Kepler's Second Law
- A Historical Note

Based on what we know of ancient civilizations, it seems that the study of the motion of celestial objects was considered of great importance. Before the invention of the telescope in the seventeen century, observations were made with the naked eye. Nonetheless, with great patience and ingenuity, astronomers were able to chart the motion of many stars and planets across the sky. Tycho Brahe, a Danish astronomer (1546-1601), was credited to have made very careful observations of the motion of planets in the sky. Originally Tycho thought that planets went around the Sun in circles with the Sun slightly off center. One of his assistants, Johannes Kepler (1571-1630), carefully studied the tables of the positions of Mars in the sky, and came up with three laws.

First Law: Planets move around the Sun in elliptical orbits.

Second Law: The line joining a planet with the Sun sweeps equal areas in equal times.

Thirs Law : The squares of the periods of planet orbiting around the Sun are proportional to the cube of the major semiaxis of their respective elliptic orbits.