Tycho Brahe

In the late 16th century Tycho Brahe invented the Tychonian or Tychonic system which was a model of the solar system.

Galileo was able to observe Venus going through a full set of phases, something prohibited by the Ptolemaic system (which would never allow Venus to be fully lit from the perspective of the Earth or more than semi-circular). This observation essentially ruled out the Ptolemaic system, and was compatible only with the Copernican system and the Tychonic system and other geoheliocentric models such as the Capellan and Riccioli's extended Capellan model.

The Ptolemaic Model followed a geocentric model of the solar system.

This was then challenged by Nicolaus Copernicus, who claimed a heliocentric model which sparked an integral part of the Scientific Revolution called, the Copernican Revolution.

Copernicus' proposal was followed by the Tychonic Model, with attempted to compromise with the geo- and heliocentric models.

Then, Kepler improved by suggesting elliptical orbits.

The Copernican Revolution came to a close with further speculation from Galileo Galilei and Isaac Newton

TL;DR Because they were wrong

The twelve system of the human body are Skeletal System, Muscular System, Circulatory System, Exretory System, Nervous System, Digestive System, Resperatory System, Reproductive System, Immune System, Lymphatic System, Integumentary System and the Endocrine System.