Op-ed article in the NY Times today -
By FRANK WINKLER
Published: May 5, 2006
Forum: Space and the Cosmos
HOW often do we get to celebrate the thousandth anniversary of anything? Younger readers may live to mark the millennium of the Battle of Hastings on Oct. 14, 2066, but surely none of us will be around on June 15, 2215, to celebrate the 1,000th anniversary of King John placing his seal on the document that became the Magna Carta.
This week, however, marks the millennium of a significant event for astronomers. On May 1, 1006, a new star suddenly appeared in the southern constellation Lupus, the wolf. Within a few days it brightened and became what was probably the brightest star ever witnessed in recorded human history — an event that astronomers today recognize as a supernova, the cataclysmic explosion that marks the death of a massive star.
The true cause of such celestial events was not clear in 1006, and their interpretation was the province of court astronomers, who served as astrologers as well. One of these was Zhou Keming, who wisely declared that the star's brilliance and golden color were portents of good fortune for the land where it appears — and received a promotion from the Chinese emperor.
Observers throughout the world recorded this dramatic event. In the Middle East and Africa, astronomers in Antioch, Alexandria, Cairo and Baghdad compared it with Venus, and even with the Moon, in brightness.
At the Abbey of St. Gall in Switzerland, where the star could barely be seen over the southern Alpine horizon, chroniclers nevertheless described it as the most significant event of the year: "a star of unusual magnitude, shimmering brightly...in the extreme south, beyond all the constellations." And the Japanese poet Fujiwara Teika two centuries later celebrated the fame of the "great guest star" in his "Diary of the Clear Moon."
Aided by historical records, modern astronomers have identified what remains of the 1006 supernova today — a faint shell of gas about 7,000 light-years away. While we cannot be certain just how bright it appeared 1,000 years ago, opinion is virtually unanimous that no other star in recorded history was as bright.
Readers with reasonably dark skies can get an idea of how bright the star would have appeared in 1006 by a simple comparison. The brightest object (after the Moon) in the current evening sky is the planet Jupiter, low in the southeast. Just below it, by about the width of a finger held at arm's length, is a relatively faint star. At its brightest, the 1006 supernova would have been as much brighter than Jupiter as Jupiter is compared with that faint star.
It would have been bright enough to read by (for those few who could read in the 11th century) and could be seen even in daytime for weeks. Like all supernovae, it gradually faded, but remained visible for at least two and a half years, according to Chinese records.
Certainly these are rare events; the most recent in our own Milky Way galaxy to have been unquestionably visible to the naked eye was in 1604, just five years before Galileo first trained his telescope on the heavens. The only supernova since 1604 bright enough to be seen without a telescope was one visible to observers in the Southern Hemisphere in February 1987. It occurred not in the Milky Way, however, but about 170,000 light-years away in the Large Magellanic Cloud, our nearest neighbor galaxy.
Humans have particular reason to celebrate this anniversary. Within a supernova's fires of destruction are forged chemical elements that may eventually be incorporated into new stars, and planets and their inhabitants. Us, for instance. Most of the atoms in our bodies — the oxygen we breathe, the calcium in our bones, the iron in our hemoglobin — all stem from supernovae that occurred billions of years ago. And so, on the 1,000th anniversary of this stellar event, you might take a moment to get in touch with your cosmic roots and reflect that we are, in a very real sense, children of the stars.
Frank Winkler is a professor of physics at Middlebury College.