Ⅰ. History of Astronomy


Astronomy is the oldest science of mankind, and our records of the movements of the heavenly bodies date back to prehistoric times. The oldest surviving text record of astronomical phenomena is a fragment of bone from around 30,000 years ago with representations of the phase of the moon, and the oldest artifact related to astronomy is the megalithic structure located in the outskirts of London, England. This stone structure was erected in positions that coincide with the directions in which the sun and the moon rise and set on the horizon. Astronomy developed independently in various regions including the Middle East, China, India and the American continent. In ancient cultures, the celestial bodies and religion were closely correlated. For example, in ancient Babylonia, astronomy developed to serve the purpose of astrology. In this context, the attempt to distinguish astronomy and astrology in ancient cultures is meaningless.

Pythagoras, who set the foundation of geometry and trigonometry, argued that the earth is round and that all of the heavenly bodies follow circular orbits. Plato, meanwhile, argued that since our observations reveal only an incomplete portion of the cosmos, insights into the mystery of the universe ought to be pursued through reason rather than through observation. Such Platonic teachings thereafter remained enrooted as one of the dominant ideas of Western society for nearly two millennia, up to the time of the Renaissance. Aristotle was the first to adopt the law of physics and to posit that the features of the current universe were attributable to the fact that the universe conformed to this law. He also claimed that circular movement was the only natural form of movement, and that the earth was the center of the universe. Aristarchus was the first scholar to argue that the center of the universe was not the earth but instead the sun, preceding Copernicus’ heliocentric theory by 1700 years.

Eratosthenes accurately determined the size of the earth using a very simple geometric method, and around the 2nd century B.C., Ptolemy ?improved upon the epicycle theory honed by Hipparchus, the theory in which planets were assumed to move in a small circle called an epicycle, to identify the retrograde motion which served as the basis for Ptolemy’s own geocentric theory. For a long period thereafter, there were no significant developments in astronomy. Upon the arrival of the 15th century, however, Copernicus espoused his heliocentric theory, and Kepler, based on his analysis of the observational data regarding Mars compiled by Tycho Brahe, established the three laws which are known as Kepler’s laws even to this day. Meanwhile, Galileo used the telescope to observe the moon and the planets, most notably the phases of Venus, which allowed Galileo to verify that Copernicus’ heliocentric theory was correct. Newton established dynamics as an important field of science, and applied this knowledge to understand the movements of the moon and planets and induced the law of gravity.


  1. What were some of the astronomical phenomena that were known to peoples of ancient civilizations severalthousand years ago?
  2. What was the reason that people denied the orbital motion of the earth for a long period until the emergence of Copernicus’ argument in the Middle Ages?
  3. Explain Ptolemy’s geocentric theory.
  4. How does the appearance of planets and stars differ when observed in the sky?
  5. What method did Eratosthenes use to determine the size of the earth?
  6. How were the people in past able to deduce that the earth was round?
  7. Explain the method of determining latitude in the northern hemisphere.
  8. How did people in the past determine the length of one year?
  9. In what position on the earth can we see half of the sky? Also, where is the position from which we can observe the entirety of the sky?
  10. In what location on the earth would the movement of the stars appear to be parallel to the horizon? Also, where would be the location from which the stars appear to rise perpendicularly to the horizon in the east and set perpendicularly to the horizon i the west?
  11. What method did Copernicus use to explain the revolution of the earth?
  12. What are the astronomical phenomena that respectively support the heliocentric theory and the geocentric theory?
  13. What are some of the astronomical phenomena that fail to be explained based on the geocentric theory?
  14. What are some of the major movements of the planets that can be observed in the skies?
  15. If we accept Ptolemy’s geocentric theory to be valid, in what sequence does the phase changes of Mercury and Venus appear when observed from earth?