# Kepler’s Laws, What Are Kepler’s Laws?

June 27, 2021Kepler’s laws of planetary motion are three mathematical laws that describe the motions of planets in the Solar System. They were discovered by the German mathematician and astronomer Johannes Kepler (1572-1630).

By examining the data obtained as a result of the observations made by Tycho Brahe, Kepler found that the records that Brahe kept with the positions of the planets could be explained with three relatively simple mathematical expressions.

1st Law: Every planet moves on an ellipse where the sun is at one of its centers.

Law 2: The line connecting a planet to the sun sweeps out equal areas in equal time intervals.

3rd Law: The square of a planet’s orbital period is directly proportional to the cube of the major axis length of the ellipse it orbits.

Kepler’s laws challenged Aristotelian and Ptolemaic astronomy and physics. He radically changed astronomy and physics, saying that, quite unlike the Ptolemy model, the variable velocities of the planets could be explained with accuracy by claiming that all the planets revolved around the sun in elliptical orbits. Almost a century later, Isaac Newton showed that Kepler’s laws could be revealed by using Euclidean geometry, starting from his own laws of motion and the law of universal gravitation that he also discovered.

Today, Kepler’s laws are used to calculate the approximate orbits of artificial satellites and some objects orbiting the sun (such as distant planets and small asteroids) of which even Kepler was unaware. These laws are very useful in explaining the motions of relatively small objects around larger and more massive objects, when atmospheric friction, relativity, and the influence of other bodies are not taken into account.

Prepared by: Sociologist Ömer YILDIRIM

Source: Omer YILDIRIM’s Personal Lecture Notes. Atatürk University Sociology Department 1st Year “Introduction to Philosophy” and 2nd, 3rd, 4th Grade “History of Philosophy” Lecture Notes (Ömer YILDIRIM); Open Education Philosophy Textbook