news center

Double dawn

Double dawn

作者:壤驷惦  时间:2019-03-07 11:08:00  人气:

By Marcus Chown WHEN New Scientist’s readers and reporters recorded their impressions of this year’s eclipse*, they were following a tradition dating back to 899 BC. So say Chinese astronomers who believe they have pushed back the date of the earliest documented solar eclipse by nearly 200 years. Their claim centres on the Bamboo Chronicle, a text transcribed in the 3rd century AD from inscriptions carved into bamboo unearthed from the tomb of King Wei Xiang, who ruled around 500 BC. “During the first year of King Yi,” the chronicle notes, “the day dawned twice at Zheng.” This king is thought to have reigned somewhere between 1100 and 840 BC, and the town then known as Zheng lay near the city of Xi’an. Now a team comprising Ciyuan Liu of the National Astronomical Observatories in Lintong, Jianke Li, currently at the Australian National University in Canberra, and Xiaolu Zhou of Northwest University in Xi’an has calculated that such an event could only have occurred on 21 April 899 BC. “There is only one,” says Li. The Chinese eclipse of 899 BC was “annular”, which means the rim of the Sun remained visible. But the researchers say there would have been a noticeable darkening in the sky. If the eclipse was near dawn, people would have seen the sky mysteriously brighten, darken, then brighten again—a second dawn. Their claim is controversial, however. “In the whole of Chinese history there is no other mention of a double dawn,” says Richard Stephenson of the University of Durham, who has studied the history of Chinese astronomy. He argues that eclipses were well understood by the ancient Chinese. The earliest record of a solar eclipse claimed before now, dating from 708 BC, is also from China—and its chroniclers clearly knew they were watching the Moon passing over the face of the Sun. Li, however, maintains that astronomers were still ignorant of solar eclipses in the Xi’an region in 899 BC. Stephenson also questions the Bamboo Chronicle’s authenticity, as it was copied from inscriptions lost many centuries ago. But if Li’s claim can be proved, it will allow astronomers to calculate the rate at which the Earth’s spin is slowing by comparing the location of the ancient eclipse with the predictions of modern theory (New Scientist, 30 January, p 30). “The further back we can go the more accurate our estimates,