The night sky has been enhanced in recent weeks by an eerie, glowing visitor with glistening streamers, visible in the northwest after twilight and in the northeast before dawn
The object is Comet Hale-Bopp, one of the brightest comets to come along in generations. Discovered independently–and accidentally–in the Southwestern desert by Alan Hale and Tom Bopp, the comet is, for some, a spectacular, once-in-a-lifetime celestial light show.
For others, however, its pale, ghostly presence awakens a primordial fear that disaster is imminent. And for others still, Hale-Bopp offers the unique opportunity to study the very material that more than 4 billion years ago formed our solar system.
It is perhaps difficult to appreciate what the night sky meant to virtually every civilization that preceded us. Our ancestors, not having the advantage of electric lights, were able to experience a truly dark sky filled with seemingly countless points of light.
Ancient civilizations divided such points of light into those that remained in fixed positions as they rose and set each evening–the stars–and those “wandering” objects that became known as planets.
Night after night, season after season, year after year, there was a comforting predictability to the clockwork motions of the sun, the moon, the stars and the planets.
On those occasions when a strange, celestial glow emerged seemingly from out of nowhere to become a bright light with a long, spectral tail, anxiety ran rampant.
The sudden appearance of such an object was viewed as an indicator that, because something was awry in the usual order of the universe, something must also be awry in the natural order of occurrences on the Earth, that disaster–which means, literally, “bad star”–must be at hand.
Of all of the civilizations to keep records of comet appearances, those kept in China span the greatest stretch of time. From 2000 B.C. until the breakdown of the Imperial System in 1911, professional astronomers were hired by the emperor to keep track of celestial events such as the appearance of comets.
“Most of the Chinese records were on old bones, so not all of them have survived,” says Brian Marsden, the director of the International Astronomical Union’s Central Bureau for Astronomical Telegrams in Cambridge, Mass.
“The nice thing is that each oracle bone was devoted exclusively to a comet, as opposed to Babylonian clay tablets, which may talk about comets, but you also get the price of wheat, how the king was feeling, and so on.”
As for the precision of the observations, Marsden points out the emperor had a unique work-incentive program. “Chinese astronomers who failed to predict an eclipse . . . had their heads chopped off as a result,” he says.
In Shakespeare’s “Julius Caesar,” Caesar’s wife notices a comet in the predawn sky of the Ides of March and offers him the pre-assassination warning that “When beggars die, there are no comets seen. The heavens themselves blaze forth the death of princes.”
Religious significance
Likewise, comets were also used as literary devices in subsequent retellings of the birth stories of great religious and military leaders, including Moses, Buddha and Alexander the Great, to say nothing of the familiar Christmas story from the Gospel of Matthew about exotic Magi following a moving star to the Christ child.
“Comets are often a classic apocalyptic symbol in the Judeo-Christian tradition, which is odd in a way because both traditions have traditionally rejected astrology,” says Albert Wolters, professor of biblical studies at Redeemer College in Ancaster, Ontario, Canada.
It was Wolters who determined that the appearance of Halley’s Comet in 164 B.C. coincided with the rededication of the Temple of Jerusalem.
“That is the occasion that is still celebrated by Jews every year at Hanukkah,” says Wolters, adding that even the holiday’s popular nickname of “Festival of Lights” is a tribute to Halley’s illuminating appearance immediately before and after the rededication.
In 1456, a comet so terrorized western Europe that a papal edict was issued requiring the faithful to pray for deliverance from “the Devil, the Turk and the Comet.”
One of the first attempts to explain comets as natural, scientific phenomena came from Greek philosopher Aristotle, who surmised they were exhalations of gases from the ground into the atmosphere. Thus, he saw comets as meteorological rather than celestial in nature, a view that would be widely held until 1577 when Danish astronomer Tycho Brahe compared the measurements of a comet from two separated points on the Earth.
By comparing the comet’s position against the corresponding background stars, a measurement, or a parallax, of the comet’s distance could be determined. Using this method, Tycho calculated the comet of 1577 was at least four times farther away from the Earth than the moon was, which established that comets were objects well beyond the confines of the Earth’s atmosphere.
No connections were seen between the apparitions of comets until Sir Edmund Halley applied the principles of Newtonian physics. Calculating that, like the planets, comets actually traveled in an orbit around the sun, Halley noticed that comets seen in 1531, 1607 and 1682 had very similar orbits, each nearly 76 years apart.
