Transcript The Origin of Modern Astronomy

The Origin of Modern Astronomy
Why did people look up?
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Religion
Navigation
Time keeping (calendar, clock)
Food (planting, hunting, breeding)
The Roots of Astronomy
• Already in the stone and bronze ages, human
cultures realized the cyclic nature of motions in
the sky.
• Monuments dating back to ~ 3000 B.C. show
alignments with astronomical significance.
• Those monuments were probably used as
calendars or even to predict eclipses.
Stonehenge
Summer solstice
Heelstone
• Alignments with
locations of sunset,
sunrise, moonset
and moonrise at
summer and winter
solstices
• Probably used as
calendar.
• Constructed: 3000 – 1800 B.C.
Other Examples All Over the World
Big Horn Medicine Wheel (Wyoming)
The Roots of Astronomy
Newgrange, Ireland, built around 3200 B.C.:
Sunlight shining down a passageway into the central chamber
of the mount indicates the day of winter solstice.
Other Examples All Over the World (2)
Caracol (Maya culture, approx. A.D. 1000)
Other Examples All Around the World
Chaco Canyon,
New Mexico
Slit in the rock formation
produces a sunlit
“dagger” shape, indicating
the day of summer
solstice
Other Examples All Around the World (2)
Mammoth tusk found at Gontzi, Ukraine:
Inscriptions probably describing
astronomical events
Ancient Greek Astronomers (1)
• Unfortunately, there are no written
documents about the significance of
stone and bronze age monuments.
• First preserved written documents
about ancient astronomy are from
ancient Greek philosophy.
• Greeks tried to understand the motions
of the sky and describe them in terms
of mathematical (not physical!) models.
Ancient Greek Astronomers (2)
Models were generally wrong because
they were based on wrong “first
principles”, believed to be “obvious” and
not questioned:
1. Geocentric Universe: Earth at the
Center of the Universe.
2. “Perfect Heavens”: Motions of all
celestial bodies described by motions
involving objects of “perfect” shape, i.e.,
spheres or circles.
Thales of Miletus
lived from about 624 BC to about 547 BC
Founder of Greek Science
Suggested that supernatural explanations were not necessary to understand what the
universe was made of.
Suggested that the world was inherently understandable and not just the result of
arbitrary or incomprehensible events.
Thales’ Cosmos
water
Air
water
earth
Thales’ believed the universe consisted fundamentally of water with
Earth as a flat disk on an infinite ocean.
This was not widely accepted.
Anaximander
of Miletus
610-c. 547 BC
Student of Thales.
Suggested that the heavens must form a complete
sphere around Earth (to explain the sky turning around
the north star).
Based on how the sky changes with travel north and
south, he concluded that Earth must not be flat.
Because the sky didn’t change with east-west travel, he
guessed that Earth might be a cylinder curved only in the
north-south direction.
Anaximander’s Cosmos
Ring of Fire
air and clouds
Horizon
Horizon
Earth (a cylinder)
Underground home of the heavenly bodies
Because the sky didn’t change with east-west travel, he guessed that Earth might
be a cylinder curved only in the north-south direction.
Pythagoras of Samos
lived from about 569 BC to about 475 BC
Taught that Earth was a sphere.
Pythagorean Theorem
C
A
B
a2 + b2 = c2
“Nothing exists but atoms and empty space. Everything else is opinion.”
Democritus of Abdera
lived from about 460 BC to about 370 BC
Democritus was a student of Leucippus. Together they are
considered “co-originators” of the belief that all matter is made
up of atoms.
He said that atoms were eternal, invisible, indivisible, and
incompressible.
Democritus believed the universe was made of an infinite
number of atoms of the four elements.
He claimed the moon had mountains and valleys, the Milky Way was a vast group
of individual stars, and that Earth and other worlds were created by random
motions of infinite atoms. Other philosophers, including later Aristotle, argued
against this.
Democritus was among the first to propose that the universe contains many worlds,
some of them inhabited:
"In some worlds there is no Sun and Moon while in others they are larger than
in our world and in others more numerous. In some parts there are more
worlds, in others fewer (...); in some parts they are arising, in others failing.
There are some worlds devoid of living creatures or plants or any moisture."
