Astronomy 350L (Fall 2006)
The History and Philosophy of Astronomy (Lecture 2: Beginnings: Prehistory, Egypt, Babylon)
Instructor: Volker Bromm TA: Jarrett Johnson The University of Texas at Austin
The Beginning of Astronomy
• Po Poss ssib ible le Mot Motiv ivat ation ions: s: - Relig Religion, ion, creat creation ion myths, myths, sta state te ideology ideology - Tim Timing ing of importan importantt events: events: rituals rituals,, agricultur agriculture e calendars - Navig igat atiion -…
• Ea Earl rly y Ast Astro rono nomy my:: - Preh Prehisto istory ry (e.g., (e.g., Stone-Age Stone-Age Britain) Britain):: no written written record we can only speculate - Anc Ancien ientt Egyp Egypt: t: ca calen lendar dar (t (to o predi predict ct Nil Nile e floo flood) d) - Meso Mesopota potamia/B mia/Babylo abylon: n: sear search ch for patt patterns erns diligent gatherers of data
The Naked-Eye Sky: Basic Facts
Earth’s daily rotation
celestial sphere moves East to West
Daily motion of the stars
No change in relative positions
fixed stars
Quick reminder: Why does concept of celestial sphere work (from our present-day perspective)? perspective)?
Trop Tr opic ic vs Tem Tempe pera rate te Sk Sky y
Tropical Location (e.g., Northern Yucatan)
High-latitude Location (e.g., Britain)
The Naked-Eye Sky: Basic Facts
Earth’s annual motion around Sun: - in pl plane ane of th the e ecl eclipt iptic ic - Earth’s axis of rotation rotation is skewed skewed toward toward eclipti ecliptic c plane plane
Earth-Sun motion on Celestial Sphere:
Sun moves along ecliptic once a year!
Sun’s apparent motion and Seasons
Trop Tr opic ic vs Tem Tempe pera rate te Sk Sky y
Tropical Location (e.g., Northern Yucatan)
High-latitude Location (e.g., Britain: Stonehenge)
Trop Tr opic ic vs Tem Tempe pera rate te Sk Sky y
High-latitude Location (e.g., Britain: Stonehenge)
Tropical Location (e.g., Northern Yucatan)
The Naked-Eye Sky: Basic Facts
Lunar Cycle: ~29.5 days to reach same phase again!
Naked-Eye Sky: Irregular motion of planets
• Ret Retrogr rograde ade motio motion n of plane planets, ts, oppos opposite ite direction to daily motion (E-W) of celestial sphere
Prehistory: Alignment Astronomy
Callanish, Hebrides (ca 3,000BC)
Megalithic structures Full moon rises in this location once every 18.6 years!
Prehistory: Alignment Astronomy
Stonehenge
Late Neolithic-Early Bronze Age (ca 3,000 -1,000 BC)
Prehistory: Alignment Astronomy
Architecture reflects cosmic symbolism! But was was it a neolithic neolithic “pre “precis cision ion observa observatory tory”? ”?
Prehistory: Alignment Astronomy
(Gerald Hawkins, 1965)
Was it it a neolithi neolithic c “pre “precis cision ion observ observato atory” ry”? ? Probably not!
Dawn of Civilization (and of recorded history)
(~ 5, 5,00 000 0 – 3, 3,00 000 0 BC) BC)
Ancient Egypt
Pre-eminent concern: Predict Nile flood need reliable calendar!
Ancient Egypt: Calendar • Bas Basic ic Proble Problem: m: Day, Day, month month and year year are are no simple simple multiples of each other!
- Sy Syno nodic dic (p (pha hasese-toto-pha phase se)) mont month h = 29 29.5 .5306 306 da days ys - Tro Tropic pical al (equi (equinoxnox-to-e to-equin quinox) ox) yea yearr = 365.2422 days
Ancient Egypt: Calendar • Big idea: Fix time (define zero-po zero-point int of of calendar calendar by utilizing heliacal rising of Sirius! Moment of Sunrise:
Da y 1
Day 2
Day 3
Heliacal rising
For Sirius (Dog Star): late July
close to Nile floo
Ancient Egypt: Calendar • Bi Big g ide idea: a: Ut Utililiz ize e heliacal rising of Sirius! -demand: Sirius always must rise in 12th month! -if Sirius were to rise late in 12 th month, add extra (13th) month intercalation -then: 365 = 12x29.5 + 11 sequence: 12-12-13 12-12-13-12-12-12-12-13 13-… -… • Eg Egyp ypti tians ans had had two two cale calenda ndars rs religious (see above) and administrative: 12x30 days + 5 extra days = 365
Mesopotamia Birth Bi rthpl place ace of of:: - wr writ itin ing g (cuneiform) - ad adva vanc nced ed ari arith thme meti tic c (se sexa xage gesi sima mall sy syst stem em) - fi firs rstt writ writte ten n law law code code (Hammurabi) - fi firs rstt know known n lite litera ratu ture re (Epic of Gilgamesh)
mathematics
astronomy
Neo-Babylonian=Chaldaean
Mesopotamia: Advanced Arithmetic
1x603+57x602+46x60+40
- sex exag ages esiima mall sy syst stem em (b (bas ase e 60) 60) - adv advanc anced ed place-va place-value lue syste system m (like (like our base-10 base-10 one) one)
Mesopotamia: Advanced Mathematics - “P “Pyt ytha hago gore rean an th theo eore rem” m” (~ (~1, 1,70 700 0 BC BC))
1.414213
Mesopotamia: Systematic Astronomy - Pa Pati tien ent, t, long longter term m re reco cordi rding ng of cel celest estia iall posi positi tion ons s (moon, Sun, planets…) - Sea Search rch for pat pattern terns/r s/regul egularit arities ies - Ca Cata talo log g of of om omen ens: s: Enuma Anu Enlil
More than 7,000 omens recorded
Mesopotamia: Systematic Astronomy • Metonic Cycle: (nam (named ed after after Meton Meton of Athens Athens,, 432BC) 432BC) -19 tropical years = 6939.602 days - 23 235 5 sy syno nodi dic c mo mont nths hs = 69 6939 39.6 .688 88 da days ys Introduce 7 intercalary months per 19-year cycle [19x12 + 7 ~ 235]
Mesopotamia: Systematic Astronomy • Saros Cycle:
eclipse cycle (~18 years)
Mesopotamia: Systematic Astronomy • Saros Cycle:
eclipse cycle (~18 years)
The Beginning of Astronomy:
• Pr Preh ehis isto tory ry:: - Ali Align gnmen mentt ast astron ronomy omy - no wri writt tten en rec recor ords ds all inferences tentative
• An Anc cie ient nt Egy Egypt pt:: - ast astronom ronomy y serves serves overruling overruling need need to time time Nile flood flood - Cons Construc truction tion of sophisticat sophisticated ed calendars: calendars: intercalat intercalation ion - He Helia liacal cal ris rising ing of Siri Sirius us
• Me Meso sopot potami amia/ a/Bab Babyl ylon: on: - soph sophisti isticate cated d math mathemat ematics: ics: sexagesi sexagesimal, mal, place-valu place-value e arithmetic, algebra - num numerica erically lly prec precise, ise, long longterm term reco recording rding of cele celestial stial patt patterns erns Enuma Anu Enlil ta tabl blet ets, s, Me Meto toni nic c an and d Sa Saro ros s Cy Cycl cles es
