Fathers of Science
In 1514, a Polish priest named Nicholas Copernicus suggested that the earth revolved around the sun. Copernicus feared what he would face mistreatment if he made a statement that went against popular opinion of the day, so he circulated his statement anonymously. A legend about Copernicus says that a book he wrote about the sun-centered universe was placed in his hands a few days after he lost consciousness from a stroke. He awoke to see that his work had been published, then died peacefully. We don't know if that story is true, but it shows how fearful people at that time were of challenging long held beliefs, even if they were wrong.
Galileo proved Copernicus right in 1609 when he observed the heavens with a telescope, which had just been invented. Galileo observed that Jupiter had several moons orbiting around it. This proved that not every heavenly body had to revolve around the earth.
Scientists understood the world was round, but Isaac Newton explained why people did not fall off the earth. Newton realized that everything in the universe was attracted to everything else, and that the greater and closer the object, the greater its gravitational pull. We call this force gravity, a term that comes from a Latin word meaning heaviness. The earth is very large, so people and objects are attracted to it. The earth had just enough attraction to the sun to keep it in orbit.