Kepler's Second Law ‒ Simulation

At the beginning of the 17th century the German astronomer Johannes Kepler formed three laws that describe the orbit of the planets around the Sun.



Kepler's first law says that "the planets orbit around the Sun in ellipses (elliptical orbit) in which the Sun is located at one of the two focal points."



Kepler's second law describes how the planets move along their orbits. He argues that "the areas swept by the vector of a planet (ie. line connecting the planet's center of mass and the center of mass of the Sun) are equal in size during equal intervals of time."



This law implies that the movement of the planets (and other bodies) orbiting the Sun in an elliptical orbit is not uniform. The planet is moving the fastest when it passes the Sun in the nearest point of its orbit (ie. Perihelion), and it's moving the slowest when it passes the Sun through the farthest point of the orbit (ie. Aphelion). The animation illustrates the principle of the 2. Kepler's law from which it is apparent that the colored areas S1 to S12, circumscribed by the Earth's vector in equal intervals of time (a month each) also have equal sizes of their area.



Kepler's third law says that "the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit (ie. intermediate distance of the planet from the Sun)."