Shedding light on an ancient supernova.

The twinkling light appeared low on the horizon, outshining everything but the sun and the moon. This "guest star," witnessed by Chinese and Japanese astronomers in A.D. 1054, was a supernova explosion--the violent death of a massive star.

The remnant of that explosion, the Crab nebula, is one of the most photographed objects in the heavens and has endured for nearly a millenium.

So has a mystery about the supernova that forged it.

Asian astronomers carefully documented the supernova, and some Native Americans may have drawn it. However, no evidence clearly revealed that the supernova was seen in Europe. That omission had been attributed to bad weather, but poor viewing conditions in Europe couldn't have lasted the entire 2 years that the supernova was visible, says George W. Collins II of Case Western Reserve University in Cleveland.

"It just stuck in my craw to have to try to weasel out of a perfectly reasonable question with an unreasonable answer," he says. So he set out to investigate.

Reexamining chronicles and religious documents that touch on events from 1054 but were written several hundred years later, Collins' team has gathered a string of clues that European skywatchers did indeed observe the supernova in the evening sky. He and his Case Western collaborators, William P. Claspy and John C. Martin, describe their findings in the July PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC.

Those documents had never been assembled in a single analysis, Collins notes. He adds that some of the material had been misconstrued. For example, a new interpretation of the Rampona Chronicles, an Italian treatise on the universe, indicates the evening appearance of a bright star.

In searching for consistency among the various texts, Collins' team finds that the supernova may have exploded a few months earlier than July 4, 1054, when Asian astronomers first reported it.

Pushing the supernova's debut back several months jibes with the suggestion of other researchers that "an orb of extraordinary brilliance," as was reported shortly after the death of Pope Leo IX on April 19, 1054, was in fact the supernova. The pope was promptly made a saint.

Collins' team "is the first to put together all these disparate (and weak) claims to make a plausible whole," says Bradley E. Schaefer of Yale University. He gives the earlier supernova date "a 50-50 chance" of being correct.

One puzzle remains, notes Collins. No surviving document indicates that Europeans ever saw the supernova in the morning, as the Asians did. His team speculates that the Roman church may have suppressed such recordings, fearing that an opposing faction would herald the morning apparition as a bad omen for changes the clergy was enforcing. "This is at least as good a hypothesis as bad weather," quips Collins.