Because his theories do not give credit to a Creator, atomism became linked with
atheism. This persisted into the mid-1800s. (In 17th century France you could be
burned at the stake for believing in atoms.)
Plato
lived from 427 BC to 347 BC
Plato in a Small Nutshell
• The world cannot not be known through the senses (world view
presented by the senses are like shadows on a cave wall)
• The philosopher, through pure thought, can see through surface
appearances to the ideal forms underneath.
• The heavens, for example, are perfect and, therefore, move in
uniform, circular motion because a circle is the perfect form.
• Question for students: If the heavens move uniformly in perfect
circles, then why do planets appear to make loops in the sky and
speed up, then slow down?
Ancient Greek Astronomers (3)
• Eudoxus (409 – 356 B.C.):
Model of 27 nested spheres
• Aristotle (384 – 322 B.C.),
major authority of philosophy
until the late middle ages:
Universe can be divided in 2
parts:
1. Imperfect, changeable Earth,
2. Perfect Heavens (described
by spheres)
• He expanded Eudoxus’ Model to use 55 spheres.
Axis of sun
sphere
Sphere of the stars
Earth
Sphere of the Sun
Axis of stellar sphere
Eudoxus’ Cosmos (simplified)
Saturn
Moon
Venus
Earth
Mars
Mercury
Sun
Jupiter
Sphere of Fixed Stars
Aristotle’s Cosmos (simplified)
Aristotle’s Physics
• What is the world made of?
Earth, Water, Air, and Fire
• How do things move?
• Natural Motion (towards the Earth)
• Violent Motion (requires a force)
• The Heavens are different from the Earth
• Made of fifth substance (Quintessence)
• Experience only circular motion
• Other than repetitive circular motion, heavens experience no change
• The Earth is Round
• The moon revolves around Earth, giving us lunar phases
N
A
B
B
S
Aristotle’s argument (2): Observer at A never sees star B. However, if he travels south to position
B, star B becomes visible. Therefore, the earth’s surface must be curved.
Aristotle’s argument (1): Shadow cast by earth on the
moon during an eclipse is always curved. The only
geometric shape which always casts a circular shadow
is a sphere
Aristarchus of Samos
c. 310 – 230 BC
• Proposed a heliocentric system
• Distance and size of the moon
• Distance and size of the sun
• Geometry of eclipses
Aristarchus of Samos
Proposed a heliocentric system -
His belief in a heliocentric system was not popular.
Many argued against it. Arguments included:
• If Earth is moving, why don’t we feel it?
• If Earth is moving, why don’t we leave the moon
behind?
• If Earth is moving around the sun, why don’t we see
stellar parallax?
Parallax
Aristarchus of Samos
If Earth is moving around the sun, why don’t we see stellar parallax?
Philosophers who did not believe in a heliocentric system argued that no
stellar parallax meant Earth didn’t move and Aristarchus was wrong.
Now we know Earth does move, so why don’t we see stellar parallax?
Try putting your finger in front of your nose and looking at it with one eye
and then the other. Now move your finger farther from your face and try
again. Move it farther still, and try again. What do you see?
We don’t see stellar parallax because the stars are so far from us. The
Greeks did not consider this answer as their version of the universe was
smaller than our solar system.
We know can measure stellar parallax for a handful of stars that are close
to us.
Moon at first
quarter
Right angle
Earth
Angular separation between
sun and moon when moon
is at first quarter
Sun
Relative Distances of Sun and Moon
Method of Aristarchus
Moon at first
quarter
Right angle
To Sun
Earth
Angular separation between sun and moon
when moon is at first quarter is so close to
90 (89.5) that it could not be reliably
measured in ancient times
Problem with Aristarchus’ Method
• Circumference of Earth
• Tilt of Earth
Eratosthenes
Lived from 276 B.C. to 195 B.C.
How big is Earth?
• Start with a circle.
• He heard tell of a town named Syene,
where on a particular day of the year at
noon there were no shadows on the water
To Sun
in the water well.
To Sun
Alexandria
• The Sun was overhead.
Syene
• He was in Alexandria.
• The sun was not overhead
for him, but he could
measure the angle between
overhead and the Sun.
How big is Earth?
• He calculated the angle using shadows. It was
approximately 7°.
• We have 2 parallel lines, bisected by a third line
• What can we say about
To Sun
this angle?
