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  • PHYSCI: How Did The Ancient Greeks Prove That The Earth Wasn't Flat?

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    Alyanna Lumanglas
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    1) Around 500 BC, the ancient Greek philosopher Pythagoras first proposed that the Earth was round rather than flat based on observations of lunar eclipses showing the Earth's shadow was circular. 2) Later Greek astronomers made additional observations supporting a spherical Earth like ships disappearing over the horizon and stars appearing higher in the sky in Egypt. 3) In the 16th century, Nicolaus Copernicus proposed a heliocentric model where the Sun is at the center, marking a shift from the geocentric Ptolemaic system of circular orbits around a stationary Earth.

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    PHYSCI: How did the Ancient Greeks Prove that the Earth Wasn't Flat?

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    1) Around 500 BC, the ancient Greek philosopher Pythagoras first proposed that the Earth was round rather than flat based on observations of lunar eclipses showing the Earth's shadow was circular. 2) Later Greek astronomers made additional observations supporting a spherical Earth like ships disappearing over the horizon and stars appearing higher in the sky in Egypt. 3) In the 16th century, Nicolaus Copernicus proposed a heliocentric model where the Sun is at the center, marking a shift from the geocentric Ptolemaic system of circular orbits around a stationary Earth.

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    1K views2 pages

    PHYSCI: How Did The Ancient Greeks Prove That The Earth Wasn't Flat?

    Uploaded by

    Alyanna Lumanglas
    1) Around 500 BC, the ancient Greek philosopher Pythagoras first proposed that the Earth was round rather than flat based on observations of lunar eclipses showing the Earth's shadow was circular. 2) Later Greek astronomers made additional observations supporting a spherical Earth like ships disappearing over the horizon and stars appearing higher in the sky in Egypt. 3) In the 16th century, Nicolaus Copernicus proposed a heliocentric model where the Sun is at the center, marking a shift from the geocentric Ptolemaic system of circular orbits around a stationary Earth.

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    of 2

    LESSON 1.

    1 Ancient Greek Astronomy and


    Lesson 1.1 Cosmology: How did the Ancient Greeks Prove that
    the Earth Wasn't Flat?

    Ancient Greek
    Around 500 B.C., most
    Astronomy and Greeks believed
    Cosmology that the Earth was round,
    not flat. It
    How did the was Pythagoras and his
    Ancient Greeks pupils who
    Around 500 B.C., most
    Prove that the Greeks believed that
    Earth Wasn't the Earth was round, not
    flat. It was
    Pythagoras and his
    EXPLORE! pupils who were first to
    Lesson 1.1 Around 500 B.C., most Greeks believed that the Earth was round,
    not flat. It was Pythagoras and his pupils who were first to propose

    Ancient Greek
    a spherical Earth.

    In 500 to 430 B.C., Anaxagoras further supported Pythagoras’


    proposal through his observations of the shadows that the earth cast

    Astronomy and on the Moon during a lunar eclipse. He observed that during a
    lunar eclipse, the Earth’s shadow was reflected on the Moon’s
    surface. The shadow reflected was circular.

    Cosmology Key Observations that led the Greeks to conclude that the Earth is
    spherical:

    How did the  The Shadow that the Earth casts on the Moon during a
    lunar eclipse is circular.

    Ancient Greeks
    Polaris - North Star was believed to be at a fixed position in
    the sky. However, when the Greeks traveled to places nearer
    the equator, like Egypt, they noticed that the North Star is
    closer to the horizon.

    Prove that the  The Shape of the Sun and the Moon - Aristotle argued that if
    the Moon and the Sun were both spherical, then perhaps, the
    Earth was also spherical.

    Earth Wasn't  Disappearing Ships - If the Earth was flat, then a ship
    traveling away from an observer should become smaller and
    smaller until it disappeared. However, the Greeks observed

    Lesson 1.1 that the ship became smaller and then its hull disappeared first
    before the sail as if it was being enveloped by the water until
    it completely disappeared

    Ancient Greek  The Size of the Spherical Earth - Ancient scholars tried to
    provide proof of a spherical Earth and its circumference
    through calculations. It was Eratosthenes who gave the most

    Astronomy and accurate size during their time.

