mirrored file at http://SaturnianCosmology.Org/ For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== [1]Home [2]People [3]Calendar [4]Undergrad [5]Grad [6]Research [7]Observatories [8]VAIL [9]VITA [10]Public Outreach [11]AQuA [12]Local [13]UVa China The times of particular interest for this course are the Shang Dynasty (about 1600-1100 BC) and the Han Dynasty (about 200 BC - 200 AD). The Han dynasty was preceded by the reign of Emperor Qin, who unified a large part of China. China then covered a large area, including about 20 degrees in latitude. Records were brought to the capital from throughout China, so that differences in astronomical observations at different places could play a role. The Shang Dynasty had been largely in the realm of myth, but around the turn of the century (1900), `oracle bones' with a written record were found in the fields of Chinese farmers. These bones were primarily the scapulae of oxen and turtle shells. The bones were insribed with a primitive version of the Chinese writing. Several permanent stars have been identified from these records and there are possible sightings of `new' stars. Lunar eclipses were noted. The reason for recording the astronomical events is that they were regarded as omens. Prognostications were made for the empire. The standard method of divination is that cracks were introduced into the bones or turtle shells by heating them, and the cracks were then subjected to interpretation. The practice in China of using unusual astronomical events for divination continued for thousands of years. During the Shang Dynasty, the Chinese had in place interlocking cycles of 10 days and 12 days; together, these made a cycle of 60 days. This 60 day cycle was kept, apparently continuously, for thousands of years. Astronomical events recorded by the Shang Dynasty people were noted by the place in the 60 cycle, as well as the lunar month and reign year. With this information on several lunar eclipses, there have been attempts to correlate the Shang calendar with our Christian calendar, but these attempts have not been successful. Before the Han Dynasty, the Chinese developed a method of mapping out the celestial sphere using equatorial coordinates. This was the system of lunar mansions, or xiu. There were 28 lunar mansions, presumably in reference to the sidereal month. These were sections of the celestial sphere, from pole to pole, with varying width. Angles were measured in terms of du, which was slightly less than 1 degree. There were 365 1/4 du in 360 degrees, demonstrating a good knowledge of the solar year. Positions were given as the number of du from the celestial pole and from the edge of the lunar mansion in which the event occurred. Star maps were produced from an early time in China. They tended to place stars in smaller groups than our constellations; these groups are called asterisms. The Chinese had a bureaucratic governing structure. The emperor employed and astronomical directorate that had several divisions. One division was for the imperial astronomer, who was in charge of observations. The sky was closely followed because of the belief that there were omens of importance to the state. The aim was to have 2 observers at a place, both taking notes independently. The notes were then compared, so the reality of celestial events could be checked. However, the observers were sometimes lazy, and one would copy the notes of the other; they could get into serious trouble for this. Another division was that of the imperial `astrologer,' who was in charge of the interpretation of celestial events. Another division was in charge of keeping time by water clocks. There were developments in the design of water clocks in China. Notes were thus compiled during a particular dynasty. When that dynasty was over, the next dynasty would put together a history of the previous one, including astronomical observations and their interpretation. The standard practice was to show how a prognostication was borne out by subsequent events. During the Han dynasty, there were the beginnings of cosmological speculation; debates took place between 3 competing schools of thought. They are of interest because each one had a relation to a particular kind of astronomical observation. The hun tian school emphasized the motion of celestial objects in circles across the sky. They realized the apparent rotation of objects about the celestial pole and developed instruments that took advantage of this fact for determining celestial positions. The basic structure of an armillary sphere is an axis pointed toward the celestial pole, a movable ring that turns on this axis and another, perpendicular, ring. The instrument can be used to obtain positions in celestial coordinates. The kai tian school