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Doctoring the stars.

THE DIVINE PHYSICIAN of Greek mythology, Asclepius, has a celestial alter ego in Ophiuchus, the Serpent Bearer, who is making house calls on this month's all-sky maps. The snake he's bearing is Serpens, the Serpent, and it's split into Serpens Caput (the head), on the west, and Serpens Cauda (the tail), to the east. Shedding their skins, snakes renew themselves, and their regenerative power associated them with healing.

The Serpent Bearer's medical training must have included obstetrics, for he is midwifing the birth of new stars in Messier 16, the Eagle Nebula, in the Serpent's Tail. Embedded in a cluster of young stars, dark fingers of interstellar dust and cold gas dominate this glowing cloud, looking like columns of black smoke against an incandescent curtain. When the Hubble Space Telescope observed the nebula in 1995, its detailed image of these stunning, dynamic towers earned the front page of major newspapers throughout the United States. Believed to be sites of star formation, they were called the "Pillars of Creation." Almost organic in appearance, the dramatic, backlit pillars are probably incubating infant stars.

After the birth of astrophysics, in the second half of the 19th century, astronomers knew that stars condensed from interstellar gas and dust and evolved. Until the 16th century, however, everyone regarded stars as eternal and unchanging, as the Greek philosopher Aristotle had asserted.

The constant heavens of Aristotle were compromised in 1572, when Danish astronomer Tycho Brahe observed a bright new star, or nova, in the constellation Cassiopeia. Unable to detect any parallax, or shift in position, over the time Earth's rotation moved the star across the sky, Brahe correctly understood that the new star lay beyond the Moon.

Four hundred years ago this month, Ophiuchus delivered another "new" star, and Johannes Kepler determined that it also belonged to the celestial realm. Although John Brunowski first spotted this nova through a break in the clouds from Prague on October 9, 1604, Kepler's thorough study of the phenomenon associated his name with the object. When Kepler saw the nova, he realized that the planets Mars, Jupiter, and Saturn accompanied it.

A recent conjunction of Jupiter and Saturn had attracted considerable attention, and the subsequent appearance of a new star in their neighborhood seemed significant. Conjunctions of Jupiter and Saturn are conspicuous and occur every 20 years. Furthermore, skywatchers knew that their meetings migrated systematically through the 12 signs of the zodiac in a pattern that confined the conjunctions to a trigon--a set of three signs spaced evenly around the zodiac. About 10 conjunctions take place in the signs of one trigon before the event shifts to another triplet of signs. The sequence progresses through a third and fourth trigon, and after 804 years the sequence begins again.

Each trigon was associated with one of Aristotle's four traditional elements: earth, water, air, and fire. Aries and its trigon partners--Leo and Sagittarius--inaugurated the conjunction cycle in fire. Kepler's Star appeared after 1603's fiery trigon conjunction in Sagittarius.

In Kepler's time, people believed that the world was about 5,600 years old, and that the Jupiter-Saturn conjunction that started each 804-year cycle signaled the arrival of an important person on the world stage. Adam, the first man in the Old Testament, led the parade of conjunctions out of the garden, followed by Enoch, the father of Methuselah. Eight hundred years later, the third trigon cycle put Noah under the weather. Christ was born five trigon rounds --about 4,000 years--after the Creation. Another eight centuries later Charlemagne ruled the new era. Kepler linked the start of the eighth trigon, in 1603, with his royal sponsor, Emperor Rudolph II.

Accompanying a celestial rendezvous already pregnant with meaning, Kepler's Star prompted people to wonder what it meant. It inspired learned, if misinformed, commentary. Dismissing the wild astrological speculation published by others, Kepler imagined that the new star had formed from some fundamental, though unknown, celestial material, a product of the natural inclination of that heavenly substance to develop structure. Kepler also believed, however, that the remarkable object transmitted a divine message.

