Lecture 3: The Science of Astronomy: The Basics of Astronomy

1. Lecture 3 (Rebecca-Steve version): Plus Lecture 2: Section 2.4
   1. Welcome: But I'm still not Prof. Rebecca Martin. I just have her slides which are the same as those of Prof. Stephen Lepp---who I also am not. I'm Prof. David Jeffery. Just call me David---one, two, three, "David". I'll be substituting for Prof. Lepp who is unavailable this week for lectures---but he's still running the course via Canvas.
   3. Planets known in ancient times: i.e., the historical planets which included the Sun and Moon, but NOT the Earth which was definitely NOT a planet.
   4. What was once so mysterious about planetary motion?
      1. They move relative to the celestial sphere traveling eastward near the ecliptic.
      2. But sometimes they go westward in apparent retrograde motion.
   5. We see apparent retrograde motion when we pass a planet in its orbit---or in the case of Venus and Mercury, they pass us.
   9. Why did the ancient Greek astronomers reject the real explanation of planetary motion?
      1. File: Star file: parallax_stellar.html.
   10. The ancient Greek astronomers knew that the lack of observable stellar parallax meant the Earth was unmoving relative to the stars were extremely far away---beyond what they thought likely.
       1. But why did they not think the planets orbited the Sun and the Sun orbited the unmoving Earth? They could not measure distances to the historical planets, except they did eventually get a good distance to the Moon of ∼ 60 Earth equatorial radii (R_eq_⊕ = 6378.1370 km)). Their geometry was strong, their instruments were weak.
   11. Stellar parallax is:
   12. Stellar parallax is: Answer.
   13. Section 2.4 Summary:
       1. Actually, lack of stellar parallax was not the main reason, the ancient Greek astronomers thought the Earth was unmoving. Like almost everyone before modern times, the main reason was because the Earth seemed unmoving and also seemed to be the center of celestial axis around which stars and historical planets moved but complications: the historical planets moving on ecliptic relative to the stars with, in the case, of the actual planets apparent retrograde motion.
   14. The ancient roots of science.
   15. In what ways to all humans use scientific thinking.
       1. Yours truly thinks the trial-and-error method (which all people use) and scientific method are distinct though without a hard line between them. The scientific method aims at general understanding through theories, NOT just specific recipes.
       2. Aside from quibbling, astronomy is the oldest exact empirical science, and so the prototype exact empirical science.
   16. Scientific thinking is:
   17. Scientific thinking is: Answer. Yours truly would add that the understanding is via theories which have a range of statuses.
   18. How is modern science rooted in ancient astronomy? Part I. A very early example at a low level. of using the lunar phases---though it's more than Yours truly has ever noticed.
   19. How is modern science rooted in ancient astronomy? Part II. There is a rather complex story to how the days of the week got their names which is rooted in astrology. See homework 4: Question 14.
   20. How is modern science rooted in ancient astronomy? Part III. An obelisk can act as a crude gnomon.
   21. How is modern science rooted in ancient astronomy? Part IV.
       1. See files in /astro/stonehenge.
       2. File: Stonehenge file: stonehenge_videos.html.
   22. Section 3.1 Summary
   23. Section 3.2: ancient Greek science/nature-knowledge.
   24. Why does modern science trace its roots to the Greeks?
       1. One of the cultures that invented philosophy and arguably did the most in natural philosophy. The philosophers did dispense with mythological thinking, though much of their thinking could be considered rational myth.
       2. Did scientific modeling.
       3. Made some progress in mathematical physics.
       4. Did a fair bit of descriptive biology, particularly by Aristotle (384--322 BCE) and Theophrastus c.371--c.287 BCE).
       5. Did a lot of Presocratic philosophers did a lot of fruitful speculative theorizing.
       6. Lots more, but you shouldn't overestimate them either.
   25. Ancient Greek astronomers actually had many difficulties in planetary theory, apparent retrograde motion among them.
   26. The ancient Greek astronomers eventually settled on epicycle models which maintained geocentrism approximately and the Earth at rest approximately at the center of the celestial sphere of the stars (a real celestial sphere on which the stars were at rest. There was a spherical Earth---that part was right. The final stage of epicycle models in ancient Greek astronomy was the Ptolemaic system of Ptolemy (c.100--c.170 CE) presented in his Almagest (c.150 CE) as we call it.
