Astronomy Timeline How theory develops and changes over time as new technology allows for more accurate observations.

Plato ( B.C) argued that the sphere and the circle were perfect shapes because of their symmetry The heavens being the creation of the god would have to be “perfect” The heavens were assumed to contain spheres in uniform (constant speed) and perfect, circular motions and earth was the center of motion (Geocentric).

Founded in 283 BC, by 300 B.C. the Library of Alexandria is accepted as the leading center of knowledge, housing more than half a million books (scrolls of parchment or leather and clay tablets). The library of Alexandria held over half a million documents from Assyria, Greece, Persia, Egypt, India and many other nations. Over 100 scholars lived at the Museum full time to perform research, write, lecture or translate and copy documents.

280 BC Aristarchus Alexandria Egypt Introduces a competing theory Suggests the Earth revolves around the Sun(heliocentric). However still believes in the idea that all planets are perfect spheres and travel around the sun in perfect circular orbits and the star are fixed on great celestial spheres.

240 B.C. Eratosthenes of Cyrene (now Shahhat, Libya) He measures the circumference of the earth with surprising accuracy. The importance of this is to realize that The ancients believed in a spherical earth. However out of the Dark ages and into the middle ages, Western Europe believed that the earth was flat.

140 AD Ptolemy - Geocentric theory Writes the Almagest which tells us that the Western European world has accepted the theory that the Earth is the center of the universe. Stars are fixed on celestial spheres. All the planets and the celestial spheres move in perfect circular motion.

140 AD Ptolemy - Geocentric theory Most importantly, He tires to explain the motion of Mars and other planets using epicycles.

415 A.D. The final destruction of the library of Alexandria, along with the loss of most of the knowledge stored there.

AD Age of Darkness An age of very little intellectual advancements due to fall of Roman empire, barbaric intrusions and warfare.

(Ferdinand Magellan 1522 circumnavigates the globe 18 of 237 survive) 1492 Christopher Columbus Sails the ocean blue

1543 Copernicus –Writes De Revolutionibus which re introduces the competing theory to the geocentric theory Heliocentric theory. –Believes the sun to be the center of the universe Stars are fixed on celestial spheres. All the planets and the celestial spheres move in perfect circular motion.

1543 Copernicus Most importantly, he introduced a competing idea for the Motion of Mars.

1551 Leonard Digges Invents the theodolite and, from the writings of his son, it was possibly used as a telescope. Which would make Leonard the inventor of the first telescope.

1576 (G is 12) Thomas Digges –Comments on his father’s writings (1 st telescope?) –Puts the heliocentric model into stars of infinite space and NOT celestial spheres. To do this, he must have taken astronomical measurements. Did he use the theodolite to study the skies? None of his writings suggest that he did. So neither he or his father is given credit for inventing the telescope.

1577 (G is 13) Tyco Brahe- Spends 20 years of his life studying and measuring planetary movements and motion of stars. Observes a comet over a year’s time. Using Parallax, Tyco proves through observation, measurements and mathematics that Thomas Digges was correct. The stars are NOT fixed on celestial spheres.

1600 (G is 36) Johannes Kepler –Uses Tyco’s data to prove that the planets revolve in elliptical orbits. NOT perfect circular orbits.

It is around this time that the geocentric Theory begins to fall apart due to accurate observations made possible through improvements of the tools used to make astronomical measurements. Stars are no longer fixed on crystal spheres. Planets travel in elliptical orbits and not perfectly circular orbits.

1608 (G is a famous professor at university of Pedua 44) Hans Lippershey is officially recorded to have invented the telescope.

1609 Galileo –Invents a new and improved model of Hans’ telescope –Introduces a law of motion called inertia

1609 Galileo Most importantly, the discovery of the moons orbiting Jupiter proves that the earth is NOT the center around which all objects orbit.

Galileo was a remarkable man. After stating that the Sun was the center of our universe, the church held him under house arrest. He died under house arrest in such great pain from arthritis that even his guards pleaded with their superiors to give them another assignment. Though Galileo recanted his theory and proofs, he continued to study the planets and sun. He died knowing that what he knew to be true was being suppressed and he could do nothing about it. He must have wondered on his death bed, “How long before they accept the truth?”

Good reading resources Galileo's Daughter: A Historical Memoir of Science, Faith, and Love by Dava Sobel The Scientists: A History of Science Told Through the Lives of Its Greatest Inventors. By John Gribbin