100 GSDoAT - Planetary Motion (5)

Planetary Motion

Year of Discovery: 1609
What is it? The planets orbit the sun not in perfect circles, but in ellipses.
Who discovered it? Johannes Kepler


 Even after Copernicus simplified and corrected the structure of the solar system by discovering that the sun, not the earth, lay at the center of it, he (like all astronomers before him) assumed that the planets orbited the sun in perfect circles. As a result, errors continued to exist in the predicted position of the planets. Kepler discovered the concept of the ellipse and proved that planets actually follow slightly elliptical or bits. With this discovery, science was finally presented with an accurate pictures of the position and mechanics of the solar system. After 400 years of vastly improved technology, our image of how planets move is still the one Kepler created. We haven’t changed or corrected it one bit, and likely never will.

Fun Fact:

Pluto was called the ninth planet for 75 years, since its discovery in 1930. Pluto’s orbit is the least circular (most elliptical) of all planets. At its farthest, it is 7.4 billion km from the sun. At its nearest it is only 4.34 billion km away. When Pluto is at its closest, its or bit actually slips inside that of Neptune. For 20 years out of every 248, Pluto is actually closer to the sun than Neptune is. That occurred from 1979 to 1999. For those 20 years Pluto was actually the eighth planet in our solar system and Neptune was the ninth!