   27. The Ptolemaic system:
       1. File: Ptolemy file: ptolemy_epicycle_equant_animation.html.
       2. File: Ptolemy file: ptolemy_system.html.
   28. How did the ancient Greek astronomers explain planetary motion.
       1. The the Earth at rest approximately at the center of the celestial sphere of the stars (a real celestial sphere on which the stars were at rest.
       2. The motions of planets were made of compounded uniform circular motions. Actually, Ptolemy (c.100--c.170 CE) violated this theory with his equant which he left unjustified theoretically---the crime of Ptolemy.
       3. The heavens were perfect unchanging clockwork as indeed they seemed to observations then existing, except for a few anomalies.
   29. How did Aristotelian cosmology differ from the Ptolemaic system?
       1. See the cartoon of Aristotelian cosmology in aristotle_cosmos.html. Aristotelian cosmology hypothesized by Aristotle (384--322 BCE) ∼ 500 years before the Ptolemaic system---but in the telescoping of history, they seem virtually coeval.
   30. How did Aristotelian cosmology differ from the Ptolemaic system? The answer and elaboration.
       1. Aristotelian cosmology as the historical planets carried by compounded invisible spheres. See File: Aristotle file: aristotle_cosmos.html. The Ptolemaic system had epicycle models. Very different geocentric models.
       2. Aristotelian cosmology was useless for making astronomical predictions. Aristotelians maintained it was approximately physically correct, but nature was too complex to use it as a calculation tool. The Ptolemaic system could be used to make predictions of astronomical events to reasonable ancient accuracy.
       3. Aristotelian cosmology became a philosophical dogma among people interested in theoretical astronomy---very few--- in western Eurasia until circa 1600. The Ptolemaic system (known only in western Eurasia, but as far east as India) was regarded by many as just a calculational tool---and they were right.
   31. Thought question:
   32. Thought question: Answer, but its wrong. Aristotelian cosmology was useless, but the Ptolemaic system could be used to make predictions of astronomical events to reasonable ancient accuracy.
   33. Section 3.2 Summary.
   34. Section 3.3 The Copernican Revolution of the 16th century and 17th century.
   35. How did Nicolaus Copernicus (1473--1543), Tycho Brahe (1546--1601), and Johannes Kepler (1571--1630) challenge geocentric solar system models of Aristotelian cosmology and the Ptolemaic system?
       1. Actually, one figure shows you why Nicolaus Copernicus (1473--1543) proposed heliocentrism (i.e., the heliocentric solar system): File: Copernicus file: venus_elongation.html.
       2. Heliocentrism was a radical idea.
       3. The Earth moved and we didn't notice: it rotated on its axis daily and revolved around the Sun. In fact, it was a planet.
       4. The stars were very far away because they showed no stellar parallax and could be other suns spread through quasi-infinite space.
       5. The physics to understand heliocentrism would not fully exist before the discovery of Newtonian physics by Isaac Newton (1643--1727).
   36. Tycho Brahe (1546--1601).
       1. The Tychonic system.
   37. Johannes Kepler (1571--1630) and Kepler's 3 laws of planetary motion.
   38. ellipse I.
   39. ellipse II.
   40. Which of the following parts of an ellipse is a measure of its shape?
   41. Which of ...? Answer.
   42. Kepler's 1st law.
   43. Kepler's 2nd law of planetary motion.
   44. Kepler's 3rd law of planetary motion.
   45. Kepler's 3rd law of planetary motion: plot I.
   46. Kepler's 3rd law of planetary motion: plot II.
   47. Thought Question:
   48. Thought Question: Answer.
   49. Thought Question:
   50. Thought Question: Answer.
   51. How did Galileo (1564--1642) solidify the Copernican Revolution?
   52. Newton's 1st law of motion, but only sort. Galileo did not have a perfect understanding of it nor of force.
   53. Galileo's early telescopic observations proved Aristotelian cosmology and the Ptolemaic system were both plain wrong. And many people did accept those proofs since anyone could verify them with a telescope. But some did not accept them anyway.