Thus his supposition that the three comets were actually three returns of the same comet, which had an orbit of 76 years. By that calculation, he surmised the same comet should return in 1758, which it did.
Finally, for the first time, the return of a comet could be predicted in advance.
Surprise discovery
In the 20th Century, as in antiquity, comets are viewed with mystery and romance. The skies are scanned by professional and amateur astronomers alike, each hoping to make the discovery of a new one. This was the case in summer 1995, when two stargazers, independent of each other, tracked a “fuzzy object” in the night sky.
The desert of the American Southwest is a nearly ideal location: clear, dark skies during most of the year, with July and August bringing what is called the monsoon season to the area.
Astronomer Alan Hale had moved to Cloudcraft, N.M., precisely because of its magnificent skies. And because a cloudless night in July or August is such a rarity, when the sky cleared on July 22, 1995, Hale decided to take immediate advantage of it.
“There were two comets that I wanted to observe,” says Hale, who had tried to discover comets for many years, but had given up in favor of confirming the discoveries and observations of others.
Being summer, the center of our own Milky Way galaxy was magnificently visible in the constellation of Sagittarius. Hale decided to scope out some of its star clusters.
“One such cluster is called M70, and when I came upon it, I noticed that there was a fuzzy little object near it,” says Hale. “Having looked at M70 two weeks before, there was no such object there at the time, which was odd.”
Of course, the chances of Hale just pointing his telescope in any direction and discovering a comet seemed next to nil, so he checked out a variety of star atlases and catalogs of deep-sky objects to see what might be there.
“There were no known objects there,” says Hale. “Imagine that–after years of actually looking for a comet, I stumbled upon one by accident!”
Meanwhile, a group of amateur astronomers were also marveling at the splendors of M70 out at a “star party” in the Arizona desert.
One member of the group, an amateur astronomer named Thomas Bopp–who had never even seen a comet–was watching M70 go out of view in a friend’s homemade telescope when he, too, noticed a fuzzy object near it. He, like Hale, peered at it for more than an hour to see if the object was moving. It was.
Hence, because of its two independent discoverers, the new comet was dubbed “Comet Hale-Bopp.”
As a preliminary orbit for Comet Hale-Bopp was determined, it became obvious the comet was going to come much closer to the sun, and would even come inside of Earth’s orbit. Hale-Bopp was on its way to becoming one of the potentially brightest comets ever seen.
“There is a record of a comet in Egypt in 2192 (B.C.), but we don’t know that it’s Hale-Bopp, and we don’t that it’s not,” says Brian Marsden. “We do know that the comet has been through here at least once before–about 4,000 years ago–but pinpointing it exactly can be difficult.
“We know, for instance, that Hale-Bopp’s next return has been reduced to about 2,400 years from now, because of a little nudge it received when it was passing near Jupiter this time around. We also know that we haven’t seen a comet this large since 1577, so this is really quite an event.”
A look at our history
David Levy, an amateur astronomer who has discovered 19 comets himself, as well as another dozen with Eugene and Carolyn Shoemaker–including the infamous Comet Shoemaker-Levy 9 that collided with the planet Jupiter in July 1994–agrees Hale-Bopp is unique.
“The beauty of Hale-Bopp is that it is so condensed, which means it can be seen by more people,” says Levy.
In addition to the aesthetic beauty of Hale-Bopp, Levy says that studying such a large comet can help us understand the origins of the solar system.
“We need to study the materials that are in such a large comet,” he says, “the carbon, oxygen, hydrogen and nitrogen, because those materials were detected in Halley’s Comet and we’re trying to detect them in other comets as well. These materials are the building blocks of life, and there’s a theory that the Earth received these building blocks–including its water supply–through comet impacts when it was very young.”
Indeed, Levy reminds us to look at the moon if we want to be reminded of what a dangerous neighborhood we reside in within our little corner of the universe.
“Each of those craters on the moon is the remains of a comet,” says Levy. “The moon’s history is written on its surface, and it’s a violent history–a bombardment of comets, which means the Earth has had that same history, but most of Earth’s craters have been eroded away.”
Hale says the notion of a comet hitting the Earth again is not so much a question of “if” as “when.”
“Sixty-five million years ago, the dust from a collision froze plant and animal life, including our friends the dinosaurs,” says Hale. “Oddly enough, we should be grateful, for if that object hadn’t hit, smaller mammal life forms such as ourselves wouldn’t be here.”
