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History of Astronomy (1200) ALL Lecture Notes
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Full semester of history of astronomy lecture notes.
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Voorbeeld van de inhoud
WhatWe Already Know About the Universe:-Earth is round!!
-Sun is ordinary star in galaxy, not even center of milky way
-Stars sustain themselves by nuclear fusion: come into being and
end their lives over various time scales
- There are other planetary systems around other stars in the
milky way
- Universe is expanding
- Universe started from the big bang
Chapter 2 Astronomy in Antiquity:
- Basic movements in sky (sun rising and setting, fixed stars,
stars shifting every night
- The “wanderers”- planets not shifting like stars
- Astronomy in antiquity focused largely on moving objects in
sky=the sun, the moon, Mercury, Venus, Mars, Jupiter, Saturn
(the five lesser planets)
- Until 18th C astronomers had 2 goals- 1-show movements of
planets were regular and had patterns, 2-accurately predict
their movements
Historical Resources:
- Babylonian clay tablets
- Greek scripts (on less durable materials-not many)
- Most historical records did not survive-some vanished because
their materials did not last, some disappeared because writings
were wrong and had lost their value
Astronomy in Babylon & Egypt:
Mesopotamia (Babylon)= land between rivers
- Complicated history
- Sumerians- 5000 BC, 1st humans formed civilization, created
city states, invented writing, inscribed on clay tablets,
invented math and numbers
- Akkadians- replaced Sumer 2330 BC
- Asyrians- rose to power in north 1900 BC
- Babylonians- King Hammurabi conquered Mesopotamia (1792-1750
BC)
- Asyrians- once again rose to power (1225) captured Babylon
- Neo-Babylonian- King Nabopolassar took back Babylon (616 BC)
- Persian- Cyrus the Great began Persian Empire (550 BC) and took
city of Babylon
- Macedonian- Alexander the Great conquered the land and the
Persian empire (333 BC)
- Most advancements made by babylonians and sumerians
- Sexagesimal notations (1 to 60- time)- invented by babylonians;
seen in astronomy records
,Babylonian Astronomy Records:
- Babylonians systematically observed and recorded astronomical
and other natural phenomena, which went on for more than a
millennium
- Enuma Anu Enlil- set of 68/70 tablets recording 6500-7000 omens;
signs to the king- astrological need drove these observations and
recordings; tablets record phenomena related to moon, sun,
weather, earthquakes, planets, and stars
- Anu- Sky Father, king of gods, lord of constellations
- Enlil- god of wind, air, earth
- Records became invaluable resource for later astronomers; helped
identify regularity in movements of celestial bodies
Babylonian Calendar:
- Intercalary month- needed in their culture (like a leap year,
with an additional month)
- Metonic cycle- 19 solar years, close to 235 lunar months, added
7 more months every 19 years
- Day: the time elapsed between the sun reaching its highest point
in the sky two consecutive times (solar day)
- Month: when the moon completes a full cycle of its phases
(lunar/synodic month=29.5 days)
- Year: period which the sun returns to the same position (the
highest or lowest latitude)- tropical year- 365.25 days
- All definitions depended on observations
How We Do It Today:
- “Leap year”- solar year is 365.25 days, one regular calendar
year is only 365, we need one leap year every four years to
compensate; this is deeply rooted in what babylonians did
Beginning of Ephemerides:
- Astrologers needed tables (“ephemerides”) to predict the
positions of the sun, moon, and other planets so they could
carry out business regardless of weather
- Babylonians were able to create tables because of observations
and their numbering system
- Tradition of ephemerides has been carried on through today
- Babylonians tracked moving speed of sun, moon, and other
planets: had two ways to approximate: sun moved with one
constant speed for one half of year, and a different constant
speed for the second half; OR sun increased speed uniformly
month by month for one half of the year, decreased for the
other half
- Babylonians cared about HOW not WHY
Ancient Egypt:
- Numerals- base 10 system w/symbols
, - development of astronomy set behind by lack of a proper
numbering system
- Introducing constellations (decans) was drove by need of timing
- A sequence of 36 decans were selected on the sky, which rose at
regular intervals on any given night, like a stellar clock
- Ancient egyptian life revolved around the flooding of the Nile
river on an annual basis; divided the year into 3 seasons
(Akhet- flooding, Peret- growth, Shemu- harvest), but when
using 12 lunar months, yearly cycle would not match 3 seasons,
had to give one of the seasons a fifth “intercalary” month
- Using Sirius to “control” the seasonal year to be in sync with
the solar year
- Administrative calendar- based on solar year; avoided varying
varying number of days & months; only 360 days, added an extra
5 to the last month; calendar year and seasonal year became out
of sync; convenient for astronomers
Ancient Greece:
- Various city states were established
- Developed societies required timing and calendar, all tied to
astronomical observations
Astronomy in Early Ancient Greece:
- Ancient greek people developed their own calendars, chaotic
because each city state had its own calendar
- Conceivable that ancient Greece had some contact with Egypt and
Babylon, influences from both existed- astronomers recorded
celestial phenomena using Metonic cycle, usages of 12 zodiac
signs, etc
- Greek astronomy was distinct in its unique way of thinking and
reasoning
Unique Greek Thinking:
- Understanding of the universe, very abstract
- Greeks were more satisfied with being able to explain why,
seeking material unity, building models
- Weakness: not super precise all the time
- Biggest step forward: concept of sphere
- Thales of Miletus: 1st philosopher, 1 of seven wise men;
believed that every changing thing was governed by water;
correctly interpreted eclipses
- Anaximander of Miletus: one of 1st cosmologists: sun was highest
heavenly body, then moon, then stars; Earth was a cylinder,
center of universe; fixed stars were wheel-like condensations
of air filled with fire; wrong ideas, but marked an important
shift: there was a mechanical law behind the operations of the
universe
Pythagoreans and Spherical Earth:
, - Pythagoras of Samos: credited with numerous discoveries and
thoughts; core belief in numbers
- Most influential thought: relation between arithmetic ratios
and harmonic interval of music & Earth is a sphere
- Aristotle’s proofs:
- Lunar eclipse: the shadow that the earth casts on the moon is
always circular
- When travelling north to south, one would see different stars
- Corollary: the Earth’s size cannot be very large as compared to
the heaven
Pythagoras’ Cosmos:
- Natural world should be a cosmos-complex system of natural
order
- First time that universe was treated as an entity
- Cosmology today= discipline that studies the behavior of the
universe as a whole
The Spherical Universe:
- Extending the idea of a spherical Earth--the universe is made
of spheres (visible or not)
- This perception of universe was further developed by Plato and
Aristotle
- Aristotle’s “five elements” became the underlying operating
mechanics of the universe
- Aristotelian cosmology “drew strength from being an
intellectual formalism that reinforced common senses”
Socrates, Plato, Aristotle:
- Socrates: philosopher, did not leave any written text; lives on
as a character in Dialogues of plato; difficult to separate
their thoughts
- Plato: philosopher, founder of the Platonist school, and the
Academy; greatly influenced by Pythagoreans
- Platonism believed that the material world is not a reality- it
is just an ever-changing image of the real world; the latter
being made of unchanging, abstract objects
- Aristotle: student of Plato, philosopher, greatly impacted
Western culture; Earth is a sphere, universe is larger sphere
around it (geocentric model); terrestrial world different from
heavens; perceptions of terrestrial elements-put in fifth
element- aether- “quintessence”, makes all the heavenly bodies
Stationary Earth & Consequences:
- Aristotle asserted that the Earth must be at rest, which is
fully consistent with everyone’s sense
How the Planets Move:
- Sun and moon were considered planets
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