Philosopher's Contributions



Approx. 384 BC - Approx. 322 BC

Thought that the motions of planets and stars were perfect circular movements
Thought that the orbits would go on forever
that the planets and stars were perfect spheres though Earth itself was not


310 BC - 230 BC

Heliocentric Model:
Earth rotates on axis
Moon < Sun
Sun remains within the midst of solar system
Earth orbits sun
Concept was disbelieved + declined of existence
Archimedes (Greek mathematician), Plutarch (Greek biographer) and Sextus Empiricus (Greek philosopher) formed reference of Aristarchus’ concept, as well as proposing, if theory is candid, approaches toward universe (including scale + size) will be altered
Diameter of Earth’s shadow x2 diameter of moon
Moon + sun each 2 degrees in angular diameter
Time of quarter moon, angular distance between moon and sun is 87 degrees
Sun was considered to be 18 and 20x from Earth as opposed to moon
Gained values for scale + size of moon and sun
Hipparchus and Ptolemy altered Aristarchus’ initial calculations to obtain an accurate sizing of moon and sun
Aristarchus was considered to have founded later concepts regarding universe + solar system + orbits of planets + sizing of heavenly bodies
Theory formed: approximately 310-230 BC


100 AD - 168 AD

Earth was the center of the universe
Astronomer and mathematician
Earth was the center of the Universe.
He was able to combine what he saw of the stars' movements with mathematics, with geometry, to predict the movements of the planets.
he worked out that the planets must move in epicycles, smaller circles, and the Earth itself
Made the math work for his predictions
To prove his mathematical predictions true, he worked out that the planets must move in epicycles, smaller circles, and the Earth itself moved along an equant (the was not true)


1473 - 1543

Well over a thousand years later, Nicolaus Copernicus came up with a radical way of looking at the Universe. His heliocentric system put the Sun (helio) at the center of our system. He was not the first to have this theory. Earlier starwatchers had believed the same, but it was Copernicus who brought it to the world of the Renaissance and used his own observations of the movements of the planets to back up his idea. His ideas, including the revelation that the Earth rotates on its axis, were too different for most of the scholars of his time to accept. They used only parts of his theory. Those who did study his work intact often did so in secret. They were called Copernicans.

Tycho Brahe

14 December 1546 - 24 October 1601

1853 : Danish astronomer Tycho Brahe offered concept (compromised model)
Portion of concept: derived from initial Ptolemaic system - earth remains within midst of universe, whilst sun + moon orbits earth
Second portion of theory: supplemented Copernicus’ concept (all planets orbited sun)
Formed compromised model, since in Copernicus’ and Ptolemy’s theory; all stars remain within an unchanging sphere that revolves Earth, and Tycho announced phases of Venus
Concept: earth within midst of universe + sun and moon orbit earth + remaining planets orbit sun

Galileo Galilei

15 February 1564 - 8 January 1642

Devised a telescope that could enlarge objects up to 20 times
Proved the truth of the Copernican system of heliocentrism
Brilliant student with a genius for invention and observation/
Opposed to what Aristotle taught
had his own ideas on how motion really worked
devised a telescope that could enlarge objects up to 20 times. He was able to use this telescope to prove the truth of the Copernican system of heliocentrism.
He published his observations which went against the established teaching of the Church. He was brought to trial and, although he made a confession of wrongdoing, he was still kept under house arrest for the rest of his life.

Kepler the New Astronomy

27 December 1571 - 15 November 1630

German astronomer
Formed major laws regarding planetary motion:
1) planets orbit sun within ellipses
2) time required to transverse all arcs of a planetary orbit involves = proportional to area of sector between planetary body & arc:arc ---- “Area Law”
3) relationship : squares of planet’s periodic times + cubes of radii of orbits ---- “Harmonic Law”
Kepler considered his astronomical developments as “celestial harmonies” that were labelled to reflect God’s arrangement of universe
Copernicus’ model was transformed into a dynamic system that involved planets that were forced to motion as well as orbit the sun within ellipses
Kepler’s physical astronomy forced arising dilemmas for further universe development


4 January 1643 - 31 March 1727

Continued to expand the work of Galileo- relationship between energy and motion
Invent the 3 laws of Motion
Produced convincing proof to support heliocentric theory
Said that the sun exerted a constant pull which caused the the earth to rotate around the sun