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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