   54. Galileo's discovery of jillions of stars. This does not prove the stars were far away, just that most were dim. But that they were far away and spread through quasi-infinite space seemed very plausible.
   55. The Galilean moons of Jupiter certainly orbit Jupiter, not the Earth was not the center of all Solar System and could still have a moon of its own anyway.
   56. The phases of Venus showed Venus orbited the Sun. So Aristotelian cosmology and the Ptolemaic system were both plain wrong.
   57. The Galileo affair as we call it. The impersonal and personal aspects.
   58. Section 3.3 Summary.
   59. Section 3.4 The Nature of Science.
   60. The scientific method and falsification idealized.
   61. How can we distinguish science from non-science?
   62. Hallmark 3: A scientific theory should make testable predictions at least in principle, but it can make lots of ones that are untestable in direct sense, but they are indirectly testable if not dispensable by Occam's razor and so intrinsic to all testable predictions. The predictions can be of observations you already know, of course.
   63. What is a scientific theory? Really the points cited are for an important, general, still-viable scientific theory. There are lots of disproven scientific theories and some of them were great scientific theories that just turned out to be wrong: e.g., the steady state universe.
   64. Question: A scientific model:
   65. Question: Answer.
   66. Thought question:
   67. Thought question: Answer. Yours truly thinks D is true too aside from pure philosophical skepticism and as a mechanism it is mathematically absolutely true as proven by the genetic algorithm.
   68. Section 3.4 Summary.

2. Lecture 3a (Daniel version):
   1. For the mirror site, IAL: Mirror Site when it needs to exist.
   2. Welcome: But I'm still not Prof. Proga. I just have his slides. I'm Prof. David Jeffery. Just call me David---one, two, three, "David". I'll be substituting for Prof. Proga who is unavailable this week for lectures---but he's still running the course via Canvas.
   4. Scientific thinking:
      1. One basis is trial-and-error method which everyone has always practiced since forever. trial-and-error alone gives you knowledge of a systems, NOT broad general knowledge.
      2. But another ingredient is scientific method in which theorizing and experimentation are done is a cycle in idealized sense.
      3. A theory gives you very general knowledge insofar as it is true.
      4. See sci_method.html.
   5. How was ancient astronomy (the study of which is archaeoastronomy) of use to ancient societies:
      1. Modestly calendrical reasons: the motion of the Sun on the celestial sphere and the phases of the Moon sufficed for ordinary daily life.
      2. Observances sometimes required more elaborate ephemerides like the the computus.
      3. Divination and eventually in some societies astrology.
      4. Very modestly in navigation. They weren't using sextant, nautical charts. and sky maps (AKA star charts). They new certain constellations (NOT our modern IAU 88 constellations) were in certain parts of the sky at given times of the solar year = 365.2421897 days (J2000).
   6. Wikipedia: Lunar phase: Orientation by latitude.
   7. The week Wikipedia: Names of the days of the week. The classical planets take over the rulership of the hours in the sequence Saturn ♄, Jupiter ♃, Mars ♂, the Sun ☉, Venus ♀, Mercury ☿ Moon ☽. See also Wikipedia: Planetary hours: Table of hours, Wikipedia: Planetary hours: History, Vettius Valens (120--c.175 CE) who seems to be the in recorded history to discuss the planetary hours and their rulership.
   8. The ancient Babylonian astronomers eventually were able to predict eclipse phenomena using the Saros cycle and it lasts approximately 6585.3213 days (see Wikipedia: Saros cycle) or 18 Julian years (a Julian year = 365.25 days exactly = 3.1557600*10**7 s ≅ π*10**7 s (underestimate by -0.4489 ... %)), and 10.8213 days (i.e., standard metric day = 24 h = 86400 s).
