Expert: Jayendra Upadhye - 4/22/2004

Question
Why was earth originally not called a planet?

Answer
Hi Corey,
That was because before the time of Copernicus and Kepler,
people did not look upon the universe, and mainly the solar system, as "helio-centric".
They imagined that the earth was at the center of all things.
That the planets and the sun (along with the moon) moved around the earth!
Since the earth was not thought to be moving around "anything", it was not thought of as a planet.
The occasional retrograde motions seen in the movements of other planets began to cause people to doubt all that and eventually kepler with his laws of planetary motion, laid the foundation for a more concrete and solid helio-centric theory of the solar system.
Around the same time or a little later Newton was writing his "Principia Mathematica" and laying the foundations of the math (advanced differentials and integerals calculus), that would help people put it all down on paper, and digest it and test it.
Newton and Kepler were not alone.
Europe was going thru the renaissance.
other geniuses such as Euler, fermat, laplace, lagrange, tycho, halley, Galileo etc also contributed immensely to these developments in math and physics/astronomy/cosmology.
If you can find time..then..
as i normally do, I have looked up a nice site for you to go into the history of all this..plus gain additional insight..
http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Orbits.html .
If you get your hand on it dont let go of Carl Sagan's classic book "Cosmos".
Jayen.