Astronomy Lecture Notes Week 05

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Astronomy Lecture Notes Week 05

  1. Intro

  2. Finish the Moon

    1. Connect the lunar phases to the whole sky map.

    2. During what month would the Full Moon be lowest in the sky at transit for a northern observer?

    3. Describe the apparent motion of the 1st Quarter Moon on Dec 22.

  3. The Apparent Motion of the Planets

    1. Diurnal Apparent Motion

    2. Long-Term Apparent Motion

      1. Construct the summary table on the board.

      2. Emphasize that the planets seem to communicate with the Sun in some manner as evidenced by their apparent motions.

      3. Leave them with the following questions

        1. Why do planets go retrograde?

        2. Why do the inferior planets have a maximum elongation of less than 180?

        3. How do the superior planets know to go retrograde at opposition? Why do they brighten at opposition?

  4. The Interpretation of the Apparent Motions of the Stars, Sun, Moon and Planets

    1. Ancient Aristotelian Interpretation

      1. Where are we in the Universe? What would Aristotle say? Why did he say that?

      2. Where were the planets? (On nested spheres within the Celestial Sphere. See Figure)

      3. Principles of Aristotle

        1. Background:

          1. Aristotle lived from 384–322 BCE

          2. At eighteen, he joined Plato's Academy in Athens and remained there until the age of thirty-seven (c. 347 BCE). He tutored Alexander the Great between 356 and 323 BCE.

          3. He believed all peoples' concepts and all of their knowledge was ultimately based on perception. Aristotle's views on natural sciences represent the groundwork underlying many of his works.

          4. His writings cover many subjects – including physics, biology, zoology, metaphysics, logic, ethics, aesthetics, poetry, theater, music, rhetoric, linguistics, politics and government – and constitute the first comprehensive system of Western philosophy.

          5. Rule of Three’s

        2. The location and motion of the Earth: The Celestial Sphere Modelk

        3. The two types of matter

          1. Terrestrial

          2. Celestial

        4. The order of the planets – how was that determined?

        5. Implications: A perfect versus imperfect world

          1. Government

          2. Economics

          3. Personal relations

          4. Our perception of our place in the Universe influences the way we live our lives.

        6. Ptolemy’s Contribution

          1. Background

            1. Lived 90 to 168 CE

            2. a Greco-Egyptian writer of Alexandria, He lived in the city of Alexandria in the Roman province of Egypt, wrote in Greek, and held Roman citizenship.

            3. Ptolemy was the author of several scientific treatises, three of which were of continuing importance to later Islamic and European science.

              1. the Almagest

              2. the Geography and

              3. the "Four Books" on astrology

          2. Basic Deferent Epicycle System

          3. “Improvements to the basic model

            1. The Eccentric

              1. Times of the Sun above and below the celestial equator.

                1. 2013 Fall Equinox on Sep 22

                2. 2014 Spring Equinox on Mar 20

                3. 2014 Fall Equinox on Sep 22

                4. FE to SE = 179 days

                5. SE to FE = 186 days

                6. What does this mean?

                7. The fix while “maintaining” Aristotelian principles.

            2. The Equant

              1. The motions of the planets are more complex that the Sun’s motion and to model the apparent velocity of the planet around its orbit another geometric device called the equant was used.

              2. See McConnell’s Models of Planetary Motion.

        7. Read from Kuhn pg. 74

    2. The Copernican Revolution

      1. Read Copernicus’ preface to Kuhn pg. 137.

      2. Copernicus’ proposal

        1. The Sun was at the center of the Solar system.

        2. The planets orbited the Sun on circular orbits at constant speeds.

        3. The Earth was one of the planets that orbited the Sun and took 365.24i days to complete one orbit.

        4. The Earth rotated once its axis at a 23½  tilt.

      3. Implications of the Heliocentric Copernican model

        1. Why does the Sun appear to move eastward through the stars?

        2. Why do inferior planets have a maximum elongation?

        3. Why do superior planets only go retrograde at opposition and why do they brighten?

        4. The true orbital periods of the planets.

        5. The relative distances to the planets.

        6. See the Handout.

        7. What will I ask of you on the exam?

          1. Calculate the true orbital period?

          2. Recognize that using configurations at observed dates creates right triangles of the planet, Earth and Sun that then can be analyzed using right triangle geometry to give the length of their sides and thus the distance to the planet.

        8. Problems with Copernicus’ original model:

          1. Large religious objections.


            2. Read Kuhn pg. 193.

          2. It didn’t work well: circles at constant speeds.

            1. Show the Copernican Model Figure and compare it to Ptolemy’s.

          3. No proof the Earth moved

          4. No way to explain why the planets orbited the Sun. Gravity did not exist.

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