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The History of Astronomy
The History of Astronomy
Earliest astronomical record: a lunar calendar
etched on bone from 6500 B.C. Uganda.
Also we find early groups noted the Sun,
Moon, Mercury, Venus, Earth, Mars and
Jupiter
felt certain alignments of the
stars and planets caused the
Nile to flood
Pyramids aligned (N S E W)
Pyramid shafts align with
specific constellations
believed to make an early
sun dials.
Egyptians
British Isles
Stonehenge (3100 BC
- 1500 BC) is aligned
with the movements
of celestial objects.
The Chinese
developed a
working calendar
and kept careful
track of comets,
eclipses and sun
spots.
Early Chinese Star Chart
Chinese Oracle bones
contain records of
novae and comets.
The Mayan
developed a very accurate
calendar, later adopted by the
Aztecs.
accurately predict solar and
lunar eclipses.
This structure, called the
Caracol, at Chitzen Itza may
have been used as a Venus
Observatory
Dresden Codex
Aztec Calendar
The Caracol
Ancient Greeks
By 500 BC, the Greeks had constructed a model that describes the motions of the sky.
Geocentric model Spherical Earth at the center of
the universe Sun, Moon, and planets
surrounded us on perfect spheres.
EARLY GREEK ASTRONOMY
Shape of Earth (circa 400 BC)
EARLY GREEK ASTRONOMY
Shape of Earth (circa 400 BC)
Size of Earth (Erastothenes
circa 200 BC)
EARLY GREEK ASTRONOMY
Shape of Earth (circa 400 BC)
Size of Earth (Erastothenes circa 200 BC)
Distance to the Sun
Assumptions of Early Models
Geocentric - Earth in the middle
Everything orbits the Earth
Stars are located on the Celestial Sphere
Everything moves in uniform circular motions
Aristotle ~350 BC
Earth at the center of the Universe
Earth was round due to gravity All heavy things
sank, thus the stars and planets had to be lighter than the air.
Ptolemy 85-165
Earth was at the center of the
Solar System - Geocentric Model
Used epicycles to explain
retrograde motion.
Earth
Mars
deferent epicycle
Equant
Center
Nicolaus Copernicus
(1473-1543)
Heliocentric system!
Explains –
phases of Moon
Retrograde motion
Not very accurate
Tycho Brahe (1546-1601)
Observations of comet
Observation of supernova – far away
Naked eye observations of planets
Best observations of planetary positions
Johannes Kepler (1571-1630)
Worked for Brahe
Took data after his death
Spent years figuring out the motions
of the planets
Came up with…
Three Laws of Planetary Motion
Ellipses
Kepler’s 1st law:
All planets orbit the Sun on an ellipse, with
the sun at one focus.
Kepler’s 2nd Law
As a planet moves through its orbit, it sweeps out
equal areas in equal times.
Planets move:
•Fast at perihelion
•Slow at aphelion
Kepler’s 3rd law
More distant planets orbit the Sun at slower
speeds than closer ones.
Works for
asteroids, comets,
and everything
orbiting the Sun!
Period 2
Semi - major axis 3Constant
Galileo Galilei (1564-1642)
Knew of Copernicus’ & Kepler’s work
Used a telescope to look at the sky
The Moon was an imperfect object
Venus has phases
Jupiter has objects around it
Saturn is imperfect
The Sun is imperfect
Cassini 1625-1712
Saturn's Rings are split into
two parts, "Cassini Division".
Jupiter’s Great Red Spot
Observed “differential rotation” in gas planets
Isaac Newton (1642-1727)
The ultimate “nerd”
Able to explain Kepler’s laws
The Three Laws of Motion
1. Law of Inertia - Objects do whatever they are currently doing unless something messes around with them.
2. Force defined
F=ma
F=force
m=mass
a=acceleration (change in motion)
3. For every action there is an equal and opposite reaction.
Edmond Halley 1656-1742
predicted a comet's return - every 76 years.
William Herschel 1738-1822
discovered the planet Uranus
Christian Doppler 1803-1853
Theorized that waves from a
moving source would be
compressed or expanded.
Doppler Effect
Albert Einstein 1879-1955
Einstein presented his
specific theory of relativity
E=mc2
Light can bend
Time slows as you near the
speed of light
Edwin Hubble 1889-1953
expanding universe theory.
Gerald Kuiper 1905-1973
belt of comet-like debris at
the edge of our solar system.
Kuiper Belt
Carl Sagan 1934-1996
search for extraterrestrial intelligence.
Stephen Hawking 1942-Present
study of black holes