waiting," Dr. Schaefer said.

Dr. Edwin C. Krupp, director of the Griffith Observatory in Los Angeles,
said modern notions tended to discount Greek myths as more astrology than
astronomy. "We tend to think they were silly stories that the ancients
told," he said. "I don't think anyone thought to take the Farnese Atlas
seriously as a source of ancient data."

The sculpture offers hints that it may have serious scientific
underpinnings. The globe has horizontal lines for the Equator, the Tropics
of Cancer and Capricorn, and the Arctic and Antarctic Circles. An angled
circle marks the ecliptic, the plane defined by the orbits of the planets,
and vertical lines mark colures, the equivalent of lines of longitude on a
map of the Earth.

Some historians had speculated that the sculptor might have consulted the
work of Ptolemy, who lived about 250 years after Hipparchus, or Aratus, who
described the constellations in a poem about a century before Hipparchus.
Curiously, no one appears to have suggested Hipparchus' catalog as the
reference source.

Dr. Schaefer asked a simple question: in what year were the constellations
in the positions depicted on the Farnese Atlas? Because of the wobble in the
Earth's axis, the constellations slide around the sky on a 26,000-year
cycle.

He noted where parts of constellations that correspond to specific stars
intersected with the lines on the globe. For example, the westernmost part
of Aries' horn, which corresponds to the star Gamma Ari, touches one of the
colures, and the chest of Leo, location of the star Regulus, lies on the
Tropic of Cancer line. From photographs he took of the statue during a
vacation stop in Naples last year, he calculated the positions of other
constellation stars.

"They tell you the time," Dr. Schaefer said. "It's like the big hand moving
through the sky."

Using 70 stars, Dr. Schaefer determined that the Farnese Atlas best matches
the sky of 125 B.C. give or take 55 years - too early for Ptolemy, too late
for Aratus, but almost a perfect match for Hipparchus. In addition, the
constellations were placed more accurately than could be deduced from verbal
descriptions, Dr. Schaefer said, another argument against Aratus' poem.

He also found that the Farnese Atlas globe agreed in detail with the only
surviving work of Hipparchus, a commentary on Aratus and Eudoxes, an earlier
astronomer who provided the basis for Aratus' poem. On the other hand, Dr.
Schaefer found contradictions between the globe and the writings of Aratus,
Eudoxes and Ptolemy.

Dr. Schaefer said Hipparchus made small celestial globes showing the
positions of stars in his catalog, and the original Greek sculptor probably
consulted one of these globes in chiseling the Farnese Atlas.

"This is a credible demonstration," Dr. Krupp said. "I think this is the
first time that a very detailed systematic and careful analysis of this has
been performed."

Now that astronomers and science historians seem to have a direct
representation of Hipparchus' catalog, they can try to figure out questions
like which coordinate system he used. It will also be fodder for a debate as
to who was the greater astronomer of antiquity, Hipparchus or Ptolemy?

Dr. Gingerich, who has considered himself in Ptolemy's camp, said, "Now I
may have to do some rethinking."

Some Hipparchus supporters even contend that Ptolemy created his star
catalog largely by plagiarizing Hipparchus.

Dr. Schaefer diplomatically said that they were both the greatest.
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