Section I - Items illustrating the background to the problem.

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1. Portrait of Nicholas Copernicus (1473-1543) who many regard as the founder of modern astronomy. Born in Poland he studied in Cracow and Bologna. Though made without the aid of a telescope, his careful observations together with those of others and his physical intuition, lead to a revolution in our understanding of the mechanics of the solar system. The new heliocentric theory which he propounded maintained that the Earth moved around the Sun once per year and rotated on its own axis once per day. (Univ. of Nicholas Copernicus, Torun)
Tycho Brahe 2. Tycho Brahe (1546-1601), the greatest of the pre-telescopic astronomers, whose precision observations made it possible to test the new heliocentric hypothesis and allowed his successor, Johannes Kepler to derive his famous laws of planetary motion.
Tycho's observatory 3. Tycho's Observatory built in 1584 at Uraniborg in Denmark.
Johannes Kepler 4. Johannes Kepler (1571-1630) who formulated a set of laws which could be expressed in simple equations to describe the motions of the planets about the Sun. His famous third law, stated that the the square of the period of a planet is proportional to the cube of its distance from the Sun. As the periods of all the planets were known, it was only necessary for the distance of one of them to be measured to derive the distance from the Sun of all. (High Altitude Observatory)
The Rudolphine Tables 5. The Rudolphine Tables compiled by Kepler and Tycho which were published in 1627. These tables gave the positions of the planets with an accuracy many times better than any previous rivals and were instrumental in establishing the superiority of the new heliocentric picture of the solar system. They were named after the Emperor Rudolf II who commissioned the calculations on which they were based in 1601.
Orrery by Gilkerson 6. An Orrery by Gilkerson These models of the solar system were designed to illustrate the relative simplicity of the Copernican system and to convince people of its authenticity. They received their name from Charles Boyle, 4th Earl of Cork and Orrery, for whom the first such device was made in 1705 by John Rowley.
Galileo 7. Galileo (1564-1642) whose defence of the Copernican heliocentric solar system lead to a bitter conflict with the establishment and the Catholic Church. Galileo's observations of spots on the Sun and craters on the Moon, made with the recently invented telescope, showed them not to be the flawless heavenly bodies people had previously believed. (Courtesy of the High Altitude Observatory)
Frontispiece to Opere di Galileo Galilei 8. Frontispiece to Opere di Galileo Galilei (1656) The works of Galileo which gave robust support for the Copernican system.
Sir Isaac Newton 9. Sir Isaac Newton (1642-1727) was one the greatest scientists of all time. His theory of universal gravitation provided the physical and mathematical basis for our understanding of planetary motions. He was able to show that the force of gravity that draws a falling apple to the ground is the same force that holds the Moon in its orbit about the Earth and the planets in their orbits around the Sun. This painting by Sir Godfrey Kneller shows Newton in 1702 shortly before he became President of the Royal Society. (Courtesy of the National Portrait Gallery)
Principia Mathematica 10. Principia Mathematica (1687) Newton's masterpiece; the most important treatise in the history of science. In this book, Newton showed how mathematics could be used to describe the behaviour of the universe; an idea which is fundamental to modern science. Here, he postulated his laws of motion and of universal gravitation which provided the basis of our understanding of the mechanics of the solar system for the next two centuries. It was not until Einstein's theory of General Relativity was developed that it became apparent that Newton's theory represented a simplification of the true situation.

Last Revised: 2009 November 18th