time keeping early structures to mark time
TRANSCRIPT
Beginnings of Astronomy
Overview of Chap02a
!!Time KeepingTime Keeping
!Early Observatories
!Early Records
!Early Myths
!Earth centered Model
!Ancient Greek
Astronomers
! Heliocentric Theory
(Sun-Centered Model) " Seasons marked by equinoxes and solstices were important dates
for agriculture and hunting;
" Motion of the Sun, the Moon and stars tracked the time of day and
night for orientation and later navigation needs.
" The planets were known out to Saturn. Their wandering motion
made them distinct from the fixed stars.
Beginnings of Astronomy Time of Day ---Time of Day ---
Position of the SunPosition of the SunTime KeepingTime Keeping
Time of Year--
Position of Sun
relative to the horizon
and the Constellations
Local herders built a
stone circle on the
shoreline of a lake
that has long since
dried up. The stone
slabs three meters
high were dragged
over a kilometer to
create the site
marking the
solstices.
Nabta Early structures to
mark timeSouthern Egypt
! 6000 BC
Aubry holes ring of 56 holes,
Movement of a marking stone
would complete a circle in 18.67
years -- approximately the
period for the "nodes", needed
to predict the eclipses
Stonehenge ( 3000-2000 BC)English county
of Willtshire
Summer
Solstice
Sec 2.1
Ring of Sarsen
Stones
33 meters) in
diameter
Heel Stone on
midsummer's morning
the sun rose directly
over the Heel Stone
and the first rays
shone into the centre
of the monument.
-- a temple and/or astronomical calculator?.
SW United States: “Sun Dagger” marks summer solstice
"Spokes of the Big Horn Medicine Wheel built approximately 1050 AD by
the Lakota Native Americans
"aligned with rising and setting of Sun and other stars
"its 28 "spokes" may symbolize the days in a lunar month.
The "Caracol" at Chichén Itzá is
believed to have served as
an observatory( ! A. D. 600-850).
Certain doors and windows line up with
various planetary orbits.
Sec 2.1
Early Record: Babylonian
Tablet with a list of eclipses
between 518 and 465 B.C.
Around 4000 B.C: The oldest astronomical observations ever recorded
(Egypt and Central America)
Around 3000 B.C: The first written materials on astronomy (Egypt, China,
Mesopotamia and Central America)
2697 B.C.: The oldest preserved relation on the Sun eclipse (China)
Around 2000 B.C.: The first solar-lunar calendars in Egypt and Mesopotamia
Early Time Line
Tablet containing the text of Enûma Elish 12th
century BC
The Enuma Elish "When on High . . .”
The Mesopotamian/Babylonian Creation Myth
recounting the struggle between cosmic order
and chaos.
Early Myths of the Origin
In ancient Egypt the dome of
the sky was represented by
the goddess Nut, who
arched her back over the
earth so that only her hands
and feet touched the
ground. The sun god Ra
was born from her every
morning.
From Myths to Scientific Models
Thought that natural phenomena -
including the heavens - could be discussed
as processes governed by natural laws,
rather than relying on supernatural
explanations.
Scientific Method
Thales of Miletus 624- 547 BC
Thales of Miletus 624- 547 BC Model of the Universe
"In the beginning there was only water, that the world and all things were
composed of water. “Water” in this context was some unifying principle.
"The Earth was a large (flat) disk floating on an infinite ocean of water,
and that earthquakes resulted from disturbances in this ocean that shook
and cracked the Earth.
Aristotle
(384-322 BCE)
Ptolemy
(85 -165AD)
Thales of Miletus
624- 547
Ancient Greek Astronomers
Aristotle
(384-322 BC )
Claudius
Ptolmey
A.D. 85-165 Plato
427-347 BC
Thales of
Miletus
624- 547
BC
Pythagoras
560-500 BC
The father of Greek
mathematics
Entire universe can be
described in numbers
Systematized logic,
which forms the
basis of
western science
Jupiter
Venus (right)
The Greeks distinguished planets from stars because of their ‘wandering
paths’ through the sky (“planets” from ‘wanderer’ in Greek)--- Mercury,
Venus, Mars, Jupiter & Saturn plus the Sun and Moon
“Wandering Stars”
Saturn
(left),
Mars (top),
General Observations of the PlanetsTo naked eye, planets look like stars, but they change their position
relative to the other stars. Greeks called them "wandering stars" Motion
somewhat like sun and moon
#They were carried by the celestial
sphere from night to night with the
fixed stars.
#However, in addition they had
their own motion and they followed
their own circle path through stars.
#Each planet had its own period for
its circular path through stars.
#Planets sometimes reverse course
relative to stars, RETROGRADE
motion.
The Planets were objects of !perfect" shape andmoved on perfect paths, i.e., spheres and circles.
Greek Astronomy
Heavenly bodies were unchanging and perfect
wandering stars: Mercury, Venus, Mars,
Jupiter & Saturn plus the Sun and Moon
The 7 planets and the stars all moved in perfect
circular orbits, with perfectly uniform speeds.
