The History and Nature of Astronomical Discovery - AST 210 H1

Renaissance Astronomy and the Newtonian Revolution

This section of the course is based mainly on material in the first three chapters in the 5th and 6th editions (Prologue and Chapters 1, 2 and 3 of the 4th edition) of the textbook,"In Quest of the Universe". In the outline below, I indicate the material you should read and which of the terms that are highlighted in bold face or italics you should know.

Chapter 1 - An Earth-Centered Universe

  • Introduction
  • The View from Earth> Brief overview.
  • 1-2 (4th ed: 1-1) The celestial sphere: north celestial pole, south celestial pole, celestial equator, the relationship between the Earth's poles and equator to their celestial counterparts, the importance of the star Polaris, angular separation, constellations
  • 1-3 (4th ed: 1-2) The Sun's motion across the sky: ecliptic, zodiac, vernal equinox, autumnal equinox, summer solstice, winter solstice, the Sun and seasons, altitude, leap year and the calendar
  • 1-4 The Moon's phases: Waxing, waning, gibbous, crescent, New, first quarter, full, last quarter. Sidereal and synodic period.
  • 1-5 Lunar Eclipses: umbra, penumbra; eclipse season (inclination of orbits, line of nodes). (diagrams to illustrate a lunar eclipse and photos of the Moon during lunar eclipses are shown in Figs 1-24 to 1-30 (4th ed: page 172-173), Earth.)
  • 1-6 Solar Eclipses: Umbra, penumbra; total, annular, partial eclipses.
  • 1-7 Observations of Planetary Motion: prograde, retrograde motion. Elongation.
  • 1-8 Rotation: solar & sidereal day.
  • 1-9 to 1-11 Units of distance in Astronomy: AU, light year, parsec. scale of Universe
  • LECTURE NOTES are in the Blackboard Course Documents area.

    Chapter 2 - From Earth-Centred to Sun-Centered System. You should read all of this chapter.

  • 2-1; 2-2 (4th ed.:1-3) Scientific models: Criteria for scientific models: Occams's razor, model, theory and hypothesis, astrology and science
  • 2-3 The Greek geocentric model: The evidence that convinced Aristotle and other Greek scientists that Earth is spherical, why Aristotle rejected the idea that the Earth moves, parallax, stellar parallax, Aristotle's system of the world, Ptolemaic model, observations of planetary motion, retrograde motion, epicycles and how they account for retrograde motion, how the epicycles for Mercury and Venus differ from those of the other planets in the Ptolemaic model
  • 2-4 (5th Ed: 2-3; 4th ed:1-5) Aristarchus's heliocentric model: how he determined the relative distance to the Sun, the relative sizes of the Moon/Earth and the relative sizes of the Moon/Sun, how Eratosthenes measured the size of the Earth, zenith, conclusion.
  • 6-1 Measurement of the Moon's Distance and Size: Aristarchus. Small angle formula.
    See also: The Moon's Distance notes by David Stern.
  • 2-5 (4th ed:2-1) The Marriage of Aristotle and Christianity
  • 2-6 (4th ed:2-2) Nicholas Copernicus and the Heliocentric Model: Copernicus and his times, the Copernican system, motions of the planets.
    Note pages 66 - 68 about how Copernicus could obtain the relative sizes of planetary orbits (assuming circular orbits).

  • 2-7 (4th ed: 2-3) Comparing the Two Models: accuracy in fitting the data, parallax, predictive power, astronomical unit, aesthetics: Mercury and Venus, De Revolutionibus
  • 2-8 (4th ed:2-4) Tycho Brahe: The Importance of Accurate Observations: Tycho's model. For an up-to date account of the death of Tycho, the following website should be consulted: How Tycho Brahe Really Died
  • 2-9 (4th ed:2-5) Johannes Kepler and the Laws of Planetary Motion: Kepler's three laws, ellipse, focus of an ellipse, eccentricity of an ellipse, perihelion, aphelion, sidereal period.
    Regarding Table 2-2 (same in 4th & 5th eds.), you should know the names of the eight planets (and "dwarf planet") in our solar system and be able to list them in order of increasing sidereal period and mean distance from the Sun.
    Note: You will not be required to make calculations requiring a calculator (like the one in the example on page 61 [p. 57 in 5th ed.]) on the quizzes or tests, but you do need to understand the concepts and relationships, such as Kepler's Laws, and remember the powers of things; any numerical results can be obtained with mental arithmetic.
  • 2-10 (4th ed:2-6) Kepler's contribution, conclusion.

