Motions in the Sky

1. Motions in the Sky Watchers and Timekeepers

2. The Milky Way over Utah

3. The First Science • Unless you were a troglodyte* thousands of years ago, you couldn’t help but notice that the sky changed, hour by hour, day by day, month by month, year by year *someone who lives underground

4. The Sun rose and set and sometimes even disappeared; • The Moon also rose and set, changed shape, and occasionally turned red; • There were patterns in the night sky that came into view at different times of the year; • There were stars that defied the patterns and marched recklessly across the sky; • And there were often visitors in the heavens.

5. Astrologers: precursors to Astronomers* • As in any population, there were a few geeks who took great interest in what was happening in the sky • These people never knew the cause of the events and phenomena they observed, but they did keep track of their periodicities • And they were good storytellers! *Discussed in another ppt.

6. Great mysticism was attached to the goings-on in the sky • The people who recognized the repetition of celestial events and could make predictions of the next occurrence were therefore seen as shamans • Shamans in a society wield great power • The ability to predict phenomena in the sky extended back down to Earth and the supposed ability to foresee the future • Often for personal gain

7. Time • Since celestial events happen with a regularity, the shaman astrologers could use this periodicity to construct calendars (coming up in a minute) • Even today our calendars are closely attached to Astronomical phenomena • But it took millennia to iron out all the kinks

8. Months and Years • The most obvious cyclic events in the sky are the rising and setting of the Sun and the Moon • Important to realize is the fact that these rising and settings vary from day to day • Also critical is to understand that the Sun and the Moon cycles are not connected

9. The Sun rises in a different place every day

10. These four special days mark out many calendars

11. They are: Winter Solstice, Vernal Equinox, Summer Solstice, Autumnal Equinox

12. Northern Hemisphericocentric* • The Southern Hemisphere has equivalent days • The Sun’s rising position changes over a year, from south of East in December to directly east in March to north of East in June and back to East in September • And all points in between • Same all year long on the equator *not a real word

13. Effects • This changing rise position is caused by the tilt of the Earth relative to the Sun and by the motion of the Earth around the Sun • The tilt is what causes the Seasons* • Ancient astrologers did not know about the tilt or the orbit, but they knew the cycle repeated after about 365 days *discussed in another ppt

14. Analemma • Not a regular path in the sky • Left: each picture was shot on a different day but at the same time over a year

15. Important Days • The four Astronomically important days delineated the four Seasons, although some cultures like the ancient Egyptians recognized only three • Please realize that ancient peoples did not necessarily have a December, March, etc., but the two solstices and the two equinoxes were recognized nonetheless

16. The Moon • Less ‘well-behaved’ than the Sun • Rises in different places and much different times every night, if it was visible at all • Changed shape as well, unlike the unchanging Sun

17. Phases • The Moon appears to change shape because of its position relative to the Earth and the Sun • In the bottom right there seems to be a problem; the Moon is there however! • The cycle takes about 29 days, an interval known to the ancients

18. Briefly;

19. Patterns in the Night • Constellations: “stars together” • Different for different cultures (following slides) • Fanciful at best, but a good mnemonic to find things • Useful for calendars

20. Special Constellations • Zodiacal • 12 Astrological signs • Misleading: the sign is not up at night during its reign • Circumpolar • Never set • Useful for navigation

21. Two Western Constellations Orion is facing backwards for use with a celestial sphere

22. Egyptian Sky (interpretation of Greek view)

23. African Sky • Used the sky to explain myths

24. Chinese star map from the Tang Dynasty

25. Calendars (snapshots, only for comparison) • Egyptian • 360 + 5 days • Sothis • 3 seasons • 3 10-day weeks • Babylonian sexigesimal system • 360 days, 12-30 day months, 4 seasons • Begins with crescent Moon

26. Greek • 4th C. BC • Months 1-4 36 days, 5-10 35 days each • Roman • 12-month 355 day year • D days per month • Mensis Intercalaris month of 27 days • Chinese • 12 Lunar months with alternating names • Mayan • Many variants that synchronized, e.g. 260 day Tzolkin with 365 day Haab • Also lunar and Venusian cycles

27. Modern Western • Established by Pope Gregory 1582 • Threw out lunar influence (almost) • 365.24 days • Leap year rules • Still corrected for atomic clocks

28. Days of the Week • Like calendars, each culture had different names for the days of the week, number of days in a week, and number of hours in a day • Western names derive from celestial objects • English names span several languages

29. Sundials • The oldest known instruments for keeping track of time • First attempt at marking time ~ 5000 BC • 2500 BC: Babylonian and Egyptian obelisks • By 250BC the Greeks produced complex and more accurate sundials using their knowledge of geometry

30. Examples

31. Visitors in the Sky • The First UFOs! • Unpredictable, irregular • Shooting Stars • Not! Small grains of dust • Comets • “Bad Star”: Dis-Aster • Harbingers of catastrophe

32. Why Astrology is Not a Science • Vague, untestable • No account for time delay • Wide constellations • Twins