Tag Archives: Physics

KEPLER: Epitome of Copernican Astronomy [Book IV, Part II, Ch. 1-2]

Johannes Kepler published Book IV of the Epitome of Copernican Astronomy in 1617. In Book IV, Kepler formally presents his three laws of planetary motion that resolve the problems associated with the epicycles of Copernicus’ heliocentric model. Kepler’s First Law is called the Law of Ellipses. It states that “the orbits of the planets are ellipses, with the Sun at one focus.” Kepler’s Second Law is called the Law of Equal Areas in Equal Time. It states that “the line between a planet and the sun sweeps out equal areas in the plane of the planet’s orbit over equal times.” Kepler’s Third Law is called the Law of Harmony. It states that “the time required for a planet to orbit the sun, called its period, is proportional to half the long axis of the ellipse raised to the 3/2 power.” Although Kepler discovered these Laws, he did not know how they worked. Newton solved this problem with his Theory of Gravity.

COPERNICUS: Revolutions of the Heavenly Spheres [Introduction—Book I-Ch. 11]

Nicolaus Copernicus published the Revolutions of the Heavenly Spheres in 1543. In Book I, Copernicus presents his heliocentric model of the universe. He argues that the Sun, not the Earth, is the center of the universe. He also correctly determined the order of the planets. He wrote that the planets revolve around the Sun in the following spheres – Mercury, Venus, Earth, Mars, Jupiter, and Saturn. However, he stubbornly held onto the belief that the planets must revolve around the sun in perfect circles; for God is perfect. This caused him to mistakenly retain Ptolemy’s system of epicycles to explain the motions of the heavens. Continue reading COPERNICUS: Revolutions of the Heavenly Spheres [Introduction—Book I-Ch. 11]

ARISTOTLE: Physics [Book IV, Ch. 1-5, 10-14]

In this selection from Physics, Aristotle discusses the nature of place and time. He defines place as an immobile container. Everything exists within a place. That which is in no place is nothing. Place, therefore, is the first thing of all creation; for bodies need place to exist, yet place does not require bodies to exist. The presentation of the various arguments against the existence of place and Aristotle’s refutations were tedious. This is the type of caviling that causes many people to conclude that philosophy is a trivial study concerned only with the most irrelevant considerations. Continue reading ARISTOTLE: Physics [Book IV, Ch. 1-5, 10-14]