NATS1745 - chapter 3

•    Greece was broken up into innumerable valleys and islands. There could be no over-arching control system. Instead, each region developed its small own city state, or polis, the Greek word that gives rise to ‘politics.’ And trade between the city states was in the hands of independent merchants. So Greece developed the world’s first middle class culture.  With fluid funds, the prosperous Greek middle class had time on their hands - and freedom to do what they liked with it. The fundamental geography and decentralized rule of Ancient Greece allowed for an intellectual freedom that led to a revolution in scientific thought

• ·        
• Considered the "Father of
• Science" for attempting to find explanations for natural phenomena that
• didn't involve the gods. Thales apparently made the first accurate prediction
• of a total eclipse of the Sun, on May 28, 585 BC.

• ·        
• Set the Earth afloat in
• air.  He described how the earth, moon,
• sun and stars are organized stars. He set the earth afloat-> meaning that he
• proposed that we are not standing on a ground that stands infinitely beneath
• on. We are standing on a disk in space.

• ·        
• According to legend, when he
• discovered that musical pitch is determined by the length of the instrument, he
• realized : the Universe is a cosmos ( a harmonious system that obeys knowable
• laws).

• ·        
• He taught that all celestial
• motion is perfectly circular, and that the Earth is a sphere

• ·        
• Pythagoras proposed that the
• Earth is round.

• ·        
• Ships gradually disappear on
• the horizon bottom – first

• ·        
• Earth's shadow on the eclipsed
• moon is always round

• ·        
• When you travel North or South,
• the constellations rise and set more rapidly than they would if Earth was flat

• ·        
• He believed that the earth
• moves.

• ·        
• explains why all celestial
• bodies rise and set

• ·        
•  no need to say that the moon has a monthly
• component and a daily motion, as well as the sun

• ·        
•  the movement of celestial bodies becomes far
• less complex

• ·        
•  earth rotates once a day : but Philolaus
• thought the earth moves through space once a day

• ·        
•  according to him, the central fire is never
• seen

• ·        
•  his argument for that was that only one side
• of the earth is inhabited

• ·        
•  and that side never faces the fire

• ·        
•   Philolaus also proposed that between earth
• and central fire there is anti earth ( never seen ) and the purpose of it  was as a protective shield

• ·        
• He set Earth spinning daily
• around its own axis. He had all the planets orbit around the earth as well.

• ·        
• He placed Mercury and Venus in
• orbit around the Sun to explain the Sun - centered appearance of their motion
• and their brightness changes

• ·        
• Aristarchus used Earth's shadow
• on the eclipsed moon to measure the Moon's size relative to Earth's.

• ·        
• Used the angle in the sky
• between the Sun and quarter Moon to measure the Sun's distance and size
• relative to the Moon's

• ·        
• His measurements weren't
• accurate, but he correctly deduced : the Sun is much larger than Earth, and
• Earth is larger than the Moon

• ·        
• This led him to propose a
• heliocentric model of the Universe, with only the Moon in orbit around Earth (
• owing to the Moon's  straight night - to
• - night path around the sky)

• ·        
• Planets display both direct (
• forward )motion ( W to E ) and retrograde ( backward) motion ( E to W).

• ·        
• From Earth the speed of the
• planets look non-constant is what we see

• ·        
• The brightness also looks
• non-constant

• ·        
• All celestial bodies are
• perfect unblemished sphere

• ·        
• Constant motions

crystal orbs

• ·        
• Came up with double sphere
• model to try and explain

• ·        
• The Earth is at center

• ·        
• Made of ether quintessence

• ·        
• The Earth is fixed at the
• centre of the Universe ( geocentric). 
• All matter in the terrestrial realm is composed of four elements :
• Earth, water, air and fire.

• ·        
• He used Eudoxus’ model

• ·        
• They are circular all the
• crystal orbs are spheres

• ·        
• They have constant speed
• through space  

• ·        
• He said [ believed earth is
• fixed] surrounding our entire universe is one enormous crystal orb that [spins
• once a day,], and it explains why the sun rises and sets everyday.

• ·        
• Prime mover that constantly
• pushes on us

• ·        
• Aristotle taught comets must be
• atmospheric phenomena because they don't appear eternal, therefore they can't
• be celestial bodies.

• ·        
• Appolonius upgraded the Eudoxan
• planetary model to the epicycle model. 
• The model still required that the planets still have constant circular
• motion around fixed earth, but he was able to come up with a new way that
• involved the movement of the planets. 
• All motion is circular and with constant speed. Deferent circle, planet,
• earth, epicycle. All motion is circular and constant.

• ·        
• Changing speeds of the planets
• in the sky- the motion cancels out so slower

• ·        
• The changing brightness of the
• planets in the sky- when a planet goes retrograde it is at is closest position
• to Earth at the bottom therefore brighter

• ·        
• And retrograde motion – is that
• when the planet comes around the bottom of the epicycle them motion is opposite
• to the direction of the epicycle

• ·        
• Meaused the circumference of
• the Earth

• ·        
• Used a scythe

• ·        
• Measured the length of the
• shadow

• ·        
• Hipparchus checked out the
• Moon’s motion in extraordinary detail, which meant he could predict eclipses
• with more confidence than anyone before him. 
• The complicated gearing of the Antikythera Mechanism even mimics the way
• the Moon’s speed changes over a cycle that lasts nice years.  The way in which it displayed the moon is
• very advances, and seems to be based on a theory of the Moon developed by
• Hipparchus.

• ·        
• Observed the 20 minute
• difference between time between the solstices

• ·        
• Causes the suns position in the
• sky to shift by a tiny amount by year to year

• ·        
• Zodiac signs are different than
• in the past because the Sun's position relative to the constellations changes.

• ·        
• A Roman statue of Atlas carries
• a copy of Hipparchus’ Farnese globe - his incredibly accurate star catalogue -
• on his shoulders. Brad Schaefer, a astrophysicist and historian holidaying in
• Italy, stumbled across the globe in the National Archeological Museum in Napes.
• He has dated the original to around 125 BC - contemporary with the time when
• Hipparchus lived.  The only astronomer
• who was mapping the stars at the time was Hipparchus.

• ·        
• Ptolemy drew together all of
• the Greeks’ knowledge of the heavens in a 13-volume masterpiece called the
• Matematike Syntaxis [ Mathematical Treatise], better known today by its later
• Arabic title, the Almagest.

• ·        
• It would be constant that is
• the definition of the equant point

• ·        
• Conflict is that the equant
• point forces a planet to speed up and slow down

• ·        
• Speed up when far from equant
• point slow down when close to equant point

• ·        
• to explain why mercury and
• venus always appear close to the sun in the sky, while the other planets don't

• ·        
• Ptolemy placed the planets in
• order of their decreasing apparent speed. The order of the planets was correct,
• but the Sun and Earth were incorrectly switched

• ·        
•   By assuming no space between adjacent orbits,
• Ptolemy estimated the " Universe's size to be ~ 20,000 Earth radii (
• actual 260,000). Despite the error, this proved the enormous distance to the
• stars