To Sun
Alexandria
• It is the same! 7°!
7°
?
7°
7°
Syene
7°
How big is Earth?
• Now we have a 7° “pie piece” of Earth.
• A circle has 360°.
• We can keep adding “pie pieces” until we get to
360°.
To Sun
• Then you can calculate
To Sun
Alexandria
the circumference. If you
Syene
know the distance
between the two towns,
you just keep adding that
distance all the way
around the circle.
7°
D
7°
360°
How big is Earth?
• Did he get the right answer?
• That depends on how well he measured the
distance between towns (without an odometer
or a GPS).
To Sun
• He measured the distance
To Sun
Alexandria
between Syene and
Syene
Alexandria as ~ 5,000 stadia
• We think he was off by a bit.
Depending on the length of
a stadia, he was off by 314%. Best estimate yet!
7°
D
7°
Tilt of Earth
• measured difference
between noontime elevation
of Sun in winter and
summer
• deduced that Earth's
equator is tilted by 23.5
degrees
• difference in height of Sun
at different times gives
latitude
Tilt of Earth
• We now know that the tilt
(obliquity) varies over a 400,000
year cycle.
• It ranges from 22.1 to 24.5.
Hipparchus of Rhodes
lived from 190 BC to 120 BC
Achievements of Hipparchus
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•
•
•
•
Trigonometry
1st Large Star Catalog (about 3000 stars)
Invented latitude and longitude
Discovered Precession
Measured the length of a year to 6
minutes
• Used Eccentrics to explain retrograde
motion (moved Earth off exact center)
Precession (1)
At left, gravity is pulling on a slanted top. =>
Wobbling around the vertical.
The Sun’s gravity is doing the same to Earth.
The resulting “wobbling” of Earth’s axis of rotation around the
vertical w.r.t. the Ecliptic takes about 26,000 years and is
called precession.
Precession
As a result of precession, the celestial
north pole follows a circular pattern on
the sky, once every 26,000 years.
Precession is caused by the
gravitational effects of the sun and
moon.
The pole will be closest to Polaris
~ A.D. 2100.
There is nothing peculiar about
Polaris at all (neither particularly
bright nor nearby etc.)
~ 12,000 years from now, the
celestial north pole will be close
to Vega in the constellation Lyra.
North and South Precession
Later refinements (2nd century B.C.)
• Hipparchus: Placing the Earth away from the centers of the
“perfect spheres”
• Ptolemy: Further refinements, including epicycles
Claudius Ptolemy
lived from 85 to 165
Ptolemy – The Almagest
• Ptolemy's greatest work was the Almagest. It was a combination
textbook, encyclopedia, and astronomical almanac.
• It was a remarkable piece of work, despite the errors. The Greek title
was "Great Syntaxis" or "Great Compilation" but the European title
comes from the Arabic Al Majisti, the same root word as majestic and
majesty, essentially "The Greatest."
• It was essentially a collection and compilation of data, calculations,
methods of observations and calculation, and tables of planetary
locations. Basically, a compendium of six hundred years of Greek
astronomy as well as new results of his own work on planetary motion.
• It also contained an updated star catalog, with several hundred new
stars discovered and located by himself and others since Hipparchus's
time nearly two hundred and fifty years before.
• The book defined the basis of mathematical astronomy and remained
the best and simplest until Copernicus described his heliocentric
methods in the sixteenth century
Deferent
Equant
Earth
planet
For this scheme to work,
Earth has to be offset from the
center
Ptolemy’s System
Epicycle
Here are the retrograde loops as formed
by a single epicycle on the deferent.
Notice how the motion creates a single
and symmetrical set of loops.
Epicycles
Introduced to explain
retrograde (westward)
motion of planets
The Ptolemaic system was considered
the “standard model” of the Universe
until the Copernican Revolution.
Distance to the Moon
• Ptolemy also calculated the distance to the
moon.
R
60 x Radius of Earth
Not to scale.
