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SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond

SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond. Lecture 2 29 January 2014 Science Center Lecture Hall A. Outline of Lecture 2. “Housekeeping” Objects in sky

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SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond

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  1. SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond Lecture 2 29 January 2014 Science Center Lecture Hall A

  2. Outline of Lecture 2 “Housekeeping” Objects in sky Patterns of motions of objects Observations Effects of patterns on humans Models

  3. “Housekeeping” Final Exam: 13 May Asking questions in lecture: encouraged!

  4. Objects In Sky Sun (one) Moon (one) Stars (semi infinite) Planets (five)

  5. Patterns Of Motions Of Objects Sun: Circles earth rapidly in day, noon to noon Circles sky more slowly in year, spring equinox to spring equinox Subtleties: different lengths of days different lengths of seasons different measures of year (solar, above, and sidereal, with respect to stars; see next slide) Total (and partial) eclipses

  6. Sidereal (Star) Day Vs.Solar Day

  7. Patterns Of Motions Of Objects(cont’d) Moon: Phases Variable lengths of months Longer-period variations (e.g., 19 year metonic cycle: 235 months ≈ 19 years) Eclipses (shows earth is round)

  8. Patterns Of Motions Of Objects(cont’d) Stars: Rigid daily circling of sky Point in sky about which circling happens moves about 1.4 degper century (“precession”): North Pole moves on sky

  9. Patterns Of Motions Of Objects(concluded) Planets (“wanderers”): Don’t twinkle in contrast with stars Orbits all in nearly same plane Orbital periods all different Retrograde motion (see next slide) a puzzlement

  10. Mars’ Retrograde Motion(Schematic; 35 Day Point Separation)

  11. Observations Naked-eye observations only Observations over long time lines allow high accuracy in orbital period estimates (see next slide and demo) Recordings started by Babylonians in cuneiform (see next slide), going back at least to 700 BCE; brought to Greece probably by Hipparchus (c. 190 – 120 BCE) Chinese recorded solar eclipses earlier

  12. How Accurate Was Knowledge Of Orbital Periods In Ancient Times? Secret: Monitor over long time periods For an orbital period, P, and uncertainty, U, in measuring epochs, error in estimating P will decrease inversely with number, n, of periods observed: P(estimated) = [nP ± U]/n = P ± U/n NB. Analogy with person’s pace; part “gedanken” experiment (see demo)

  13. Cuneiform Tablet

  14. Effect Of Patterns On Humans Science – to what end? Practicality (food: crops and hunting) Religiosity (astrology) Mark important annual dates Curiosity Production of calendars to meet above needs: See next three slides The week (see fourth slide from here)?

  15. Calendar Construction Problem? - Incommensurable numbers (ratios of lengths of year to day and month to day are not integers or simple fractions)

  16. How to Handle? Round to nearest integer, with each of year and month expressed in days Problem: Calendar “drifts” (e.g., in North, winter will eventually arrive in July: 365¼ 365) Solution: Leap concept (long, interesting, many- country history) Current civil calendar: Gregorian (late 16th century, apparently “universal” as of 1 Jan 1927) Practice makes perfect: Homework problem

  17. Calendar Contrasts Gregorian captured civilian world (why?) Some other calendars: Chinese Hebrew (lunar) Hindu Islamic (lunar) Mayan Scottish (oldest known)

  18. From Whence the Week? No astronomical basis. Origin unknown Why 7 days? Hint in names? Maybe English: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday French: Dimanche, Lundi, Mardi, Mercredi, Jeudi, Vendredi, Samedi Why this order? Unclear Not “even” (integer) number of weeks per month or per year. No one seems to care (Divisions of day: non-astronomical)

  19. Models Aristotle (setting the scene: sky and earth) Sun (see next three slides) Moon (same type of model as for sun) Planets (problem and partial solution for retrograde motion; see fourth slide from here)

  20. Sun (Green) Moves Uniformly Around Circle Offset from Earth (Blue)

  21. Hipparchus’ Model Of Sun

  22. Current Lengths Of Seasons Winter: 88.99 days Spring: 92.75 Summer: 93.65 Fall: 89.85 Spread of almost 5 days; different in Hipparchus’ day

  23. Epicycle Yields Retrograde Motion(Deferent Is Large Offset Circle)

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