The earth was spherical and placed it at the
center of the Universe.
Aristotle
(384-322 BC )
Celestial motion
Heavenly bodies are
perfect spheres and
move on perfect
circles
The orbit of the
moon separated the
imperfect terrestrial
realm from the
perfect heavens
AST121,
Robert Zimmerman
University of Oregon
• All planets generally moveeastward with respect tothe background of stars.This is called progrademotion
Retrograde motion is
westward
primary motion is
eastward
When planets reverse
direction and move
westward w.r.t. stars: this
is retrograde motion
Problem with circular motion:
Retrograde
Motion
Claudius Ptolemy A.D. 85-165
Used EPICYCLES to account for
retrograde motion
! In his great 13-booktreatise, the Almagest,Ptolemy presents hiswork on the path of theSun, the Moon, and thefixed stars.
! Ptolemy’s geocentricuniverse accuratelypredicted the motion ofthe planets with ageocentric model withcircular orbits.
! This was the bestmodel of the cosmosuntil the late 15th
century.
Claudius Ptolemy A.D.
85-165 the Almagest,
Ranked by
how long
they took to
make a
complete
cycle
Moving Earth
(Heraclites, BC 387-312) Earth rotateson its axis
(Aristarchos BC 310-230) Sun-centred solar system
1. Earth “feels” stationary. Wouldn’t
clouds, air, birds, etc. be left behind if
the Earth were moving?!
Observation against a moving
Earth
No stellar parallax could be measured ---
Hipparchus tried very hard! (150 BC)
The first stellar parallax was measured in
1838 by Friedrich Bessel
2. No Stellar Parallax
Eratosthenes (267-194 BC)
noticed that when Sun was
directly overhead in one city, it
was at an angle in another
Measuring the angle and the distance
between the cities gives the radius.
7.2/360= dist/circum
Measuring Earth’s radius
7.2
Measurement: R! 6366 km
Today’s Value
R! 6378 km---(! 2-20 %)
! Arabs conquered many of
these countries starting in the
7th century, and preserved a
lot of the work done by the
Greeks
! Religious motives required
accurate timekeeping and
astronomical observations
! Translated Ptolemy’s
Almagest into arabic. It
contained a catalogue of over
1,000 stars that were given
arabic names
! The Almagest became the
foundation and ideas for the
15th and 16th centuries.
Islamic Period: 700-1300 AD
Galileo Galilei
(1564–1642)
Argued for Copernicus’
Model
Isaac Newton
(1642 – 1727)
Law of Gravity
Tycho Brahe 1546 -1601
Pre-Telescopic Measurements
Nicolaus Copernicus
1473-1543
Sun-Centered Model
Johannes Kepler
1571 - 1630
Three Laws
Heliocentric Theory:
Planets move around
the Sun rather than the
Earth
In the book, Copernicus stated that
1. the Sun was the center of the universe and
that the Earth had a double motion around
this center.
2. Copernicus still retained the circular motion
for the orbits
3. He argued that his system was more elegant
than the traditional geocentric system.
4. All the Planets revolve around the Sun!
5. Stars are very much farther away than the
Sun-----the parallax motion is too small
to observe
Nicolaus
Copernicus
1473-1543
A stationary Sun and moving Earth clashed with many biblical passages.
Protestants and Catholic alike often dismissed heliocentrism on these
grounds. The book’s preface stated that the theory put forward in this book
was only a mathematical hypothesis.
Heliocentric Universe
Spent his life as a physician, lawyer, and
church administrator. He wrote
De Revolutionibus Orbium Coelestium,
("On the Revolutions of the Celestial Orbs"),
which was published in Nuremberg in 1543, the year of his
death.
Retrograde motion had a natural explanation
CopernicusCopernicus
Tycho Brahe (1546-1601)# made precise observations before the
invention of the telescope.
Sec 3
#His observations of planetary motion,
particularly that of Mars, provided the
data for Kepler to construct his three
laws. Carefully measured the orbit of
Mars for 20 years
#He made observations of a supernova
in 1572 and a comet in 1577.
#Hired Kepler as an assistance in 1600.
oThe"star" appeared suddenly where none had
been seen before and was visible for about 18
months before fading from view.
oBrahe's observations showed that the
supernova did not change positions with
respect to the other stars (no parallax).
Therefore, it was a real star, not a local object.
Observed a new star (Supernova) in 1572
!This contradicted the teachings of
Aristotle, who had held that comets
were atmospheric phenomena ("gases
burning in the atmosphere" was the
common explanation among
Aristotelians).
! Supernovae and comets
represented an obvious change on the
celestial sphere that was supposed to
be unchanging
Observed a comet in 1577
By measuring the parallax for the
comet, he was able to show that the
comet was further away than the Moon.
" Born in Germany in 1584
" in 1589 he began his university education at
Tübingen where he studied theology
" In 1597 Kepler published, The Cosmographic
Mystery, in which he explain the relative
distances of the planets from the Sun in the
Copernican System.
