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History's eye on space
http://www.ecns.cn/learning-Chinese/2013/10-08/83377.shtml
Oct 8th 2013, 07:55
2013-10-08 16:55 The World of Chinese Web Editor: Yao Lan
A Chinese imperial astronomer made routine observations in the eastern sky early one morning in 1054. His primary job was to revise the calendar based on the movements of the sun, moon, and other planets so as to guide farming across the country. He was looking at a previously charted area when an anomaly caught his eye―a shining celestial object with white and red rays suddenly appeared near a star now known as Zeta Tauri. It was so bright that it could be seen in broad daylight. Continuing to glow for 23 days, the object began to dim, though it remained for two years before eventually disappearing. The imperial astronomer documented this curious celestial object as a "guest star" (客星 kèxīng). Along with 90 other accounts of guest stars in Chinese astronomical records, it did not draw any attention until the early 20th century.
The Crab Nebula―an oval shaped glowing cloud formed by strings of gas and dust in the Taurus constellation―has long been an object of fascination. First spotted by English doctor and astronomer, John Bevis in 1731, the Crab Nebula was named by Lord Rosse in 1844 who thought the nebula had a tentacle-like structure resembling a crab. Later in 1921, having compared two photos of the nebula taken 11 years apart, astronomer John Duncan found that the nebula was expanding. It was not long before astronomer Edwin Hubble pieced together all the evidence; given the expansion rate calculated from Duncan's observation, the nebula must have originated about 900 years ago from a single source. It was most likely created by a stellar explosion, and―by cross referencing time, location, and historical records―he established the catalyst for the Crab Nebula was first discovered by that imperial Chinese astronomer in 1054.
Today, we know the Crab Nebula as the remnant of a supernova―the brutal end of a star in the form of a cataclysmic explosion, all accompanied by a dramatic increase in luminosity, which in the case of our supernova from 1054 (known as SN1054), some 500 million times brighter than the sun. Further studies revealed a fast spinning neutron star in the center of the nebula. This chain of events, first documented by a Chinese astronomer almost a millennium ago is incalculably valuable in understanding the evolution of stars.
Scientists have been able to glean a great deal by poring over the work of ancient Chinese astronomers. In 185, a guest star (later identified as SN185) suddenly appeared and lingered in the sky for eight months.Recorded in the Book of the Later Han Dynasty (《后汉书》Hòuhàn Shū), it is widely regarded as the first supernova documented in history. Combined with later observations and data, the origins of the explosion and expansion were explained by NASA scientists in 2011. Modern scientific understanding and human history are barely a blip in the world of astronomy.
Ancient Chinese historians' records have helped us, time and time again, in our understanding of stars today. The Orion constellation has a star, Betelgeuse, on his right shoulder. It is known as a red giant that could become a supernova at any moment. However, the same star was recorded as yellow some 2,000 years ago in the astronomical section of the Records of the Grand Historian (《史记》Shǐjì). Before dismissing this as a simple error, it should be noted that such a change is entirely possible. Near its end, a star burns up its hydrogen fuel and begins to expand with increased luminosity and a drop in temperature, all causing its color to change from white to yellow and then to red. If the Chinese historian's account is accurate, what we are witnessing is a new phase in a star's evolution.
Of course, it's not just supernovas that can be found in the annals of Chinese history. Chinese astronomers also took notes on comets, meteor showers, sun spots, and other astronomical phenomena, some that could lead to new discoveries. From the 3rd century B.C. to 1910, all 24 visits of Halley's Comet have been recorded in China.
Stargazers in the northern hemisphere may well have enjoyed the magnificent Perseids meteor shower. Active from late July to late August each year, this famous view in the summer sky was first recorded by Chinese astronomers in 36 A.D.. The earliest record stating, "Over a hundred small meteors were seen gliding in all directions." Up until 1906, a total of 32 cases were identified in various history books and local chronicles.
As amazing as these records sound, it is not an entirely rosy picture for today's scientists. In the case of the guest stars, the term actually referred to a wide range of phenomenona, including supernovas, novas, comets, meteors, and, occasionally, the aurora borealis.
Records can be confusing and cause their own set of problems. In the mid 20th century, a few scientists used records of two eclipses (that could only have been observed in Australia) to claim that the Chinese traveled to Australia in the 3rd century B.C.. On correcting the year "17" to "seven", and "October" to "July", they found the new dates were in fact connected to two other eclipses that could only be seen in Shandong Province.
However, there is an even more serious problem with these ancient records; astronomy and politics were tightly connected. People believed astronomical events were the gods' judgments on the emperor's reign. Zhu Jin, the curator of Beijing Planetarium says, "Because of the connection between politics and astronomy, imperial astronomers occasionally may have omitted or fabricated documents. Modern astronomers should take precaution to distinguish this, and repeatedly assess their accuracy in using these records." Imperial astronomers sometimes made subjective decisions or were influenced to produce false records. For instance, solar eclipses were seen as bad omens, and rulers were not pleased if they were reported.
Obviously, this politicization of astronomy puts a bit of a dampener on some of the grander discoveries claimed in Chinese history books; but, with centuries of study, there's a lot ot be learned.
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