   9. See sundial London sundial, gnomon (i.e., blade), and obelisk.
   10. See Stonehenge: The Prime Astronomical Monument.
   17. Machu Picchu Wikipedia: Machu Picchu: Intihuatana stone Intihuatana, Urubamba. A somewhat complicated record of Sun ☉ lore.
   18. Wikipedia: Polynesian navigation which included some celestial navigation.
   20. Wikipedia: List of supernovae. The 14th century BCE possible supernova is NOT in the list.
   20. The astronomical monuments mostly recorded astronomy lore. However, El Caracol, Chichen Itza may been an observatory. See El Caracol, Chichen Itza in Yucatan.
   23. See Wikipedia: Ancient Greek science
   26. Aristotelian cosmology (c. 350 BCE) (philosophical truth?) and the Ptolemaic system (c.150 CE) (just a calculational tool or more?) had a long vogue in Western Eurasia till circa 17th century. No one in the rest of the world had heard of them, of course.
   27. Eratosthenes (c.276--c.195 BCE) and Parmenides of Elea (early 5th century BCE).
   29. apparent retrograde motion
   30. Ptolemy (c.100--c.170 CE) Ptolemaic system (c.150 CE).
   34. The migration of Greek scholars in the Renaissance after the Fall of Constantinople (1453) only aided some aspects of the Renaissance which was had already been in progress since c.1400 in some opinion (see Wikipedia: Renaissance: Origins). Renaissance astronomy may have been helped a bit.

3. Lecture 3b (Daniel version):
   1. For the mirror site, IAL: Mirror Site when it needs to exist.
   2. Welcome: But I'm still not Prof. Proga. I just have his slides. I'm Prof. David Jeffery. Just call me David---one, two, three, "David". I'll be substituting for Prof. Proga who is unavailable this week for lectures---but he's still running the course via Canvas.
   3. Nicolaus Copernicus (1473--1543) and the Copernican Revolution:
      1. copernicus_portrait.html.
      2. Copernicus still used epicycle model like Ptolemy (c.100--c.170 CE). He had to in order to make the Copernican system predictive. His contemporary Renaissance astronomers needed that in order to take the Copernican system seriously---which, in fact, they did as tour de force of mathematical astronomy though NOT of physical reality.
      3. ptolemy_epicycle_equant_animation.html.
      4. But why did Nicolaus Copernicus (1473--1543) do it? See venus_elongation.html.
      5. copernican_cosmos_digges.html.
   4. Tycho Brahe (1546--1601):
      1. tychonic_system.html: Up-to-date, but NOT too radical. It was the Copernican system turned on its head. all the geometry was the same, but Earth was at rest.
   5. Johannes Kepler (1571--1630):
   11. Kepler's 3rd law: It connected orbital geometry and kinematics and this begged for a new dynamics to show why. The new dynamics turned out to be Newtonian physics.
   16. Galileo Galilei (1564--1642) and the 3 overcoming of objections:
       1. Only for those who accepted Galilean physics which was NOT as complete Newtonian physics, and so was NOT as convincing.
       2. The Heavens were NOT perfect and therefore did NOT have to have "perfect" circular orbits. However, Galileo himself NEVER considered non-circular orbits. He NEVER assimilated the work of Johannes Kepler (1571--1630). Fact is, he just was NOT in Kepler's league as a mathematician.
       3. I do NOT think Galileo overcame this objection in an empirical sense. stellar parallax was NOT observationally detected until 1838 by Friedrich Bessel (1784--1846) (see Wikipedia: Stellar parallax: 19th and 20th centuries; Wikipedia: Friedrich Bessel: Work). Galileo's work probably did make it seem a less important objection and by circa 1700 most astronomers probably did NOT think it an important objection at all.
   19. I think this is a bit of a fine point of argument. Galileo showed that stars stayed point-like in the telescope which meant they were much farther than planets OR much smaller. The former is true, but Galileo could NOT prove that. Of course, if you believed the stars were other Suns then they were far away and the lack of OBSERVABLE stellar parallax was NOT an objection to heliocentrism.
