Johannes Kepler was a brilliant scientist. He was born on December 27, 1571, he was a sickly child and his parents were poor. But his evident intellectual talent got him into a college. Later in his life, he moved to Prague to study under the renowned astronomer, Tycho Brahe. When Brahe died, Kepler inherited his work and his post in the society. Using Tycho Brahe's precise calculations, Kepler continued his work and came up with these 3 laws of Planetary Motion,

that we are still using today.

 

Table of Contents

• Kepler's 1st Law

• Kepler's 2nd Law

• Kepler's 3rd Law​

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

KEPLER'S 1ST LAW

 

The orbit of a planet is an eclipse with the sun at of the focus.

 

Watch this short clip explaining this law.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This law is pretty straightforward, but before Kepler, everyone believed that all orbits were circular. That was because the earth's orbit around the sun is almost perfectly circular, unlike the rest of the planets orbit.

 

KEPLER'S 2ND LAW

 

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

 

This means that if you take a planet at the farthest point in its orbit from the sun a measure the distance it travels in a day, then do the same but when it's at its closest point to the sun, the area that is covered in a day would equal the same.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As you can see in the picture, this means that the planet is moving faster when it is closer to the Sun. This makes sense because as the planet nears the sun, the gravity gets stronger speeding up the orbit.

 

 

KEPLER'S 3RD LAW

 

The orbital period of a planet squared , is proportional to the semi-major axis cubed.

 

The orbital period of a planet is the time it takes a planet to complete 1 round around the sun and it is represented by the symbol , p. The major axis of a planet is a line segment that runs through the center and both foci, with ends at the widest points of the perimeter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

And the semi-major axis is half of this and it represented withe the symbol a.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This video explains this very well.