Ancient Chinese Astronomers Earn New Respect

This article demonstrates how important - and how seriously - the ancient Chinese took their astronomical observations. According to Joseph Needham, it is quite possible that the precursor of Xiang Qi (Chinese chess) was Xiangi Xi - the "astronomical" game, invented possibly 50-100 years before Xiangi Qi appeared. Ancient Chinese Astronomy: New insights from old information 26 Nov 2007 By Nigel Henbest China has the world’s longest-running observations of the sky: though based in astrology, they are of unique importance to astronomy today. In 210 BC, the great First Emperor of China was buried near Xi’an with his famous Terracotta Army of full-sized clay warriors. According a contemporary account, his own tomb – yet to be excavated – was even more lavish, containing a fabulous double map: “Below was a map of the Earth. The hundred rivers of the Empire were modeled in mercury: cleverly designed machines made the rivers flow. Above everything was the starry vault.” This map reflected the crucial role that the sky played in ancient Chinese thought. The heavens weren’t remote from everyday life. The sky was a mirror of the Earth. Every time that something unexpected occurred in the sky, it showed a disruption on the Earth – which, in effect, meant somewhere in China. To pinpoint exactly where, the Chinese split the stars into 283 small constellations, representing different parts of the Empire. On 7 December, AD 185, for instance, Chinese astronomers spotted a brilliant new star and reported: “A guest star appeared within the Southern Gate. It was as large as half a mat; it showed the five colours and it scintillated.” The Astronomer Royal alerted the Emperor, and decisive action was taken against the region corresponding to the Southern Gate. “The governor of the metropolitan region Yuan Shao punished and eliminated the middle officials… and several thousand people were killed.” The Chinese astronomers kept watch from a raised platform, where four observers faced north, south, east and west; while a fifth lay on his back and looked straight upwards – surely the best job! The next morning they reported to the Astronomical Bureau, which kept records from 206 BC to AD 1912 – the longest-lived bureaucracy the world has ever seen. Today, astronomers can mine this ancient archive for unique information on astronomical events. New insights from old information British astronomer Richard Stephenson, who taught himself ancient Chinese and is now a leading expert on the astronomy of the Far East, has looked into the “guest star” of AD 185. He identifies the Southern Gate as the two bright stars Alpha Centauri and Beta Centauri. And he concludes that the guest star was so brilliant that it had to be a nearby supernova – the most violent kind of stellar explosion. Led by the Chinese results, Stephenson has pinpointed where the explosion occurred. And here astronomers studying X-rays from the Cosmos with the orbiting Chandra Observatory have located the incandescent fireball still expanding from the 2000-year-old explosion. “One of the key things is that you have a definite date,” Stephenson explains, “so you know precisely how long the remnant has been evolving.” The Chinese observations can also indicate how bright the supernova was. “In the case of a supernova seen in AD 1006,” Stephenson continues, “the Chinese said it was so bright that you could see things on the ground by its light.” These ancient observations really come into their own with the supernova spotted in July AD 1054. A star exploded in the constellation we know as Taurus, shining so brilliantly it was visible in daylight for 23 days. Today, in this location we find the twisted wreck of the long-dead star: the Crab Nebula. It’s powered by a collapsed core of the old star, which lurks at the centre of the nebula as a pulsar – a super-dense ball of neutrons only 25 km across, spinning around 30 times a second. Astronomers and physicists are short in understanding how neutron stars change as they grow older. With the Crab Pulsar, the Chinese observations provide a unique piece of information: the pulsar’s age. We know that it was born exactly 953 years ago. The Chandra Observatory has also pinpointed pulsars within supernova remnants that - according to Stephenson - are the fireballs from stars the Chinese saw explode in AD 386 and 1181. Sometimes, the imperial astronomers were treated not to a guest star, but to a “broom star” – a fuzzy object that crawled across the sky, sweeping the sky with its tail. In 240 BC, they set down the world’s first record of the celestial visitor we now know as Halley’s Comet. In AD 530, the Chinese recorded Halley’s Comet with more precision: “On 1 September, it was one degree to the northwest of Xiatai [a star in Ursa Major].” These early fixes on the comet’s orbit meant that European mission controllers could predict its 1986 apparition with greater accuracy, enabling them to send the Giotto spacecraft through the comet’s heart with unerring precision. Ancient Chinese Eclipse Predictions The Chinese were also careful to record eclipses of the Sun – a portent of doom that would directly affect the Emperor or his family. “There was a total eclipse in 181 BC,” says Stephenson, “and the Emperor’s dowager was really alarmed by it: she died two years later.” An eclipse features in the earliest astronomical record in the world, from the Chinese city of Anyang. Around 3000 years ago, a diviner inscribed a question on an oracle bone – a polished shard of animal bone: “Diviner Ge asks if the following day will be sunny or not.” He pushed in a red-hot needle, and interpreted the ensuing cracks. Twenty-four hours later, the diviner inscribed the actual answer to the question. In this case, something rudely interrupted the sunshine: “Three flames ate the Sun, and big stars were seen.” This is clearly an account of a total solar eclipse. The “flames” were the Sun’s outer atmosphere, the corona, with the brighter stars and planets becoming visible during the darkness of totality. To astronomers’ eternal gratitude, Diviner Ge recorded that the eclipse fell on the 52nd day of the 60-day lunar month. In 1989, NASA researchers calculated when a total solar eclipse would have been seen in China on the 52nd day of any month. The only date that fits is 5 June 1302 BC – making this eclipse the most ancient exactly dated astronomical event. This eclipse isn’t important only as a record-breaker. It reveals new information about the Earth’s rotation. Astronomers know that our day is gradually getting longer, due to the influence of the Moon’s gravity – that’s why we have to occasionally insert “leap seconds” to our clocks. But the rate of slowing isn’t constant. By studying exactly where eclipses have been seen over the past millennia, Stephenson has tracked the variation in the Earth’s rotation rate. As well as the Moon’s influence, he has to invoke minute changes in the Earth’s shape as the surface bounces back from the weight of ice sheets that burdened northern lands during the last Ice Age: “especially in the area around the Gulf of Bothnia, the land’s still rising at quite a rate.” These results are showing – in a way the ancient Chinese could never have predicted – that their scrutiny of the heavens has indeed been mirrored in the planet under their feet!