Medieval Times
Time period in Western Europe from the fall of
Rome (476) to around 1500
Characteristics:
Europe divided into a multitude of warring
principalities
Relatively little intellectual activity due to
turbulent social conditions
Learning (mostly religious) carried on in
Monasteries
Medieval Times
“900 years without a bath” Monty Python
The Dark Ages
Other Parts of the world were flourishing
Islamic world (Spain to India)
China
Mesoamerica (Maya, Inca)
Islamic achievements during the medieval period
Mathematics
• Arabic numerals
• algebra
• trigonometry
• Optics (Al-Hazen of Basara invents the camera obscura)
• Astronomy
• commentaries and improvements on Ptolemy
• more accurate almanacs
• development of the astrolabe
• Preservation of ancient texts
Medieval Times
Medieval European cosmology was always from a
Christian perspective. Realistic physical and
mathematical models of the universe were not of
great interest to most Christian scholars (virtually
all of whom were priests or monks).
In the later Middle Ages (after 1200) Aristotle’s
cosmos was cast in a Christian form.
The Renaissance
(1400 - 1600)
• By 1500 Western Europe was experiencing a Renaissance (“rebirth”) of
scholarship.
• Problems with Ptolemy were viewed with greater seriousness
than in previous centuries.
• Discovery of lands unknown to the Greeks cast doubt on the “wisdom
of the ancients”.
• Time was ripe for fresh thinking about celestial motions
•Nicolas Copernicus
(Revived heliocentric theory)
•Tycho Brahe
(Last great naked eye observer)
•Johannes Kepler
(Elliptical orbits, three laws of motion)
•Galileo Galilei
(Telescopic observations, dynamics of motion)
• Polish, born near Torun
• Earned his living as a cathedral Cannon
(un- ordained church official)
• Proposed a heliocentric system with the
Earth as a planet rotating and moving
along a circular orbit around the central
Sun just like all the other planets.
• Published brief versions of the model
during his lifetime, but waited until he was
near death to publish “On the Revolutions
of the Heavenly Spheres”, the complete
Nicholas Copernicus theory
(1473 – 1543)
Mars
Sun
Mercury
Earth
Venus
Saturn
Jupiter
Copernicus’ Heliocentric System
Copernicus’ new (and correct) explanation
for retrograde motion of the planets
Retrograde
(westward)
motion of a
planet occurs
when the
Earth passes
the planet.
This made Ptolemy’s epicycles unnecessary.
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
Retrograde Motion in the Copernican System
Background stars
Earth
Mars
Apparent path of Mars
The Heliocentric Solar System of Copernicus
• Highlights of Copernicus’ system
• Earth is a planet
• Day and night are due to the rotation of the Earth
• The year is due to the revolution of the Earth around the Sun
• The Moon is the only celestial body which orbits the Earth
• Explained retrograde motion in an elegant manner
• Explained why Venus and Mercury are always near the Sun
• Provided a straightforward way of determining the scale of the
solar system
• Problems with Copernicus’ system
• Predictions of planetary positions no better than Ptolemy
• If the Earth is moving why don’t we feel it?
• If the Earth is a planet, the other planets must be like Earth. Are they?
• Why don’t the stars appear to shift as the Earth changes position
• This system is physically impossible according to Aristotle’s physics.
• Danish, born in Skaane (now in Sweden)
• A nobleman who established an
observatory on an island near Copenhagen
• Devised new and improved existing
instruments which were used to produce
the most accurate star maps ever made
• Not a Copernican, but demonstrated that,
contrary to Aristotle, the heavens are
changeable (comets are celestial and new
stars, “novae,” appear)
Tycho Brahe
(1546 – 1601)
• These data were invaluable to Johannes
Kepler who used them to formulate his
orbital model
Tycho Brahe (1546 – 1601)
• High precision observations of the
positions of stars and planets
• Measurement of the nightly motion of a “new
star” (a supernova) showed no parallax
• Evidence against Aristotelian belief of
“perfect”, unchangeable heavens
Tycho Brahe’s Legacy
New World model
• Still geocentric (Earth in the center of
the sphere of stars)
• Sun and Moon orbit Earth;
Planets orbit the sun.
Tycho’s Compromise System
• German, born near Stuttgart
• Lived in near poverty most of his life,
usually earning a living as a teacher of
mathematics
• Became convinced of the truth of the
Copernican model and was determined to
make its predictions more accurate
• Went to work for Tycho
• Discovered that if Copernicus’ circular
orbits were replaced by ellipses, then
predicted positions of the planets were
more accurate than Ptolemy.
