This is knowing the universe, the history and philosophy of astronomy. I'm Chris Impey, distinguished professor at the University of Arizona in the Department of Astronomy. In this module, we look at revolutions. The revolution in astronomy that transformed our view of the universe and our place in it. We're going to look at non-western traditions first because there are many traditions that were entirely independent of the schema of Greek philosophy and thought that we talked about in the last module. The Western lineage starts with the Babylonians and runs through Greece and Rome, medieval Islam in Europe, and then to the Renaissance astronomers starting with Copernicus. Finally the scientific revolution led by Galileo and Newton. But completely separate from that were traditions elsewhere in the world, which often had innovative ideas and sophisticated thoughts about their places in the universe. The two major traditions we're going to look at are, ancient China and ancient Maya. They're fundamentally different views of the cosmos from each other and from the Western tradition. In ancient China, astronomy was integral part of the state bureaucracy, was essential for the running of civic affairs. There were court astronomers for almost two millennial that searched for unusual celestial occurrences, like comets and novae. The ancient Maya, by contrast, were obsessed with astronomy and time-keeping. In their culture, Venus was pivotal both in the mythology and the religion and also in the practical astronomy. It governed the way they ran their affairs and conducted conflicts with other cultures. There's a pivotal document called the Dresden Codex, which is the book of Mayan astronomy. We'll start with Chinese astronomy and look at the fact that Europe, Central Asia, and India are all linked by Alexander the Great. To some extent they do share a common knowledge and a common astronomical tradition. But China was isolated from the Western world for over 1,000 years. It had intellectual communication with the West very early, but really retained its own character until the 16th century. With Magellan and others, the voyages around the world shrunk the world and lead to a mapping of the Western tradition into other parts of the world within less than a century. Astronomy in China was based on a writing system developed over 300 years ago that remained in continuous use with some evolution ever since. The history of Chinese astronomy is very reliable and more reliable than other cultures because of this continuous written tradition and because of the longevity and continuity of the Chinese Empire. China had many famous inventors and technological innovators, but the concept of natural law did not seem important to China. Chinese philosophy was mostly concerned with running human affairs or deciding how to live a good life. There were many philosophers in what's called the Axial Age. They were contemporaries of each other in different parts of the world. For instance, Socrates, Buddha, Confucius and Lao Tzu, each of whom founded enormously influential schools of thought and religion were contemporaries roughly of each other. The guiding principle of the universe in the Chinese system is the tau. It's composed of warring opposite principles, Yin and Yang. Yin and Yang make use of five material agents: motions in the heaven, biology, medicine, morality, aesthetics and human history. In this cosmology, Yin and Yang have cycles and the universe was continually recreating itself. It was natural for the Chinese to relate the motion of the stars to courses of action, especially government action. Keeping calendar was of great importance. There were court astrologers for nearly 2,000 years and they were in great demand by the Chinese rulers. These large bureaucracies were in place from very early times. There were two distinct kinds of astronomy developed by the Chinese. One based on the method of calendars, in particular lunar calendars and the other looking at celestial patterns for divination or casting fortunes or telling the future. Here we see a lunar calendar, an example of that Chinese tradition. On the right, we see tianwen celestial patterns, in this case, comet sightings over a period of time from hundreds of years ago. Mathematical astronomy was also developed by the Chinese. Liu Hong created a system of mathematical astronomy and could predict the positions of the sun and moon with reasonable accuracy. These rules were similar in spirit to those of Babylon. They were predictive, but they were not explanatory. The Chinese did not seem to see deeper explanations about the phenomena as the Greeks at the same time were. Yu Hsu possibly discovered the precession of the equinoxes, an extremely subtle motion where the Earth's precession axis rotates in a period of more than 20,000 years. Independently of the Greeks, ephemeral phenomenon such as comets and novae were rarely recorded in the West at this time. But in China, there were careful records lasting over 2,000 years. We see evidence in their records for a whole set of supernovae that are of great importance in historical astronomy. They're really the only record astronomers have of these phenomena. There's also an indication controversial that sunspots were recorded in 28 BC, long before the telescope was invented and sunspots were officially discovered by Galileo. We also have a strong tradition of star maps and use of instruments for observation. The Chinese at the same time as Ptolemy had a list of 1,400 stars compared to the 1,000 in the Almagest. They had a pretty good faint star observing technique to catalog and give positions for that many stars. Here's a water clock, which is a recreation of 1,000 year old construction from Su Song. It has an escapement, an armillary sphere for measuring angles on the sky, an endless chain drive, sophisticated oblique gears. Not clear how they machined those. It's a beautiful piece of apparatus from medieval times. Here is an armillary sphere, a modern recreation of an original from 1439. The Chinese observed the Crab Nebula supernova that exploded in 1054 and was a guest star. It was apparently unobserved in medieval Europe. That's the end of this topic.
