The Copernican Revolution 1540 - 1690 started by Nicolaus Copernicus 1473 -1543

Astronomy in the Renaissance However, problems remained: Could not predict planet positions any more accurately than the model of Ptolemy Could not explain lack of parallax motion of stars Conflicted with Aristotelian “common sense”

Copernican System Copernicus concluded that the sun, not the Earth, was the center of the solar system. This is known as heliocentric - sun centered. This was a radical departure from Aristotle's view. Although Copernicus was a priest, his position was troubling to the Church. His idea was published in 1543 in De Revolutionibus - on his death bed.

Retrograde Motion The heliocentric idea was able to explain observations of the planets. The idea of retrograde motion could be explained without the use of epicycles. Copernicus' idea of uniform circular motion did have its problems. There were observed variations in the movement of the planets. The uniform circular motion which Copernicus assumed, was not correct so he kept epicycles.

Tycho Brahe 1546 - 1601 Funded by the king of Denmark built the first modern observatory Uraniborg (Sky Castle) Tycho Brahe made the most accurate visual observations of the planets. His observations allowed for precise position predictions. His discovery of a 'new star' was more proof against Aristotle's perfect and unchanging starry sphere. However, he did believe the Earth was stationary because he could not measure parallax of the stars.

Tychonic Universe Not detecting parallax, Brahe developed a complex scheme. He made the Earth fixed, around which the sun and moon circled. The planets then rotated around the sun. His goal was to publish an improved Alfonsine Tables based on his Tychonic Universe idea.

Brahe's Model Tycho's idea is represented in this figure. The revised Alfonsine Tables would be called the Rudolphine Tables. This was to honor his new patron Emperor Rudolph II.

Kepler 1571 - 1630 Kepler was appointed to succeed Brahe as imperial mathematician by Rudolph II and was able to transfer Brahe's extremely accurate observations into the planetary laws of motion which bear his name. Kepler was an extremely religious man and deeply troubled in his personal life but this did not stop him from his great discoveries of planetary motion.

His model did not work. Kepler's Model Kepler was trying to know the mind of God. He was convinced that geometry was the mind of God, which held the answer to the motion of the planets. He placed the sun at the center and invoked the regular solids using one for each planet's orbit. His model did not work.

Elliptical Orbits Ultimately, Kepler had to abandon his belief in geometry and use the data from Brahe to determined his three laws of planetary motion. (1) All planets orbit the sun in an elliptical orbit. (2) A planet will sweep out equal areas in equal time. (3) The Harmonic Law states that the period squared of a planet's orbit is equal to its distance from the sun cubed.

3rd law T2 / r3 = k T is the period in years “r” is the radius in Astronomical Units (AU) T2a / r3a = T2b / r3b

Kepler's Orbits Retrograde Motion *Kepler's laws described planetary motion but did not explain what caused it. *He finally completed the Rudolphine Tables which allowed for accurate prediction of planetary position. *Kepler's accuracy was from 10 to 100 times better than previous tables. Retrograde Motion http://projects.astro.illinois.edu/data/Retrograde/index.html

Galileo 1564 - 1642 Galileo Galilei was the first scientist to write directly to the people. It was common practice for scholars to write in Latin but Galileo also wrote popular books in Italian. Galileo invented the astronomical telescope (bringing images 30 x closer), although a lensmaker in Holland made the first telescope.

Galileo's Telescope Galileo observed Jupiter in 1610. His telescopic observations revealed an imperfect moon, the Milky Way was made of stars, and Jupiter had four objects orbiting it and these observations ended Aristotle's incorrect views on astronomy. These views also got Galileo in trouble with the church.

Evidence for the Heliocentric Model Venus undergoes full phase cycle Þ Venus must circle Sun

Galileo To challenge Aristotle was to challenge the authority of the Church. The Church could not afford anymore attacks on its authority. Galileo was placed under house arrest until he died. His trial caused many questions through the years and in 1992 an indication of innocence was implied by the Church.

Isaac Newton 1642-1727

Isaac Newton was born the year Galileo died. He made major advances in mathematics, physics, and astronomy. He pioneered the modern studies of motion, optics, and gravity and discovered the mathematical methods of calculus. It was not until the 20th century that Newton’s laws of motion and gravity were modified by the theories of relativity.

Birth of Modern Astronomy Here we see the time line showing the transition from the ancient astronomy of Ptolemy to the birth of modern astronomy.