Chapter 3
The Ancient Roots of Science
Scientific thinking is based on everyday ideas of observations and trial and error experiments. Observations have aided in keeping track of time and seasons, served practical purposes such as with agriculture, and also served ceremonial and religious purposes. It also aided with navigation. The ancient people of central Africa, for example, could predict seasons from the orientation of the crescent moon. Some achievements of ancient civilizations in astronomy are daily time keeping, tracking seasons and establishing a calendar, monitoring lunar cycles, monitoring planets and stars, and predicting eclipses.
Ancient Greek Science
Our mathematical and scientific heritage originated with the civilizations of the Middle East. The Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or the supernatural. Eratosthenes measured the Earth in the year 240 B.C.E. Greeks explained planetary motion with the Earth at the center of the universe. They also believed the heavens must be perfect, meaning objects moved on perfect spheres. The most sophisticated geocentric model was that of Ptolemy(100-170 C.E.) In the Ptolemaic model, planets moved in small circles while moving in a larger circle around the Earth. The Muslim world preserved and enhanced the knowledge they received from the Greeks while Europe was in the Dark Ages. Al-Mamun’s House of Wisdom in Baghdad was a great center of learning around 800 C.E. With the fall of Constantinople, eastern scholars headed west to Europe, carrying knowledge that helped ignite the European Renaissance.
The Copernican Revolution
Copernicus proposed a heliocentric model in the year 1543 C.E. He used a model to determine the layout of the solar system (in AU). Unfortunately it was no more accurate than the Ptolemaic model in predicting planetary positions. Brahe composed the most accurate naked eye measurements ever made of planetary positions(1 arcminute). However he could still not detect the stellar parallax, thus leading him to conclude that the Earth was at the center of the universe, but he did recognize that other planets moved around the sun. Brahe hired Kepler, who used Tycho’s observations to discover the truth about planetary motion. Kepler tried to match Tycho’s observations with circular orbits, however there was an eight minute discrepancy that eventually led him to make a shift to ellipses instead. The first law of Kepler’s planetary motion states that the orbit of each planet around the sun is an ellipse with the sun at one focus. The second law states that As a planet moves around its orbit, it sweeps out equal areas in equal times, moving faster as it is nearer to the sun. The third law states that more distant planets orbit the sun at slower average speeds, obeying the relationship, p^2=a^3(p=orbital period in years, a=average distance from the sun in AU.) Galileo(1564-1642 C.E.) overcame many objections to the Copernican view. The arguments were, that the Earth could not be moving because objects in the air would be left behind, that non circular objects are not perfect as the heavens should be, and that if the Earth were orbiting the sun we would detect a stellar parallax. However, Experiments proved that objects in the air would stay moving with the Earth, observations made through telescopes and by Tycho had already shown many imperfections, and Tycho thought he had measured stellar distances, but the stars were actually much farther than he had thought.
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