Heliocentric - Sun Centered - Universe

Although many earlier philosophers had theorized that the Earth was not the center of the universe, it wasn't until the publication of Nicolaus Copernicus' "De Revolutionibus Orbium Coelestium" (On the Revolutions of the Celestial Spheres) that the Heliocentric model of the universe took shape.

Around 1514 Copernicus distributed a small hand written book to a few friends. Even though no author is named on the title page, those who received a copy of "the Commentariolus" (the Little Commentary) knew who had written it. As a forerunner to his theory of a universe with the sun at its centre, the Little Commentary contains seven axioms on which Copernicus would base his conclusions.

1. There is no one centre in the universe.

2. The Earth's centre is not the centre of the universe.

3. The centre of the universe is near the sun.

4. The distance from the Earth to the sun is imperceptible compared with the distance to the stars.

5. The rotation of the Earth accounts for the apparent daily rotation of the stars.

6. The apparent annual cycle of movements of the sun is caused by the Earth revolving round it.

7. The apparent retrograde motion of the planets is caused by the motion of the Earth from which one observes.

While not completed, most of the concept of De Revolutionibus was laid out by 1530. In 1533, Johann Albrecht Widmannstetter, a German theologian, was in Rome, delivering a series of lectures outlining Copernicus's theory. In 1536, Archbishop of Capua Nicholas Schönberg wrote to Copernicus entreating him to share his theories with the scientific community. Copernicus still felt it was not a wise political move to publish a work that would cause a strong negative reaction from the church.

In his book, instead of the geocentric system based Ptolemaic model, Copernicus proposed that a rotating Earth revolving with the other planets about a stationary central Sun provided a much simpler explanation for the same observed phenomena of the daily rotation of the heavens, the annual movement of the Sun through the ecliptic, and the periodic retrograde motion of the planets.

De Revolutionibus Orbium Coelestium was first published by a Lutheran printer in Nürnberg, Germany, in 1543. One often repeated Copernican legend claims that he received a printed copy of his treatise on his deathbed. Nicolaus Copernicus died on May 24, 1543. After its publication, Copernicus' work was ridiculed by the church as well as other astronomers. It would be another 60 years before Johannes Kepler and Galileo Galilei proved him (mostly) right.

While it was a major step in the right direction, Copernicus’ theories were still quite cumbersome and imprecise. Today, we know that the Sun is the center of our solar system, not the universe. We are located about 26,000 light-years from the center of the Milky Way Galaxy, which is about 80,000 to 120,000 light-years across. There are many galaxies in the universe.