Johannes Kepler, like Copernicus, put forth a model of the universe (solar system) where the Sun, not the Earth, served as the center. However, contrary to the Copernican model, Kepler’s postulated that these orbits were elliptical, with the Sun located at one of the ellipse’s foci. Along with two other observations, that the radius of an orbit sweeps out equal areas in equal times and that the square of a planet’s orbital period is proportional to the cube of its semi-major axis, Kepler formulated his now-famous laws of planetary motion (Breinig, n.d.). Isaac Newton later studied and improved upon Kepler’s work. For example, using Kepler’s first and second laws, Newton formulated his law of universal gravitation (F = G (m1m2)/r2).
2 major events in astronomical history took place during Kepler’s lifetime. The first occurred on October 17, 1604. This was when Kepler observed a supernova (SN 1604). This event, along with Tycho Brahe’s observations of the supernova of 1572, provided evidence that refuted the then-accepted Aristotelian view of the immutability of the heavens (Vishwanath, 2004).
In 1610, Galileo Galilei published the Sidereus Nuncius, which recorded the astounding observations of the heavens he had made with his telescope (i.e. Jupiter and its moons), and sent a manuscript to Kepler (Van Helden, 1989). While Kepler responded to Galileo with support, the views Galileo put forth went against the doctrine of the Catholic Church, foreshadowing Galileo’s future troubles.
An influential historical figure in Kepler’s time was the aforementioned Tycho Brahe. Kepler served as an assistant to the Danish astronomer. Brahe is remembered for his incredibly detailed observations of the night sky and planetary motion, unparalleled at the time, and it is Brahe’s work that Kepler would turn to when formulating his three laws.
While this overview is brief, what strikes me is Kepler’s lasting influence on Isaac Newton, a man regarded as one of the most influential scientists to ever live. Part of Newton’s magum opus, the Philosophiae Naturalis Principia Mathematica, incorporated Kepler’s work. Kepler’s laws, and Newton’s work on them, are fundamental to the field of astrophysics. Even a brief overview makes one thing very clear: Kepler’s role in the advancement of astronomy, and classical physics, cannot be understated.
Galilei, Galileo. (1989). Siderue nuncius or the sidereal messenger. (A. Van Helden, Trans.). Chicago, IL: University of Chicago Press. (Original work published 1610).
Vishwanath, P.R. (2004). Four hundredth anniversary of Kepler’s supernova. Current Science, 87 (7), 1013-1015.