Copyright © 1997 The Seattle Times Company

Tuesday, June 17, 1997

Science: Conjuring constellations

by Alexandra Witze

Dallas Morning News

People see patterns everywhere - in clouds, in ink blots and in the stars scattered across the night sky.  Ink blots may be purely a 20th-century phenomenon, but the stars are not. For thousands of years, people have gazed skyward and discerned patterns - constellations - in the pinpoints of light.

Astronomers and historians wonder why many of the constellations of the Western world have remained the same for millennia. The Big Dipper, Orion and the constellations of the zodiac are ancient constructs, created when early civilizations were trying to make sense of the heavens. Of the 88 constellations recognized by astronomers today, at least 46 were described in star catalogs from thousands of years ago.

When, exactly, did people first form designs from the stars? Astronomers can't know for certain, because there are no ancient maps of the stars, only fragments of texts that hint at star patterns. So historians must piece together scraps of evidence with detailed calculations of ancient star positions to make their best guesses.

Now, a Russian astronomer-turned-historian thinks he may be able to explain when, where and how the first constellations were created. Alexander Gurshtein, vice director of Russia's Institute for the History of Science and Technology and a visiting scholar at Mesa State College in Grand Junction, Colo., believes that the earliest constellations may date back more than 16,000 years. According to Gurshtein, these constellations have endured through human history for so long because various civilizations over time have applied similar symbolic meanings to them. Other astronomers say Gurshtein's work is intriguing, though speculative.

"When you try to put yourself in the minds of people from thousands of years ago, you could make some pretty big mistakes," said Owen Gingerich, a historian of astronomy at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "The best you can hope for is a vague understanding of what they were thinking." Gurshtein has published popular descriptions of his work in the June issue of Sky & Telescope and the May/June issue of American Scientist magazine. Accounts of his research appear in the journal Vistas in Astronomy.

Some of the most controversial aspects of Gurshtein's work concern his theory on the origin of the zodiac, the 12 constellations that lie along the sun's path in the sky. (A 13th constellation along that path, Ophiuchus, is not considered part of the zodiac.)

Gurshtein thinks that the zodiacal constellations weren't sketched out all at once. Instead, he says the dozen constellations were defined over thousands of years in three sets of four constellations. Gurshtein says that a clue to understanding early constellations is taking into account the wobbling motion of Earth. As Earth spins on its axis, it wobbles like a top. Every 26,000 years, the axis of this earthly top traces a complete circle through the sky in a motion known as precession.

Over thousands of years, as the axis moves through precession, the stars that are visible at important points in the sky gradually appear to shift. To Gurshtein, this shifting of the visible sky explains the zodiac: New constellations had to be created as others were outdated, with some stars appearing at those points and others disappearing, until the entire belt of 12 was filled in.

But his theories will probably remain just theories, simply because there isn't any evidence to show what people were thinking when they first created star patterns, and reaching back that far into prehistory can only be speculation, other astronomers say. The constellations themselves provide one kind of evidence, though. Astronomers can figure out where and when some of the earliest detailed studies of the stars were made by looking at the oldest star maps available.

Doing this, they see constellations all over the sky except for a roughly circular area around the south celestial pole. That blank area, called the "zone of avoidance," corresponds with stars that couldn't have been seen by people 4,000 years ago living at about 36 degrees north latitude. Because of the way the stars move across the sky, people are limited to seeing only certain stars. Texas viewers, for example, can see part of the Southern Cross only if they are in Corpus Christi or farther south.

The zone of avoidance is centered on the spot that, because of precession, was the south celestial pole around 4,000 years ago. Thus, based on the lack of constellations in this area, astronomers think that the stars were studied in detail around 2000 B.C. by people living at 36 degrees north latitude - along a line that runs in part through the early civilizations of the Mediterranean and the Near East. Other independent evidence also supports this idea. Ancient Greek literature, for instance, describes the stars in detail as they would have appeared not to the Greeks, but to much earlier civilizations.

The earliest known complete reference to constellations is a poem written by the Greek poet Aratus, in about 275 B.C., called The Phaenomena. This poem describes 46 constellations, almost all of which correspond almost exactly to a star catalog published later by Alexandrian astronomer Ptolemy, in the year A.D. 137. But neither Aratus nor Ptolemy created these ancient constellations. The Phaenomena described constellations of the famed "sphere of Eudoxus," an engraved celestial globe studied by the mathematician Eudoxus 100 years before Aratus.

This long-lost globe didn't belong to Eudoxus, either. He, too, was studying something even older than he was. The patterns engraved on the sphere of Eudoxus represented the sky as it appeared around 2000 B.C., says Archie Roy, professor emeritus of astronomy at the University of Glasgow in Scotland. "He didn't understand that the sky he was describing from the globe wasn't anything like the real sky" in his era, says Dr. Roy. "So the question is, where did the globe come from, and why was it past its 'sell-by' date?"

Roy has tried to answer this question by taking clues from Aratus' poem and plugging them into a planetarium program that draws the sky as it appeared at any time, from any latitude. He found that the sky described by Aratus, via Eudoxus, would have been visible between about 2200 B.C. and 1800 B.C. from a latitude of around 36 degrees north - corresponding with the evidence from the zone of avoidance of the constellations.

There are several possibilities for the identity of the people who passed the constellation patterns on to Eudoxus and thus to Aratus. Roy believes that they were from the civilization of Minos, on the Greek island of Crete. Gurshtein's work suggests that the constellations were much older than even the Minoans. He believes that the Minoans may have refined and elaborated on the constellation system, but that the main star patterns were in place possibly even 20,000 years ago.

Gurshtein also believes that the oldest constellations fall easily into three categories, representing water, earth and air, and that they would have been centered on the point that was the north celestial pole around 16,000 years ago. Later, Gurshtein says, other constellations were added and made more important in this ancient system. For example, he thinks the zodiac was introduced over a period of several thousand years.

Here's how he believes it works: About 5600 B.C., four new constellations were discerned to mark the places where the sun lay at the equinoxes and solstices. For ancient civilizations, those four constellations represented important points along the sun's path, as the cardinal directions - north, south, east and west - do on the horizon today.

But a problem arose because of Earth's wobbling on its axis. "Because of precession, the whole thing gradually went out of date," says Roy, who edits Vistas in Astronomy. "And after about 2,000 years somebody had to map out  four new constellations, each a bit ahead of the previous one."

So those initial four constellations were eventually joined by four new ones that marked the new solstice and equinox points. Finally, after another 2,000 years (around 1400 B.C.), the last four zodiacal constellations were mapped out, completing the zodiac. Although astronomers say nobody will ever be able to prove this theory, they call it intriguing.

"I think it's a brilliant idea," says Roy.