Chapter 3 - Gravity and the Rise of Modern Astronomy

  • Introduction
  • 3-1 Galileo Galilei and the Telescope: observing the Moon, the Sun and the stars, Jupiter's moons, Galilean moons, Galileo Galilei, the phases of Venus, full, gibbous, crescent, quarter, see also Figure 1-24 to compare with phases of the Moon
  • Interesting background information on Galileo can be found at . (This is for interest and understanding, not extra examinable material!)
  • 3-2 Isaac Newton's Grand Synthesis: Newton's first two laws of motion, inertia, acceleration, force, Isaac Newton, an important digression - mass and weight, back to Newton's second law, Newton's third law, action, reaction
  • 3-3 Motion in a circle: centripetal force
  • 3-4 The Law of Universal Gravitation: weight, arriving at the law of universal gravitation, inverse square law.

  • 3-5 Newton's laws and Kepler's Laws: travel to the Moon, binary systems, Newton's expansion of Kepler's third law (relating mass, semimajor axis, orbital period). Note Figures 3-16 (p.86 in 6th ed.)
  • 3-6 Orbits and the Centre of Mass: centre of mass, barycentre
  • 6-2 (4th Ed.: 3-7) The Tides: differential gravitational pull, spring tides, neap tides, tidal friction.[Discussion in 4th Ed. more complete]
    Rotation and revolution of the Moon; precession of the Earth.

Short Readings from Other Chapters

  • In addition to the readings from chapters 1 to 3, we discuss a few brief sections from subsequent chapters. These illustrate the importance of Newton's law of gravitation and his expansion of Kepler's third law.
  • Cometary orbits - Isaac Newton and Edmund Halley (page 285-286 [334-341 in 5th ed.] in chapter 10). Sections {\bf 10-4 and 10-5 (6th,5th,4th eds.)}: the nature of comets and the Oort and Kuiper clouds. Additional material is given in the lecture notes. See Wikipedia on: Comets, Oort Cloud for interesting information and explanations.
  • William Herschel, Musician/Astronomer: telescope builder, the discovery of the planet Uranus, discovery (with the help of his sister Caroline) of the existence of stars in orbit around one another (binary stars) - pages 267, 354-357 (307 4th ed.) in chapter 9.
  • Further discussion of the discovery of binary stars, in particular, visual binaries - pages 357-353 (379-380 5th ed., 410 and 411 4th ed.) in chapter 12, including Figures 12-23 to 12-25 (Fig. 12-26 in 4th ed.). If the orbital period and the mean separation of the two stars can be derived, the total mass of the system can be calculated from Newton's extension of Kepler's third law (see page 84 [p.87 in 5th ed. ; p.80 in 4th ed.]). If each star's distance from the barycentre can be derived, the individual masses can be calculated (see Example).
  • The Discovery of Neptune - page 271 [5th ed.:p.289; 4th ed.:p.314] in section 9-4.
  • The Mass of the (Milky Way) Galaxy: section 16-2 in chapter 16 (all 3 eds.).
    The point here is to understand how Newton's extension of Kepler's third law can be used to derive the mass (see the discussion on pages 520-522). Even though the period of the revolution of a star around the centre of the Galaxy can not be directly measured, it can be estimated from the star's speed and its distance from the galactic centre. Another point to note is that Figure 16-13b demonstrates that about 90% of the mass of the Galaxy is not visible.
  • The Masses of Galaxies: section 17-3 in chapter 17.
    In this section, you should understand the three methods for determining masses of other galaxies. These are explained on pages 491-493 [5th ed.:556-558] and all of them are based on Newton's extension of Kepler's third law. You should also understand the term, dark matter. All of the methods for deriving galactic masses have demonstrated the presence of dark matter.

  • Lecture Notes 1-8 are posted on Blackboard in PDF .

    Material on the speed of light we will leave to the second Term Test.

    *** (The following item on Neptune is for interest only: There is an interesting addendum to the story as told in your textbook. Some important correspondence was stolen from the Royal Greenwich Observatory in the mid 1960s and was not recovered until the late 1990s. It indicates that perhaps Adams was not as good nor Airy as bad as the "traditional" story indicates. A website at University College London: Neptune's Discovery documents this. There was also an article "The Case of the Pilfered Planet: Did the British steal Neptune?" in the December 2004 issue of Scientific American.
    It turns out that the first person to record a telescopic observation of Neptune was Galileo. In 1613, the planet Jupiter occulted Neptune and Galileo used Neptune as a reference star on two occasions when he was studying the motions of the principal moons of Jupiter.) ***

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