Associating the appearance of the new star with the three planets was no accident; he thought the Christmas Star, described in the New Testament's Book of Matthew, was the same kind of phenomenon. In an appendix to De Stella Nova (Concerning the New Star) published in 1606, Kepler referenced the error Lawrence Suslyga had detected in the calendrical conventions that established the year of Christ's birth. Correcting the work of Dionysius Exiguus, a Scythian monk in 6th-century Rome, put the Nativity several years earlier, coinciding with the first Jupiter-Saturn conjunction of the sixth 804-year trigon series. With this analysis, Kepler inaugurated a cottage industry that has manufactured astronomical explanations for the Christmas Star throughout the last four centuries.

Neither the new object Tycho saw in 1572 nor the nova Kepler studied in 1604 was a newly formed star, however. Instead they had each witnessed the catastrophic death of a star. Now known as supernovae, these events blast almost all of a fatally evolved star into a chaotic expanding cloud of stellar debris. The sky temporarily hosts a star hundreds of millions of times brighter than it was. Recognition of the true character of supernovae did not occur until 1933, when Walter Baade and Fritz Zwicky, at Mount Wilson, explained how energetic and exotic these star-killing explosions must be. Had Kepler understood what he had actually seen in Ophiuchus, he might have wondered whether the birth of Christ really would be announced by the cataclysmic death of a star.

Arthur C. Clarke, the science-fiction writer responsible for 2001: A Space Odyssey, put the fate of a planet enveloped by the explosion of its sun to work in "The Star," a story first published in Infinity Science Fiction in November 1955. In this tale, an interstellar mission dispatched to explore a supernova remnant recovers the record deliberately left by a civilization that knew it was doomed. The expedition's detailed analysis confirms that the immolation that ripped that distant sun to shreds was the star that guided the Magi to Bethlehem.

Centuries before anyone imagined the role of gravitational collapse and explosive shock waves in the formation of stars from interstellar material, Kepler explained the appearance of a new star as a natural birth among what were believed to be unchanging stars. Ophiuchus, however, was not delivering a newborn but treating a terminal condition.

STARLIGHT, STARBRIGHT Knowing the sky as well as the streets of Copenhagen, Tycho Brahe understood that he had noticed something special on November 11, 1572. Emerging from his laboratory on his uncle's estate in Denmark, he observed a "new and unusual star, surpassing other stars in brilliancy." Confirming through measurement that the star must be farther away than the Moon, Brahe contradicted Aristotle and demonstrated that there is change in the celestial realm. From Splendour of the Heavens, by T. E. R. Phillips and W. H. Steavenson (1923).

STELLAR REMAINS Four hundred years ago, Kepler observed the last supernova seen in our galaxy. Although the star he saw became no brighter than Jupiter, it was conspicuous and out of place. Eventually the star faded, and in its place today's astronomers now detect only wisps of debris. A false-color image obtained by satellite reveals, however, a spherical shell of expanding gas. What Kepler imagined as a star busy being born is, in fact, the scattered remains of a star busy dying.

PLANETARY SIGNIFICANCE Conjunctions of Jupiter and Saturn are known as "great conjunctions." Johannes Kepler detailed the regimen for recurrent conjunctions, which occur every 20 years and successively occupy one of three different signs of the zodiac spaced equally around the path of the Sun. Gradually, the conjunctions migrate out of one triplet (or trigon) and into the triplet comprising the signs just east (counterclockwise) of the signs they've abandoned. Each triplet is affiliated with one of the traditional elements: earth, water, air, and fire. The conjunctions between 1583 and 1763 are included in this diagram from Kepler's De Stella Nova, and the 1603 conjunction is punctuated with a star symbol for the 1604 supernova.

E. C. KRUPP prescribes astronomy at Griffith Observatory in Los Angeles.
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Author:Krupp, E.C.
Publication:Sky & Telescope
Geographic Code:1USA
Date:Oct 1, 2004
Words:1363
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