Geocentric Model - Gravitation

Gravitation

Johannes Kepler, after analysing Tycho Brahe's famously accurate observations, constructed his three laws in 1609 and 1619, based on a heliocentric view where the planets move in elliptical paths. Using these laws, he was the first astronomer to successfully predict a transit of Venus (for the year 1631). The transition from circular orbits to elliptical planetary paths dramatically changed the accuracy of celestial observations and predictions. Because the heliocentric model by Copernicus was no more accurate than Ptolemy's system, new mathematical observations were needed to persuade those who still held on to the geocentric model. However, the observations made by Kepler, using Brahe's data, became a problem not easily overturned for geocentrists.

In 1687, Isaac Newton devised his law of universal gravitation, which introduced gravitation as the force that both kept the Earth and planets moving through the heavens and also kept the air from flying away, allowing scientists to quickly construct a plausible heliocentric model for the solar system. In his Principia, Newton explained his system of how gravity, previously considered to be an occult force, conducted the movements of celestial bodies, and kept our solar system in its working order. His descriptions of centripetal force were a breakthrough in scientific thought which used the newly developed differential calculus, and finally replaced the previous schools of scientific thought, i.e. those of Aristotle and Ptolemy. However, the process was gradual.

In 1838, astronomer Friedrich Wilhelm Bessel successfully measured the parallax of the star 61 Cygni, disproving Ptolemy's assertion that parallax motion did not exist. This finally substantiated the suppositions made by Copernicus with accurate, dependable scientific observations, and displayed truly how far away stars were from Earth.

A geocentric frame is useful for many everyday activities and most laboratory experiments, but is a less appropriate choice for solar-system mechanics and space travel. While a heliocentric frame is most useful in those cases, galactic and extra-galactic astronomy is easier if the sun is treated as neither stationary nor the center of the universe, but rotating around the center of our galaxy, and in turn our galaxy is also not at rest in the cosmic background.