# Renaissance Astronomy

### at the Renaissance Museum of Science and Art

507.349.2874

483 Galileo Rd.

St. Peter, TX 78394

## Nicolaus Copernicus

Copernicus’ theory, *De revolutionibus,* about the universe, provides complex mathematical equations that explain the movement of the planets based on a helio-centric model. However, his theory was obscured by additions to the book. Before final printing, an unsigned preface by a Lutheran pastor named Andreas Osiander was inserted without Copernicus’ permission or knowledge. It preface declared that the Copernicus was only presenting a hypothesis which could improve astronomical computations, rather than asserting that the Earth truly revolved around the Sun. For the first fifty years after its printing, most astronomers focused on using the geometrical models to better predict planetary positions rather than using Copernicus’ heliocentric theory.

## Galileo

While examining Jupiter in January 1610, Galileo noticed that the planet was surrounded by several little stars arranged in a straight line. Successive nights of observation revealed that these “stars” were moons orbiting Jupiter, just as the Moon revolves around the Earth in the Copernican system. Galileo quickly published his discoveries in a small book entitled *Siderius Nuncius*, or *Starry Messenger*. Over the next two years, Galileo would also observe sunspots, the “appendages” of Saturn which astronomer Christiaan Huygens would prove to be the planet’s rings in 1656, and lunar topography. He also observed that the planet Venus went through a complete sequence of phases, just like the Moon.

## Johannes Kepler

Johannes Kepler was able to use Tycho Brahe's observational records, along with the heliocentric theory of Copernicus and English philosopher William Gilbert’s theory of magnets, to create a new model of planetary orbits including the Sun’s influence on them. Kepler found out that the planetary orbits were elliptical rather than circular, and formulated the mathematical rules which give the period and size of a planet’s orbit.

## Issac Newton

Isaac Newton, a mathematics professor at Cambridge University, had tackled the problems of gravitation and planetary orbits on his own throughout the 1660’s and 1670’s. He found the available mathematical tools, arithmetic and geometry, to be inadequate for his use, so he created a new mathematics – calculus – to calculate the effects of gravitation on the motion of celestial bodies. Newton was persuaded to share his mathematical proofs with the Royal Society. His drafts culminated in the publication of the Principia, in 1687. The Principia explains Newton's Calculus and principles of dynamics, discusses his three laws of motion and the law of gravity.Tying together the work of Kepler and Galileo, the Principia proved that the planetary orbits and falling objects on Earth were proved by the same universal force, gravity, and that the effect of gravitational forces on the planets produced their elliptical orbits. Since Copernicus first proposed that the Earth and the other planets revolved around the Sun, Newton was the first person to comprehensively explain how and why the solar system operated.