    Geocentric vs. Heliocentric Model of the Universe


    Cosmology Assumed all heavenly bodies to be spherical in shape.
    GEOCENTRIC MODELS OF THE UNIVERSE the motion of the object observed, or of the observer, or
    - Earth is the center of the universe indeed to an unequal change of both."
    - He proposed a heliocentric universe of the cosmos: in this
    PYTHAGOREAN MODEL model, the earth rotates on its axis once every twenty-four
    - Earth is round - heavenly bodies move in circle hours, and the Earth revolves around the sun once every
    ”THE MUSIC OF SPHERES” MOTION OF PLANETS year.
    WERE MATHEMATICALLY RELATED TO MUSICAL - In his heliocentric model, retrograde motion disappeared.
    - “the music of spheres” motion of planets were Retrograde motion of the planets is explained by the Earth's
    mathematically related to musical sounds and numbers motion, which in short was also influenced by planets and
     Plato’s "saving the appearances" other celestial bodies around Earth.
    - Plato adopted the Pythagorean model and described the - He dictated a definite order of the planets: Mercury, Venus,
    motion of all heavenly bodies to be are perfectly circular, Earth, Mars, Jupiter, and then Saturn.
    ethereal/perfect - Copernicus’s theory also made the universe twenty times
    - However, Plato’s students could see that Mars seems to be wider across than Ptolemy. Explaining the distance from the
    jumping backwards, showing retrograde motion. (movement Earth to the Sun is small compared to the distance to the stars.
    of planets from WEST to EAST).
    - He used Plato's 4 element theory plus the idea of The Problem with Copernicus' Mode
    "ether"(earth, water, air, fire). - Considered by most people to be wrong, and many found the
    - He assumed that the earth was the center of the universe since idea downright blasphemous.
    it is the heaviest element, water was lighter than the earth so - It was also very inconsistent with Aristotelian mechanics.
    the oceans rested on top of the earth. Air’s natural state is - He banked on Ptolemy's fifteen-hundred-year-old data to build
    above water and fire sat on top of air. his system.
    - Beyond these four terrestrial spheres—out past the Moon— - Copernicus's math was a disaster
    spun the stars.
    - Believed that all stars are fixed points which rotate on a single
    celestial sphere. It has 56 spheres
    - Prime mover- drives the motion of the planets

    EUDOXUS’ MODEL
    - The Sun, planets, and stars were then placed in giant
    transparent spheres surrounding it. 

    HOMOCENTRIC MODEL
    - Celestial spheres share one common center-earth
    - 1st model of geocentric model
    - Made up of 27 spheres
    - 5 planets

    PTOLEMY’S MODEL
    - The Earth is at the center of the universe. The stars are fixed
    on a sphere that revolves around the Earth, and the planets
    (and the sun) revolve around the Earth at different distances.
    Everything moves on perfect circles with constant speed.
    - To account for Mars' retrograde motion two ingenious
    geometrical devices were invented: the deferent (circular
    path in which planets move) and the epicycle (a point close
    to the orbit’s center).
    - Planets move at a constant speed on the epicycle, and the
    epicycle moves at a constant speed on the deferent around
    the Earth. The combination of the two motions results in the
    planet executing retrograde motion, with respect to the fixed
    stars.
    - Proposed the equant (a point close to the orbit’s center)

    HELIOCENTRIC MODELS OF THE UNIVERSE


    - The Sun is the Center of Universe.

    ARISTARCHUS’ MODEL
    - Ancient Greek, Aristarchus was the first man who place the
    sun at the center of the universe
    - The sun and the stars are fixed
    - The earth is revolving around the sun in a circular orbit
    NICOLAUS COPERNICUS
    - Copernicus realized that an object moving around you from
    left to right looks the same as an object standing still while
    you rotate from right to left.
    - In his book, On the Revolution of Heavenly Spheres, he
    wrote: "Every apparent change in respect to position is due to

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