discussed the structure of the earth and heavens. Using the knowledge that the altitude of the sun changed with position along a N/S line in China, they determined the distance to the sun in a flat earth cosmology. This distance was, of course, way too small. We now know that the sun is very distant, and the change of its altitude with latitude is due to the spherical shape of the earth. The xuanye school is sometimes called the school of infinite emptiness. The notion was that the celestial objects we see are bodies moving in empty space. This correct view is not obvious; many cultures viewed the heavens as a dome over the earth. The bodies were regarded as condensed vapors. This view was supported by the observation of changing spots on the sun. The Han Dynasty observations of sunspots are the earliest known observations of sunspots. The spots can be observed when the sun is behind thin clouds, or through a jade disk. At some point after the introduction of the 60 day cycle, the Chinese starting using a 60 year cycle, made up of 10 year and 12 year components. Twelve years is also a good estimate of Jupiter's sidereal period, so its motion relative to the background stars was carefully followed. At the present time, the use of the 10 year cycle has dropped away, leaving only the 12 year cycle. There are animals associated with each year of the cycle and the Chinese years are labeled with Year of the Rat, etc. Chinese observations of supernovae before 1500 are unparallelled elsewhere in the world. The fact that they were regarded as omens resulted in a lot of attention being lavished on new stars, or "guest stars." Naked eye supernovae are infrequent. The last one to be observed was supernova SN 1987A in the Large Magellanic Cloud, observable only in the southern hemisphere. The previous one was in 1604, observed by Kepler, and the one before that was in 1572, observed by Tycho. Chinese observations were crucial for all the previous supernova observations, in 185, 386, 393, 1006, 1054, and 1181. The Chinese positional observations has allowed a number of these events to be identified with supernova remnants. Of special interest is SN 1054, which has been identified with the Crab Nebula. In 1968, the Crab Nebula was found to contain a pulsar, a very rapidly rotating neutron star. The pulsar gradually spins down, releasing power for the light that we see from the nebula. The data determined from the Chinese observations show that the pieces of exploded star have accelerated since the time of the explosion. Power from the pulsar is the likely source of the power. The Chinese had various ways of measuring lengths. A long length was the li, about half a kilometer, which was used to measure distances like that to the sun. Another common length was the chi, about a foot. A standard gnomon (rod) used to measure solar shadows was 8 chi long. The Chinese did not have a fully functional system of fractions, so that when they needed to go to smaller lengths, they defined a new unit that was 10 times smaller than the previous one. Gnomons were used to accurately measure the maximum altitude of the sun, including the extremes on the summer and winter solstices. The angle between the sun and the equator on those dates gives the obliquity of the earth. Using Chinese observations going back to Han times, Laplace showed in the 1700's that the earth's obliquity is slowly changing. It is currently becoming smaller. There has not been much in the way of detailed studies of astronomical alignments in Chinese buildings. One case is the N/S alignment in the imperial city in Beijing. The temple of heaven is directly to the south of the Forbidden City, where the emperor lived. At the time of the winter solstice, the emperor would move with a procession to the temple of heaven in order to carry out rituals. The aim was to be sure that the sun reversed its course and began to move northward in the sky. _________________________________________________________________ Last modified December 6, 2002 at 16:07:12 EST by [14]rac5x [15]http://www.astro.virginia.edu/class/chevalier/astr341 References 1. http://www.astro.virginia.edu/ 2. http://www.astro.virginia.edu/people 3. http://www.astro.virginia.edu/events/calendar.php 4. http://www.astro.virginia.edu/class 5. http://www.astro.virginia.edu/grad 6. http://www.astro.virginia.edu/research 7. http://www.astro.virginia.edu/research/observatories 8. http://www.astro.virginia.edu/research/instrumentation/ 9. http://www.astro.virginia.edu/VITA 10. http://www.astro.virginia.edu/public_outreach/ 11. http://www.astro.virginia.edu/AQuA 12. http://www.astro.virginia.edu/local 13. http://www.virginia.edu/ 14. mailto:rac5x at virginia.edu 15. http://www.astro.virginia.edu/class/chevalier/astr341