Plato: Saving the Appearances

• Plato's problem of "saving the appearances" explores how Plato constrained the Greek model of universe
• Plato lived from 427-347 B.C.

Apparent Planetary Motion

• The idea centers around observing how planets appear to move
• Apparent planet is on Epicycle
• Epicycle is offset from the center Q
• Earth is in the center
• Deferent extends from Earth around the epicycle

General Beliefs in Planetary Motion

• Stars rotate from east to west, eventually returning to their original location

Plato and Saving the Appearances

• Plato was an ancient Greek Philosopher
• Plato was a famous student of Socrates and a teacher of Aristotle
• Plato proposed the irrational motion of planets due to movement in circular tracks

Plato and Saving Appearances

• Plato's idea of planetary motion includes orbits within orbits
• Planetary objects move in clockwise turns within one track
• The combination of motion could form regular geometrical models of irregular planetary behavior
• Discovering order from disorder motion of the planets is "saving the appearances"

Challenge of Saving Appearances

• Plato cited major observations regarding the movement of stars and planets
• Stars seem to rotate around Earth in a 'perfect' path
• 'Wandering stars' travel the sky with irregular motion patterns throughout the year
• Plato coined the " wandering stars" as planets
• Planets move in a uniform and organized manner orbiting Earth in combination of circles
• The great challenge is explaining ‘wandering stars' that contradict theory of planetary motion
• The great challenge also involves apparent motion of the planets

Principles of Greek Philosophers of Motion

• Widely accepted principles involve the motion of stars, Sun, and planetary objects
• Principles incorporate theory of planetary motion and apparent motion of the planets
• Planetary motion assumes planets moved “perfectly” in a circular motion
• Apparent motions of the planets were based uniformity as moved in their orbits
• Plato was an ancient Greek philosopher and famous student of Socrates, teacher of Aristotle
• Discovering order from disorder motion of planets is “saving the appearances”

True or False Questions - Planets and Motion

• Theory of planetary motion assumed planets moved “perfectly” in a circular motion - TRUE
• Socrates was an ancient Greek philosopher and famous student of Plato who served as the teacher of Aristotle - FALSE
• Idea of discovering order from disorder motion of planets coined as saving appearances was devised by Aristotle. - FALSE
• Apparent motions of the planets were based on uniformity of behavior as moved in orbits - TRUE
• In Plato's era, it was known that the planets move in an irregular manner - TRUE

Early Views on Matter - Empedocles

• (490 BC - 430 BC) argued all things are made of four elements: fire, air, water, and earth
• Combination and ratio of the four elements dictate the matter's properties
• Stone contains a high amount of earth element
• A rabbit has a high ratio of both water and fire elements

The Existence of Atom - Democritus

• (460-370 BCE) coined the small pieces of matter, atomos, meaning 'indivisible'
• Atoms are eternal and indestructible
• Atomos are specific to the material they constitute
• Atomos of stone differs from the atomos of fur

The Modern Atomic Theory - John Dalton

• (1766-1844) constructed and developed first version of Atomic Theory
• Matter is composed of tiny particles
• All matter composed of atoms
• All atoms of an element are entirely identical
• Atoms are indestructible and unchangeable
• Elements react to form defined ratios

Aristotle's View on Motion

• (384 - 322 BCE) believed there are two forms of motion: natural and violent
• Natural motion occurs where an object moves upward or downward due to the weight
• Heavier things fall faster than lighter things.
• Violent motion is a product of pushing or pulling caused by humans
• Violent motion is caused by something and can be voluntary or involuntary
• Throwing a ball is an example of a violent motion
• Violent motion always requires force for it to occur

Galileo's Law of Motion

• (1564-1642) found all bodies move and accelerate regardless of size and mass
• Development of concept of velocity using inclined planes
• Development of idea of force causes motion of an object
• Being at rest is the natural state of an object
• Inertia the resistance of an object to changes in motion

Newton's Laws of Motion

• (1642 - 1727) defined the relationship between motion and energy
• The principle of acceleration is the change in velocity that was induced by force
• Inertia is the resistance in change of velocity that's linked to object's mass
• Momentum is the quantified motion energy equivalent to the mass multiplied by velocity
• First Law: Objects remain at rest or in uniform motion along a straight line unless acted by an external force
• Second law: Object changes velocity change when subjected to an external force- force = change in momentum per time interval
• Third law: An action has on equal sign an opposite reaction force