Johannes Kepler
(1571 - 1630)
• His work is summarized in his Three Laws
of Motion
Kepler’s Laws of Planetary Motion
1. The orbits of the planets are ellipses with the
sun at one focus.
c
Semimajor
axis
Eccentricity e = c/a
Eccentricities of Ellipses
1)
2)
e = 0.02
3)
e = 0.1
e = 0.2
5)
4)
e = 0.4
e = 0.6
Eccentricities of Planetary Orbits
Orbits of planets are virtually
indistinguishable from circles:
Earth: e = 0.0167
varies over period of ~ 100,000 years,
from e=0.0005 to e=0.0607
Most extreme example: dwarf
planet Pluto: e = 0.248
Planetary Orbits (2)
2. A line from a planet to the sun sweeps
over equal areas in equal intervals of time.
Planetary Orbits (3)
3. A planet’s orbital period (P) squared is
proportional to its average distance from the
sun (a) cubed:
Py2 = aAU3
(Py = period in years;
aAU = distance in AU)
• Italian, born in Pisa
• Studied medicine, but excelled in
mathematics and physics
• Taught at Pisa, Padua and Florence
• First physicist in the modern sense.
Fundamental work on moving bodies
• Heard about the telescope invented in
Holland and built an improved version
• Used the telescope to discover craters on
the moon, spots on the sun, phases of
Venus and the moons of Jupiter
Galileo Galilei
(1564 - 1642)
• Became a convinced Copernican and
wrote “Dialogue Concerning the Two Chief
World Systems”, a treatise expounding his
views.
• Condemned by the Church for teaching
Copernicanism a proven fact
Surface of the Moon
Showed that the moon is not a
smooth sphere; appears to be a
“landscape”, thus it is a “world”
Moons of Jupiter
A “miniature solar system”; bodies
can orbit something other than
Earth (contrary to Aristotle)
Phases of Venus
Venus exhibits all phases, just like
the moon; thus, Venus must orbit
the sun, and its orbit must be closer
to the sun than the Earth’s.
Mars and Saturn
Planets show disks something like
the moon, implying they are also
“worlds”. Saturn’s puzzling shape
implies that we don’t everything in
the universe.
Sunspots
Showed that the sun’s surface is not
“perfect”, a position advocated by
Aristotle and widely accepted.
Milky Way
The telescope revealed many more
stars not visible to the naked eye.
Implied a three dimensional
universal.
Major Discoveries of Galileo
• Moons of Jupiter
(4 Galilean moons)
(What he really saw)
• Rings of Saturn
(What he really saw)
Major Discoveries of Galileo (2)
• Surface structures on the moon; first estimates
of the height of mountains on the moon
Major Discoveries of Galileo (3)
• Sun spots (proving that the
sun is not perfect!)
Major Discoveries of Galileo (4)
• Phases of Venus (including “full Venus”),
proving that Venus orbits the sun, not the Earth!
Phases of Venus
Galileo's finger is on display at the Museo di
Storia del Scienza in Florence, Italy.
The finger was detached from Galileo's body by
Anton Francesco Gori (Florence, 1691-1757,
literate and antiquary) on 12 March 1737 when
Galileo's remains were transferred from a small
closet next to the chapel of Saints Cosmas and
Damian to the main body of the church of Santa
Croce where a mausoleum had been built by
Vincenzo Viviani.
This is a normal sized finger in a small cup.
Galileo may have approved…. It is his middle finger!
Historical Overview
Issues Raised by the Copernican System
• Why do planets move in elliptical orbits?
• If the earth is moving, why don’t we feel it?
• What keeps the earth, moon and planets
moving?
• Why don’t we see parallax as the earth
moves around the sun?
Isaac Newton (1642 – 1727)
Newton Summarized
Law of Universal Gravitation
F = G(m1 x m2 )/r2
Three Laws of Motion
1.
A body stays at rest or moving uniformly until
acted upon by an external force
2.
The force acting on a body is proportional to
its mass and its change in velocity
(acceleration)
F=mxa
3.
For every action there is an equal and and
opposite reaction
The Universal Law of Gravity
• Any two bodies are attracting each
other through gravitation, with a force
proportional to the product of their
masses and inversely proportional to
the square of their distance:
F=-G
Mm
r2
(G is the Universal constant of gravity.)
