By Rebecca Smith

1. Outline the historical development of models of the universe from the time of Aristotle to the time of Newton…… By Rebecca Smith

2. Scientific Background • Astronomy is the oldest science about 1000 BC. • Used by Priests and Holy Men for planting cycles and organisation of religious celebrations • First models developed with NO Formulas NO technology and a lot of uncertainty

3. Timeline of major models… Aristarchus (312 – 230BC) Nicholas Copernicus (1473-1542) Johannes Kepler (1571-1630) Isaac Newton (1643-1727) Tycho Brahe (1546 – 1601) Galileo Galilei (1542 – 1643) Aristotle (384-322 BC) Claudius Ptolemy (AD 150)

4. Definitions • Geocentric– universe where the Earth is placed at the centre • Heliocentric – universe where the sun is placed at the centre. • Parallaxeffect -a change in displacement of an object taken from two different frames of reference and can be measured by the angle of inclination of the two lines.

5. OVERVIEW OF ARGUMENTS FOR - • incorporation of heaven (Christians) • Consistent with other models • Easy to understand • Ease for measurements AGAINST - • Too complex • Too simplistic • No mathematical evidence • Summary • Consistent with other models • Only relative measures made • Religious views

6. Aristarchus ARISTOTLE • FEATURES : • Earth to be flat, spherical universe with heavens above. • Geocentric model • ARGUMENTS : • gaining Christian approval due to incorporation of heavens • becoming to complex with additions and many modifications and having no real impact on scientific advances • in astronomy but rather acted more as a summary. • Unfathomable nature of infinity • could not detect a parallax effect, and could not explain universal changes. FEATURES : • First heliocentric model • Developed idea that earth rotated on axis once a day giving illusions of astronomical features. ARGUMENTS : • Disliked due to so different from widely accepted Aristotle. • Main

7. Claudius Ptolemy FEATURES : • Compiled an extensive summary of all the Greek's previous studies on astronomical physics. • This model reliably predicted positions of planets, was geocentric, showed the earth to be at rest and explained the motion of planets as the combination of perfect circles. ARGUMENTS : • The model was advantageous as it provided useful predictions to both past and present planetary positions and allowed was consistent with previous models, however the model had no mathematical evidence, • was very complex and measures were found to be relative not absolute. RECOMMENDATIONS : Whilst the Ptolemy model can not be used to make accurate mathematical calculations about the universe, it is a very effective model in providing a summary of all previous astronomical theories, and assists one in learning about the history of models of the universe.

8. Nicholas Copernicus FEATURES : • supported the Aristarchus heliocentric model, where the stationary sun was in the centre of the model with everything else in the universe revolving around it. ARGUMENTS : • ease for mathematical calculations • simpler model. • church and government had the major objections to this model as there was no account for the heavens unlike the Aristotle model. • The inadequacies of the model. As only a change of reference was shown RECOMMENDATIONS : Copernicus` model is essential in the study of the history of models of the universe. Whilst it was criticised for only being a change in the frame of reference, this change makes this model one of the most accurate first models ever developed. This model is definitely recommended as an important discovery.

9. Tycho Brahe FEATURES : • studied and plotted the night sky in extensive detail, this was seen as an incredible achievement as he managed to do this with no aid of a telescope. • combination of both geocentric and heliocentric models • Due to lack of technology, Brahe could not show a parallax effect, • FEATURES : • Tycho Brahe` talented mathematician assistant, • developed mathematical laws to determine the movement of planets. • He discovered; that planets moved in ellipses, known as the Law of ellipses and the Law of Periods. • ARGUMENTS : • Due to Kepler being a protestant in Austria, his theory was able to be voiced openly with little risk, Rome's arguments however were still the same as they were with the Copernicus model. Johannes Kepler

10. Galileo Galilei FEATURES : • believed in the Copernicus model. • Galilei was a brave man who made his own telescope and became the first person to point one at the night sky. • he disproved Ptolemy's geocentric model. ARGUMENTS : • Roman Church views Galilei left a great legacy even though he had to fight many arguments as a result of his findings. Isaac Newton FEATURES : • The physics that the great Isaac Newton (1643 – 1727) brought to the world of Astronomy allowed the proof of a heliocentric model. • summarising a long history of developments. • Newton's major law which aided this include the Law of Universal Gravity, which describes gravity as a force which exists between two masses, with particular effect on large masses such as planets. • From this law Kepler's laws could be derived and therefore the explanation for why planets orbit in ellipses not circles was found. This supported a parallax effect and allowed the heliocentric model to be supported.

11. Recommendation When recommending the best astronomical model of the universe it is difficult to choose which model is the most efficient. Newton`s model can be suggested as the best as there is mathematical evidence and workings that prove aspects of the universe. However his model could only be produced with the strong foundation of models previously developed. Therefore when studying the universe, Newton’s model is most efficient however all models specifically Ptolemy's and Copernicus` (mentioned previously) are found to be productive in providing information on the development of models of the universe.