2-5 Renaissance “naissance” = “birth”. The belief that the cosmos is ultimately understandable slowly emerges again. Revival of art. The Birth of Venus, Botticeli, 1485. Rediscovery of perspective (and geometry). Delphic Sybil, Michelangelo,1510 - 1512. Rediscovery of light.
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The belief that the cosmos is ultimately understandable slowly emerges again
The Birth of Venus, Botticeli, 1485
Lady with an ermine, Vinci
The creation of the planets, the Sun and the Moon, Michelangelo
Middle Age bas-relief
Figures hardly stick out of the stone
Perfect knowledge of the human body
Magellan’s travel around the Earth: 1519
Early champion of the heliocentric model: “the Sun, not the Earth, is the centre of the universe”
In the existence of inhabited planets
That the universe is infinite
But before all, dreamt of a radical reform of Christianity
1600: Bruno was burnt by the Holy Inquisition
Often portrayed by scientists as a martyr of science
Priest interested in mathematics and astronomy
Understood that stellar parallax is not observed because stars are too far
Goal: to predict the position of the planets
Very complex calculations !
A overtakes B. What does A see of B?
B seems to be moving backward
Now B overtakes A. What does A see of B?
B is moving forward
A: “B has moved back and forth”
Like in a car race, the Earth is sometimes overtaking Mars, giving us the impression that Mars is moving backward
Mercury orbits at a higher speed than Mars
He did not claim his model described the actual motion of the Earth. It was just a mathematical trick.
His model: no better accuracy than Ptolemy’s => was not widely accepted until more than a century
They argued that if the Earth were rotating, we would feel its motion
Anyway astronomers had no telescope…
Born three years after Copernicus’ death
Found that the predictions of Ptolemy’s model were inaccurate
Tycho measuring the altitude of a celestial object, 1587
He believed in a modified geocentric model
All planets orbit around the Sun but the Earth!
Brahe had to find a new job…
He became court astronomer to the Emperor Rudolf of Bohemia, in Prague, Austria
There he met a diligent assistant: Johannes Kepler
Became convinced that all the planets are actually orbiting the Sun
When Brahe died, Kepler got full access to Brahe’s records, that he studied for more than 20 years
At the age of 38, he finally published his first results
Position of the Sun
An ellipse which does not differ much from a circle is not “very eccentric”
e is close to zero
An ellipse which is very elongated has an eccentricity close to 1
Caution: same orbit seen from two different points of view
Speeds up as it comes closer to the Sun
Slows down as it moves away from the Sun
P: orbital period (time needed for one revolution), in years
a: semimajor axis, in AU
a3 = P2
Closer to the Sun
He could estimate the distance from each planet to the Sun (a), in AU
This was a nice model, but yet it did not explain why the planets were orbiting the Sun
Meanwhile, a genius was at work in Florence, Italy…