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384 BCE
Aristotle (384-322 BC)
Aristotle, a student of Plato, supported Pythagoras' idea that the Sun, Moon, planets and stars were rotating around the Earth.
Each of these 'celestial objects' were in their own sphere in fixed positions around the earth, rotating in perfect circular motion. -
Period: 384 BCE to
Ancient Models of the Universe
Our Sun is just one star in the galaxy and ours is just one galaxy in the Universe:
- outline the historical development of models of the Universe from the time of Aristotle to the time of Newton. -
Period: 380 BCE to 1500
Geocentric Universe
The GEOCENTRIC model of the universe first proposed by Aristotle c.384BC, held up for almost 2000 years - the main reason for this being the lack of technology at the time to prove otherwise. -
310 BCE
Aristarchus (310-230 BC)
Aristarchus, based in Egypt, was the first astronomer to propose that the Sun was at the centre of the universe. His basis for doing so was that it made more sense for the largest object the be placed at the centre. He had already estimated the relative sizes of the celestial bodies and concluded that the Earth was much smaller than the Sun. His ideas were good, but not detailed enough and without sufficient evidence the more popular geocentric model remained in favour. -
200 BCE
Apollonius (265-190 BC)
Apollonius supported the geocentric model of the time, although it could not account for the sometimes 'retrograde' motion of the planets where they seemingly moved backwards in the night sky for a time before continuing on their path. He developed the idea of "epicycles" to account for retrograde motion - where the planets followed their own circular path as they moved around in their circle around the Earth. -
199 BCE
Hipparchus
Hipparchus further refined Apollonius' model to account for the observation that the sun was further away from Earth at some times of the year than others.
To do this, he placed the Earth slightly off-centre in the geocentric model and kept the epicycles. It should be noted that during the course of his work involving observations of celestial bodies, Hipparchus developed the system of stellar magnitudes that astronomers still use today. -
140
Ptolemy (100-170 AD)
Ptolemy further modified Aristotle's geocentric model of the universe by developing a complex model of based on concentric circles. The model was so complex, building on previous works and including epicycles within epicycles - in hindsight it's a mess!
At the time though it was based on evidence and mathematics - and it was so good at predicting the future positions of celestial bodies that it could not be disputed. The Church also adopted this theory, giving it even more credence. -
1543
Copernicus (1473-1543)
Copernicus developed a model of the universe that had the Sun at the centre - a heliocentric model that was able to explain the apparent retrograde motion of the planets in a much simpler way than previous geocentric models. He still had the stars in a fixed outer orbit, but around the sun rather than Earth. His model was not better at predictions than Ptolemy's, and it suggested parallex movement of stars which could not be detected at the time, so his model didn't gain much popularity. -
Period: 1543 to
Heliocentric Universe
As technology improved and more scientific data was collected, the HELIOCENTRIC model of the universe eventually won over previous geocentric models. It was a struggle to do so however, given that the geocentric models were so well ingrained in people's minds as being true. Geocentric models were also strongly supported by the Church, in fact anyone who even dared to suggest otherwise was dealt harsh punishment as it was considered blasphemy. -
1580
Tycho Brahe (1546-1601)
Tycho Brahe made observations of the night sky, plotting the positions of thousands of stars. Even though telescopes had not yet been invented, he was able to do so with remarkable precision at the time - because he invented his own instruments that allowed him to plot position within 30 arc seconds of accuracy.
The benchmark at the time was 15 arc minutes. -
Tycho Brahe - Geo-Helio-centric model (!)
Tychoe Brahe proposed a different model - a complicated mix of both geocentric and heliocentric ideas. He had the sun and the moon still rotating around the earth - but he then had all the other planets rotating around the sun. He then had the stars still in a fixed sphere rotating around the whole system, with the Earth at the centre. His reasoning was that he just could not accept that the earth was moving, and at the time there was no technology available to prove that it was. -
Johannes Kepler (1571-1642)
Kepler was a mathematician and Brahe's assistant. After Brahe's death, Kepler inherited all of his data and analysed it. He favoured Copernicus' model of the universe with the sun at the centre, but instead of planets orbiting in prefect circles, he proposed that the orbits were instead elliptical. Kepler didn't have access to any better technology than Brahe, but he didn't need to - he analysed data already available and proposed a model of best fit, being elliptical maths (not circular). -
Galileo Galilei (1564-1642)
Galileo did not invent the telescope, but he was the first to use it for observation of celestial bodies. He discovered the four largest moons of Jupiter, showing their orbit around the planet.
He also discovered that Venus has phases just like the moon, sometimes 'disappearing' behind the sun. These observations and Kepler's maths, were sufficient evidence to disprove the geocentric models in favour of Copernicus' heliocentric model. The Church put him under house arrest for blasphemy.. -
Isaac Newton (1642-1727)
Newton invented calculus and developed scientific theories of motion. He was the one to apply the laws of gravity not just on Earth, but also to the moon and the other planets.
Newton's maths can be used to derive Kepler's equations of elliptical motion. It was Newton's maths years after his death that ultimately led to the discovery of Neptune - when Uranus' motion didn't fit the model, if Newton's maths was right then there had to be something else contributing.