First Law (Law of Inertia)
Second Law (F=ma)
Third Law (action – reaction)
NASA photo
Third Law: Action - Reaction
The first law of motion and the universal law of gravity explains
why the Earth orbits the Sun
V
F=G(Ms x Me)/r2
The only force acting on the Earth is the mutual gravitational attraction
of the Sun. Without this force, Earth would continue in a straight line at
velocity V. Instead, it is pulled in a path around the Sun. If an external
force somehow brought V to zero, Earth would collide with the Sun.
The Scientific Revolution
Generally, the period between the publication of Copernicus’
On the Revolutions of the Heavenly Orbs (1543) and the
publication of Newton’s Mathematical Principles of Natural
Philosophy (1687)
During this period the scholarly outlook changed from a static
Earth in a geocentric universe to a dynamic heliocentric solar
system with a moving Earth as one of the planets.
The success of Newton’s laws in explaining this new universe
with mathematical precision encouraged scholars to believe
that all natural phenomena could be explained following the
scientific method (experiment and theory) rather than by
deductive logic based on authority.
Historical Overview
William Herschel 1738 - 1822
William Herschel’ Legacy
• Discovery of Uranus
• “Father” of Stellar Astronomy
• First Serious Use of Reflecting Telescope
• First Model of the Universe Based
on Systematic Observation (Disk of Stars)
• Binary Stars (physically connected double stars)
• shows Newton’s laws are universal
• shows stars have different luminosities
• Extensive Catalog of Nebulae
• Discovery of “Invisible” (Infrared) Radiation
Herschel’s Conclusion from Star Counts
Stars appear to
be concentrated
here (Milky Way)
Photo of Milky Way
Fewer stars with
some nearby
bright ones away
from Milky Way
Implied Structure of Stellar System
Fewer stars seen
Apparent Celestial Sphere
More stars seen
Sun
More stars seen
Fewer stars seen
Herschel’s Actual Plot from Data
Einstein and Relativity
Einstein (1879 – 1955) noticed
that Newton’s laws of motion are
only correct in the limit of low
velocities, much less than the
speed of light.
Theory of Special Relativity
(1905)
Photoelectric Effect (1905)
Nobel Prize in 1921.
 Theory
(1916)
of General Relativity
Two Postulates Leading to Special
Relativity (1)
1. Observers can
never detect their
uniform motion,
except relative to
other objects.
This is equivalent to:
The laws of physics are the same for all
observers, no matter what their motion, as
long as they are not accelerated.
Two Postulates Leading to Special
Relativity (2)
2. The velocity of
light, c, is
constant and
will be the
same for all
observers,
independent of
their motion
relative to the
light source.
Basics of Special Relativity
The two postulates of special relativity
have some amazing consequences.
• Time dilation: The faster
something moves, the slower time
goes for it.
• Length contraction: Length scales
on a rapidly moving object appear
shortened
• Relativistic aberration: Distortion of angles
• The energy of a body at
rest is not 0. Instead, we
find
E0 = m c2
General Relativity
A new description of gravity
Postulate:
Equivalence Principle:
“Observers can not
distinguish locally
between inertial forces
due to acceleration and
uniform gravitational
forces due to the
presence of massive
bodies.”
Einstein’s Theories of Relativity
General relativity
It is impossible
to tell, from
within a closed
system, whether
one is in a
gravitational
field, or
accelerating:
Einstein’s Theories of Relativity
Matter tends to warp
spacetime, and in
doing so redefines
straight lines (the
path a light beam
would take):
A black hole occurs
when the
“indentation”
caused by the mass
of the hole becomes
infinitely deep.
Thought Experiment (Conclusion)
This bending of light by the gravitation of massive
bodies has indeed been observed:
During total solar eclipses:
The positions of stars apparently close to the sun are
shifted away from the position of the sun.
 New description of gravity as
curvature of space-time!
Photoelectric effect
Photoelectric effect can be understood only if
light behaves like particles
The Structure of the Cosmos
600 BC (Thales)
1600 (Kepler)
1920 (Shapley)
300 BC (Aristotle)
1600 (Digges)
1930 (Hubble)
1543 AD (Copernicus)
1800 (Herschel)
2000 (Geller)