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99 years modern astronomy

Jul 12, 2015



  • 16 CENTURIES From the time of Claudius Ptolemy to the time of Nicolaus Copernicus, it was the Ptolemaic model that was accepted.

  • Thales (625 - 546 BC) - prediction of the eclipse of the sun in May 28 585 BC.

    Pythagoras (582 - 500 BC) - considered the Earth as a globe revolving with the other planets

    Anaxagoras (500 - 428 BC) - explained eclipses and believed the moon was part of Earth

  • Eudoxus (408 - 355 BC) - first to explain the movement of planets

    Heraclides (387 - 312 BC) - proposed the sun is the center of the solar system;observed Mercury and Venus

    Pytheas (380 - 300 BC) - observed the Pole Star is not the true pole and that the moon affects the tides

  • Pre-Copernican Astronomy The Golden Age of Astronomy

  • Nicolaus Copernicus

  • Nicolaus Copernicus (1473 - 1543)Polish Canon

    De Revolutionibus Coelestium Orbium

    Heliocentric Model

    Father of Modern Astronomy

  • The Copernican SystemPlaced the Sun at the center

    His theory did not predict planetary positions accurately

    Retained epicycles and deferents

    The Copernican theory was wrong but the Heliocentric idea was right.

  • Tycho Brahe (1546-1601)Called Tycho, the man with the golden nose.

    Studied for law but went to astronomy and mathematics

    The Observational Astronomer

  • Tychos WorkFound errors in the astronomical tables of the times

    Studied the motion of planets

    in 1572, observed the supernova (Tychos supernova)

    Carefully gathered data about planetary positions

  • Tychos TheoryBelieved earth was stationary

    Rejected the Ptolemaic theory because of its wrong predictions of positions of heavenly bodies

    Made the earth the immobile center of the universe

    Devised new and better instruments

    Hired an assistant, Johannes Kepler

  • Tychonian ModelEarth is the immobile center

    The moon orbits around earth.

    The sun orbits the Earth!

    Planets orbit around the sun.

  • Johannes Kepler

  • Johannes Kepler (1571-1630)Three Laws of Planetary Motion

    His Book: Harmonice Mundi (The Harmony of the World)

  • Keplers TheoryAbandoned CIRCULAR MOTION

    Instead, he discovered the ELLIPSE as the orbit of Mars

    Discovered that planets do not move at constant speed

    In his book, he came within a paragraph of discovering the law of mutual gravitation.

    Laws of Planetary Motion

  • The Three Laws of Planetary Motion1st Law: Law of EllipsesAll planets revolve around the Sun in orbits that are ellipses, and the sun is located at one of the foci.2nd Law: Law of Equal AreasA line drawn from the planet to the sun sweeps out over equal areas in equal intervals of time.3rd Law: Law of HarmonyThe square of the period (in earth years) of a planet is equal to the cube of its average distance (in astronomical units) to the sun.T 2 r 3

  • By now, it is clear the planets revolve around the sun and the orbits are not circles but ellipses. The next question is:

    What keeps the planets moving around the sun?

  • Galileo Galilei

  • Galileo Galilei (1564 1642)Defender of Copernicanism

    Made important discoveries about motion.

    Defended the theory that the Earth moves.

    Earth moves.

  • Galileo GalileiMade telescopes & used it for astronomy

    Discovered the moons of Jupiter, the phases of Venus and the sunspots

    Taught that the Earth moves

    Fell into controversy with the church authorities

    Believed that the Earth is not the center.

  • Question:If planets move, what or who keeps them moving?

    Principle in those days: Quidquid movet, ab alio movetur.Whatever is moving, is moved by another? So what moves the planets?

  • Galileos Answer:There is no need for a mover. The planets go on by themselves. Galileo studied motion and found that once a body is in motion, it will tend to continue in that state of motion. Nothing!(Yeah it sounds like Newton, who later borrowed it and made it his first law.)

  • Galileo had explainedwhat moves planets (the red line) is inertia. The remaining question is what keeps them in orbit? Gravitation, which brings us to Newton.

  • Isaac Newton

  • Isaac Newton (1642 - 1727)His great work: Principia Mathematica Philosophiae Naturalis Mathematical Principles of Natural Philosophy

    Law of Gravitation

  • The Principia

  • For Isaac Newton there is only one remaining question

  • If planets tend to go on along straight lines, why do they not fly off into space?

  • Newtons SolutionAny mass (object) exerts a force called gravitation.

    Gravitation is the property of a mass to pull other masses to itself.

    Between a chair and table, between an apple and the earth, between the sun and the planet there is attraction.

  • Inertia makes a planet move along a straight line but at the same time, there is a pull exerted by the Sun on a planet. The result is that the planet does not fly to space nor does it fall to the sun. The combined motion becomes the elliptical orbit around the Sun.

  • Two motions happen at the same time.

    The planet tends to fly off.

    Gravitational force pulls the planet to the center.

    Result: the orbital motion

  • In these 99 years (1543-1642), it has been established:That the sun is the center of the solar system

    That the Earth moves.

    That planets move in elliptical paths.

    That the orbits are maintained by inertia and gravitation.

  • Write TRUE if the statement is correct and if False, WRITE the word/s that makes the statement incorrect and opposite to it is the correct answer.Ex if false: Blue -> Red

    1. Johannes Kepler believed that the earth is the immobile center.2. Copernicus heliocentric idea was correct and predicted the planetary positions accurately.3. Kepler improved the telescope that brings the discovery of the different phases of the Venus.4. Tycho hired Kepler as an assistant.5. Isaac Newton gives the Law of Planetary Motion.6. Galileo defend Copernicus heliocentric idea.7. Eratosthenes was famous for his measuring earths diameter.8. Hipparchus invented the armillary sphere.9. Ptolemy proposed the spherical universe.10. Aristarchus was the first to push the idea of heliocentric system.