   20. The discovery of the Galilean moons of Jupiter ♃:
       1. Proved Aristotelian cosmology and the Ptolemaic system did NOT know everything about the cosmos since they did NOT know about the Galilean moons.
       2. Proved the Earth was NOT unique center of motion as in Aristotelian cosmology and the Ptolemaic system, and so they were WRONG about that.
       3. It suggested (but did NOT prove) that smaller astro-bodies had to orbit larger astro-bodies relative to the fixed stars. If so, the Earth had to orbit Sun and NOT vice versa relative to the fixed stars as SEEN from another astro-body moving slowly relative to the fixed stars like like Jupiter ♃ itself or a fixed stars. Recall, from the Earth's perspective, the Sun does geometrically orbit the Earth. But we consider this a geometrical orbit since it is NOT relative to the center of mass of the Solar System in Newtonian physics. But this perspective was NOT available to Galileo's contemporaries, and so how exactly to decide the argument then was NOT clear I think. If you were already a convinced heliocentrist, then you already had a consistent theory of what orbits what in a physical or causal sense.
   21. The phases of Venus proved Aristotelian cosmology and the Ptolemaic system were just plain WRONG. Venus in a direct sense orbited the Sun. But this was consistent with the Tychonic system as well as heliocentrism.
   22. So much is known of the Galileo affair that I won't say much about it. In fact, UNLV has a great expert on it, Maurice A. Finocchiaro, UNLV Distinguished Professor Emeritus who has written The Galileo Affair 1989.
   24. This has to be qualified. The work of Galileo, Johannes Kepler (1571--1630), and others EVENTUALLY made heliocentrism the most plausible theory of the Solar System to most of those interested in astronomy. To prove heliocentrism in the context of a physical theory, it had to be proven by that physical theory. This proof was given Isaac Newton (1643--1727) in his book Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy") (1687) which presented what we call Newtonian physics. However, Newton probably believed heliocentrism ever since he learned anything about astronomy since all of his teachers did. Newton would have been surprised if heliocentrism had turned out to be WRONG.
   27. The scientific method.
   31. These statements are in the realm of philosophy of science and NOT everyone would agree with them or would agree only with qualifications:
       1. For example, yours truly believes some theories are so well established that they are correct/true within the range of validity aside from pure philosophical skepticism, Newtonian physics for example.
       2. Occam's razor is a useful rule, but you have to make a judgment about "simpler" and different some people might make different judgments. Also some might say, particularly about profound theories, that "simpler" is NOT the right comparison tool. For example, consider the comparison between the Aristotelian cosmology, the Ptolemaic system, the Copernican system, and the Tychonic system. There were so many dimensions to the comparison in circa 1600 that it was hard to say which was "simpler" or whether "simplicity" was the right comparison tool. Or for another example, in most respects people would say Newtonian physics is simpler than the theory of relativity (meaning both special and generality), but even before any there was any ordinary evidence preferring theory of relativity, a very insightful person might say the theory of relativity is to be preferred since it answers questions which have NO answers in Newtonian physics.
   32. Most people would agree with this statement, but with qualifications. One is that observations/experiments can be faulty. In some cases, it takes a long time for a theory to be proven wrong. There are other objections too.
   34. A key objection by yours truly. A scientific theory is still a scientific theory if it has been proven wrong: it's then a wrong scientific theory. Actually, wrong scientific theories can be brilliant and educationally useful, and they might later prove to right with some changes.
   35. Yours truly agrees with (c), but in a nuanced sense yours truly believes (d) too.
   36. Again scientific theories are still scientific theories even if they are wrong.
   37. Astrology.
   38. Horoscopes:
       1. Johannes Kepler (1571--1630).
       2. brutus_james_mason.html.
   43. Galileo dispelled, but not totally dispelled.
   45. Some people in the 16th century did hope the Copernican system would make better predictions.