2. [60 points total] Greek Cosmology: (a) [15 points, 1 para.] How did the Greek
ID: 3308548 • Letter: 2
Question
2. [60 points total] Greek Cosmology: (a) [15 points, 1 para.] How did the Greek model of cosmology evolve over the millennia and set the stage for the modern scientific revolution which began in the middle ages? (b) [10 points] Who was the Greek philosopher who first proposed that solar/lunar eclipses respectively arose from the Moon's and Earth's shadows? Please explain their theorv in 3 sentences. (c) [15 points, 1 para.] Explain the Pythagoras system of numbers (integers, masculine/feminine) and the concept of perfect numbers and perfect shapes. (d) [20 points,1-2 para.s] Summarize how planetary retrograde motion was explained in the model of Ptolemy. Comment on how the concept of perfect eternal circular motions in the geometric universe conceived by Ptolemy, Aristotle and Plato delayed scientific progress towards our understanding of the Sun-centered solar svstemExplanation / Answer
1)
GREEK MODEL OF COSMOLOGY
Anaxagorian Universe - (5th Century B.C. Greek philosopher Anaxagoras)
He believed that the original state of the cosmos was a mixture of all its ingredients which existed in infinitesimally small fragments of themselves. This mixture was not entirely uniform, and some ingredients were present in higher concentrations than others, as well as varying from place to place. At some point in time, this mixture was set in motion by the action of “nous” (mind), and the whirling motion shifted and separated out the ingredients, ultimately producing the cosmos of separate material objects, all with different properties, that we see today.
Atomist Universe - Later in the 5th Century B.C., the Greek philosophers Leucippus and Democritus founded the school of Atomism, which held that the universe was composed of very small, indivisible and indestructible building blocks known as atoms (from the Greek “atomos”, meaning “uncuttable”). All of reality and all the objects in the universe are composed of different arrangements of these eternal atoms and an infinite void, in which they form different combinations and shapes.
Aristotelian Universe - The Greek philosopher Aristotle, in the 4th Century B.C., established a geocentric universe in which the fixed, spherical Earth is at the centre, surrounded by concentric celestial spheres of planets and stars. Although he believed the universe to be finite in size, he stressed that it exists unchanged and static throughout eternity. Aristotle definitively established the four classical elements of fire, air, earth and water, which were acted on by two forces, gravity (the tendency of earth and water to sink) and levity (the tendency of air and fire to rise). He later added a fifth element, aether, to describe the void that fills the universe above the terrestrial sphere.
2)
Anaxagoras (around 500 and 428 B.C) was the first Greek philospher who correctly explained that a solar eclipse occurred when the sun cast the shadow of the moon on Earth.
3)
Pythagoreans divided integer numbers into following categories-
(i) Perfect square (like 1, 4, 9) - these corresponding the number of dots which can be arranged in a perfect square.
(ii) Triangular (like 1, 3, 6, 10) - these dots can be arranged into regular triangles.
(iii) Oblong (2,6, 12) - these dots can be arranged into rectangles.
Along with describing numbers in terms of math and geometry, the Pythagoreans also described them in terms of non-numerical traits. Odd numbers were masculine, and even numbers were feminine. Sum of two and three, five represented marriage.
4)
Retrograde motion is an APPARENT change in the movement of the planet through the sky. It is not REAL in that the planet does not physically start moving backwards in its orbit.
Ptolomy's model and Aristotal model of the solar system was geocentric, where the sun, moon, planets, and stars all orbit the earth in perfectly circular orbits. This model can't explain retrograde motion.
Copernicus (16th cent) proposed a heliocentric (Sun centred) model for the universe. This is present model and it explain the retograde motion of star. During orbital motion star also do spin motion about its own axis. Spin motion is the key factor due to which star appear in retograde motion.
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