Who Was He?
On December 27, 1571, Johannes Kepler was born. He studied at a Protestant institution about theology, philosophy, astronomy and mathematics. He often looked up to famous scientists for their work. Which inspired him to learn more about astronomy.
Why Is He A Hero?
He had 3 theories about astronomy. One theory was that the orbit of every planet is an ellipse with the sun at one of the two focuses. This means that the distance between the Sun and the planet varies as the planet goes around. Instead of two parallel orbits, they orbit in different lengths. His second law states; "A line joining a planet and the Sun sweeps out equal areas in equal intervals of time." Basically, a planet orbits faster when it's closer to the Sun and slower when further away from it. The third laws says; "The square of the orbital period of a planet is directly proportional to the cube of the semi- major axis of its orbit." This means that, if the planet is further away from the Sun, the longer it's orbit takes, so he's pointing out that they each have different orbit periods.
The Sun is at one of the focuses while the planet orbits.
Planets travel slower when further away from the Sun.
Each planet is different distances from each other making each ones orbital period take longer.