Early Observable Nonterrestrial Motion and the Diurnal Motion

• Diurnal motion refers to an apparent movement of stars and other celestial bodies around Earth
• Diurnal motion is caused by Earth's rotation from west to east
• If Earth is not spinning, the stars will not appear to move westward, and no diurnal motion will be observed

Annual Motion

• Refers to the apparent yearly movement of the sun across of stars
• Annual Movement is caused by Earth's revolution around Sun
• Projection pathway of Sun with regards to stars is the ecliptic
• Zodiac of 12 constellations appears as Sun appears through ecliptic

Precession

• Refers to conical motion of Earth's axis as it spins
• Earth's axis shifts very slowly (one cycle every 26,000 years)
• Axial precession is caused by the gravity that changes a planetary object's rotational axis

Greek Philosophers and the Elements

• Empedocles (492 BCE to 432 BCE) introduced theory describing things around us
• He argued that all things made up of four elements: fire, air, water, and earth
• Democritus (460 BCE - 370 BCE) proposed small pieces of matter (atomos, indivisible)
• He explained that atomos are eternal and indestructible

Modern Scientists and the Laws of Motion

• John Dalton developed the first version of the atomic theory
• Aristotle introduced the concept of natural and violent motion during the Greek era
• Galileo was the first person to lay down laws of motion
• Isaac Newton developed the three laws of motion
• Diurnal motion refers to the apparent movement of stars and other celestial bodies around the Earth
• Annual motion refers to the apparent yearly movement of the sun across a background of stars
• Precession refers to the conical motion of Earth's axis as it spins

True or False Questions - Earth and the Universe

• Motion of an object within the earth is called non-terrestrial motion - FALSE
• The ecliptic is the projected pathway of the sun with regards to the stars - TRUE
• An object at rest is in its natural form of motion - TRUE
• Newton's second law of motion says action or force in nature has an equal and opposite reaction - FALSE
• Voluntary motion refers to the ability of humans (as well as animals) to move because they have will or capacity to do so - FALSE

Flat Earth Model

• Belief that the earth is plane or discoidal in form
• Early Egyptian, Mesopotamian, and Homer believed world is a disk in ocean

Israelites vs Flat Earth Model

• Israelites thought the earth is like a disc floating in water with arched bowl separating the earth from heavens
• Sky is a dome with Sun, Moon, and other embedded objects in it

History of Spherical Earth Model

• Pythagoras introduced idea of found model of Earth in the 6th century BC
• Anaxagoras (430 BCE) observed that Earth's circular shadow was reflected on moon during lunar eclipse
• Aristotle listed several arguments for spherical 340 BCE
• Earth was spherical since moon and sun were spherical
• North Star is closer to horizon in places nearer the equator
• Surface curve implied by ships hull disappearing first

Evidence of Spherical Earth

• Eratosthenes attempted to measure the circumference of the earth around 240 BCE
• A vertical object did not cast a shadow- during summer solstice in Syene, which was not case in Alexandria
• Angle of the sun rays was determined by measuring the shadow a cast vertical stick made
• Alexandria sun rays make an angle of 7.2° from the vertical, versus Syene's angle of 0°
• The earth curved and the sun's light rays came parallel
• Circumference of earth computed nearly 250 000 stadia: 46,250 km (1 stadia = 185 m) were figured out

Modern Evidence Supporting Spherical Earth Model

• Spacecraft Photographs: Satellite photos show earth is spherical
• Astronauts in satellites orbiting in low Earth orbit have observed the curvature of the planet firsthand
• Lunar eclipses formed one side of moon, forming a dark circle, and the shape shows spherical shape
• Time differences in world due to time zones
• The roundness of the world explains the phenomenon of time zones and the fact that it is constantly rotating on axis
• Airplanes are now able to travel in straight line without falling edges ( circle of Earth)
• Curvature of Earth on horizon if travel transatlantic is noticeable and demonstrates circular shape

Belief in Flat Earth

• Early Egyptian and Mesopotamian believed that the world is a disk in ocean
• Homer (Greek philosopher, 8th century BC) believed that the surface water surrounds a circular, flat Earth
• Israelites thought earth is a floating disc from heavens.
• The sky is a solid dome with the sun, Moon, and other embedded objects
• Pythagoras introduced round earth theory @ 6th century BC

Notable Scientists and Discoveries vs Earth model

• Aristotle listed several arguments for spherical Earth:
  • Spherical moon and sun
  • Positions of North Star -Disappearing ships over the horizon ( 340 BCE
• Eratosthenes measured the circumference of the Earth
  • 250,000 stadia, around 46,250 km. 1 (stadia = 185 m)