" Because of his talent as a mathematician , Kepler
was invited by Tycho Brahe to Prague to become
his assistant. Kepler moved to Prague in 1600.
" Kepler served as Tycho Brahe's assistant until
the latter's death in 1601 and was then appointed
Tycho's successor as Imperial Mathematician, the
most prestigious appointment in mathematics in
Europe.
" In 1609 he published his first two laws and in
1619 he published the third law
Johannes
Kepler
1571 - 1630
Kepler’s First LawThe orbits of planets are ellipses, with the Sun at one
focus and nothing at the other focus.
Focus
• Major Axis
• Minor Axis
• Semi-Major Axis (a)
Ellipse perihelionaphelion
0.2 .007 .017 .09 .048 .056 .046 .01 .25
Mer Ven Earth Mars Jup Sat Ur Nep Pluto
a( 1-e)
-------------------------------------------------------a( 1+e)-----------------
a( 1+e)
x
------------------ a------------------------
----
2nd Law: Orbiting objects sweep out equal areas in equal times
speed of planetsspeed of planets
- fastest at perihelion, slowest at aphelion- fastest at perihelion, slowest at aphelion
Kepler’s Third Law
61,500.61,600.248.39.5Pluto
27,200.27,300.165.30.1Neptune
7,060.7,080.84.019.2Uranus
870.868.29.59.54Saturn
142.141.11.95.20Jupiter
3.533.511.881.52Mars
1.001.001.001.00Earth
0.3780.3780.6150.723Venus
0.0580.0580.2410.387Mercury
P2a3P (year)a (AU)Object
aAU3 = PYr
2Kepler’s Third Law outer planets move slower
Galileo Galilei (1564-1642)
• Dutch invent telescopes
in early 1600’s
•Galileo learns of the
invention and within a
month --- he creates his
own.
• Galileo was the first to
use the telescope for
science observations.
1. Milky Way
2. “Spots” on the Sun!
3. The Moon has mountains,
craters, rocky surface with
imperfections!
4. The “planet” Jupiter is not a
pinpoint star – but a disc in the
sky! WITH MOONS!
5. Saturn is not round!
6. Venus has “PHASES” like the
MOON!
Galileo Galilei (1564 Galileo Galilei (1564 –– 1642) 1642)
1610 “Siderius Nuncius” (The Starry
Messenger)
The results were astounding,
and completely at odds with
what most people thought
about the universe.
Milky Way
Saturn
Milky Way: Objects exist that
Aristotle knew nothing about - the
combined light of many faint stars
can produce an observable result.
Sunspots: “Spots” on the
Sun! Showed they were on
the Sun and not in the
atmosphere.
Sunspots
Saturn: He thought the rings were "handles" or largemoons on either side of the planet. He said
"I have observed the highest planet [Saturn] to betripled-bodied. This is to say that to my very greatamazement Saturn was seen to me to be not a singlestar, but three together, which almost touch eachother".
it was not a perfect
sphere as he had
been taught, but
rough and mountainous.
The Moon
It was clearly made
of solid stuff and
was another world.
Four objects that do not
orbit the Earth.
Sec 3
Phases of Venus cannot be explained by geocentric model
The full phase cannot
happen in the
Geocentric Model
Copernican
Model
Heliocentric Model--Phases of Venus
--Phases of VenusGeocentric Model
Dialogue
Concerning the
Two Chief World
Systems 1632
1632: wrote the Dialogue Concerning the Two Chief
World Systems which was written as a dialogue between
two spokesmen, one for Copernicus, and the other for
Aristotle. He completed the Dialogue in 1630, and tried to
get it published, but could not. It was eventually printed
in March 1632.
1616: Galileo was instructed
to give up holding or defending
the idea that 'the sun stands still
at the centre of the spheres
while the Earth is in motion'.
A few copies were circulated, and then the printer received an instruction
to halt all further printing and Galileo was to appear before the
Inquisition.
1642: He died in 1642 -
the year Isaac Newton
was born.
Galileo was forced to
confess his views
and to condemn
them. He was
sentenced to
permanent house-
arrest at his villa at
Arcetri near Florence
villa at Arcetri near Florence
Aberration of starlight:
Discovered by the English astronomer James
Bradley and explained by him in 1729. The
phenomenon is caused by the orbital motion of the
earth
Analogy---vertically falling
raindrops appear to fall
diagonally when viewed by a
moving person.
Telescopes must be tilted
on moving Earth
100 years later (1729)--Proof that the
Earth Orbits the Sun
In 1851, Jean-Bernard-Leon
suspended a Foucault pendulum
from the dome of the Pantheon in
Paris.
dome of the
Pantheon in Paris.
200 years later (1851)--
Proof that the Earth Rotates
The plane of its motion, with respect to the earth, rotated
slowly clockwise.
This motion is produced by a rotating earth.
End of Chapter 2a
The Copernican Revolution
Go to Chapter 2b