Nicolaus Copernicus was a Polish mathematician and astronomer who developed the heliocentric theory, which states that the Earth and other planets revolve around the Sun.

The geocentric theory, which was widely accepted before Copernicus, stated that the Earth was the center of the universe and that the Sun and other planets revolved around it.

Copernicus observed that the planets sometimes appeared to move backwards in their orbits, which could not be explained by the geocentric theory. This led him to propose that the planets were actually revolving around the Sun.

Copernicus published his heliocentric theory in his book \"On the Revolutions of the Heavenly Spheres\" in 1543.

The heliocentric theory challenged the religious beliefs of the time because it contradicted the idea that the Earth was the center of the universe, suggested that the Earth was not unique, and implied that humans were not the center of God's creation.

Giordano Bruno was the first astronomer to publicly support Copernicus's heliocentric theory. He was burned at the stake in 1600 for his beliefs.

Galileo used a refracting telescope to observe the planets and moons. This type of telescope uses lenses to focus light.

Galileo's observations of the moons of Jupiter revealed that they revolved around Jupiter, that they were not perfect spheres, and that they had mountains and valleys.

Galileo published his observations of the planets and moons in his book \"Sidereus Nuncius\" in 1610.

The Catholic Church condemned Galileo's observations and theories as heretical because they contradicted the geocentric theory, which was supported by the Bible.

Galileo was forced to recant his heliocentric theory at the Galileo Trial in 1633.

The heliocentric theory was finally accepted by the scientific community in the 17th century, thanks to the work of Galileo, Kepler, and Newton.

Kepler's Third Law states that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun.

Gravity is the force that keeps the planets in orbit around the Sun.

The heliocentric theory is an example of a Copernican Revolution, which is a scientific revolution that challenges the prevailing scientific paradigm.