Transcript Gökküre - itü | fizik mühendisliği

History of Astronomy
• Enka Schools, April 24th, 2007
• By Yavuz Ekşi (İTÜ)
• http://www.fizik.itu.edu.tr/eksiy/
Briefly…
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Celestial Sphere=Gökküre=Felek
Planets and Their Retrogade Motion
Aristotelian World View
The Copernican Revolution-The
Earth is a Celestial Object!
Diurnal Motion
Apparent
Daily Motion
of Stars
Around
the Earth
Diurnal
Motion
Stars move East
to West as the
Earth rotates
West to East.
They cover 15
degrees per hour
which amounts to
360 degrees per
day!
Ancient World View
• Ancient people believed
that the Earth was at the
center of the Universe,
motionless and nonrotating.
• For the ancient people
the circular trajectories
of the stars were not just
an apparent motion.
• According to them the
stars were indeed
rotating around the
Earth.
Contellations
• Ancient people
identified patterns
of stars called
constellations.
• This allows one to
find stars easy.
Constellations
Constellation=takımyıldız
The stars in the constellations are not physically close but
their projections onto the celestial sphere appear to be close.
Constellations help to locate objects on the sky.
Globular Cluster
These are stars physically
close to each other.
Constellations preserve their
form during diurnal motion
Celestial Sphere
• The stars are not rotating by their
own but they are fixed onto a sphere
and the diurnal rotation of the stars
is due to the rotation of this sphere.
• This sphere is called the celestial
sphere.
• Celestial Sphere
is still a useful
concept because
we only see the
projections of
celestial objects
on such a
fictitious sphere.
• Measuring the
distances is a hard
problem of
astronomy.
Celestial Sphere=Gökküre=Felek (Çoğ:Eflak)
Seven Objects not Fixed to
the Celestial Sphere
• For the ancient people the celestial
sphere was a real object!
• All stars were fixed onto this sphere
but there were 7 objects moving
independent of the celestial sphere.
• These are the 5 planets that can be
identified by the naked eye (Mercury,
Venus, Mars, Jupiter, Saturn), the
Moon, and the Sun.
Retrogade Motion of Mars
Retrogade
motion of
Mars
according to
the
heliocentric
model
Retrogade
motion of Mars
according to the
heliocentric
model
http://faculty.fullerton.edu/cmcconnell/Planets.html
Modern Science was born out of
the human desire to explain the
retrogade motion of the planets.
Planets
• Planetes means wanderers in Greek.
• Planet = Gezegen = Seyyare
• Notice they all carry the same meaning
referencing their apparent wandering with
respect to the “fixed” stars.
• For the ancient people planets were gods
and they gave their name to each day of
the week.
Days of the Week
Saturday
Saturn=dies saturni
Sunday
Sun=dies solis
Monday
Moon=dies lunae
Tuesday
TiwMars=dies martis
Wednesday
OdinMercury=dies Mercurii
Thursday
Tor  Jupiter=dies jovis
Friday
Frie  Venus=dies veneris
http://en.wikipedia.org/wiki/Days_of_the_week
Astronomical Names for the Days of the Week, Falk, M.., 1999, J. of the Royal Astron. Soc. of Canada, Vol. 93, p.122
Aristoteles (M.Ö.384-322)
• The Earth is a sphere at
the center of a spherical
universe
• The Moon, Mercury, Venus,
the Sun, Mars, Jupiter,
Saturn and fixed stars each
rotate around their own
spheres.
• These spheres are made of
crystal (so that they are
not seen)
The 7
Spheres
Above the
Earth
Below the
Celestial
Sphere
Felek
• Feleğin tekerine çomak sokmak
• Felekten bir gün çalmak
• Feleğin çemberinden (çeperinden?)
geçmek.
Aristoteles...
• Dominated the philosophy all throughout
the medieval ages.
• The research at that time simply meant
finding out what Aristoteles said about
that research topic. No experiment, no
questioning.
Aristotelian Chemistry
Aristoteles: Objects on Earth and
Celestial Objects are composed of
Different Elements
• Objects on Earth (everything below the
sphere of the Moon) are a mixture of 4
elements: Earth, Water, Air and Fire. Such
objects are subject to change, decay
and/or death and are defected.
• Celestial Objects are made from a fifth
element (Ether). Such objects are
defectless/perfect, and eternal. They are
not subject to any change.
Aristoteles: Objects on the Earth and the
Celestial Objects Obey Different Laws
• Each element has a natural place determining its natural
motion: Earth belongs to the Earth. The natural place of Water is arround earth.
Natural place of Air is above Earth & Water. And Fire is to be above the Air. A
stone falls down because it belongs to the Earth. Fire tends to rise up because it
wants to reach the greatest fire (the Sun), the bubbles in water rise up because air
is to be above water, etc.
• Apart from the natural motions there are forced
(violent) motions. One has to apply force in order to
keep objects in motion: The card stops when the horse
stops.
• Heavier objects fall more rapidly than the lighter
objects.
• Celestial objects eternally follow circular trajectories.
They do not change their speed during this motion.
• Each celestial object rotates around the Earth.
Comets According to Aristoteles
• The celestial objects
are eternal and the
sky is not subject to
change.
• Hence comets must
be inside the sphere
of the Moon, i.e.
they are
atmospheric events.
Aristarchus of Samos
• Many canturies before
Aristoteles, he
suggested the helicentric
universe model.
• His heliocentric model
was not commonly
accepted at that time
because...
(310-230 BC)
...parallax can
not be
measure with
naked eye.
The Heliocentric model of
Aristarchus was not generally
accepted because...
• It is hard to accept the stars being so
distant that they do not show any
parallax.
• If the Earth is rotating, it would be
very hard for us to walk on it. We would
be centrifugally expelled.
• Say the Earth is rotating around the
Sun, then how would the Moon be
carried along with us?
Summary: For the Ancient People...
• Objects on the Earth and the Celestial
Objects have different structures.
• Celestial objects are perfect while the
objects on the Earth are defected and are
subject to decay.
• Different laws in the sky and on the Earth.
• The Earth is at the center of the Universe
(obviously!)
• So how could they explain the retrogade
motion of Mars?
Hipparchus & Epicycles
• Retrograde motion of planets
could be explained by a
combination of circular motions;
• the planet moves in a small
circle called an epicycle
• the centre of the epicycle
moves around a larger circle
called the deferent
• If the planet moves around the
epicycle faster than the
epicycle moves around the
deferent, retrograde motion will
occur in some regions of the
orbit
Ptolemy=Batlamyus
(Claudius Ptolemaeus-140 AD)
• Ptolemy expanded upon Aristotles geocentric
model to predict the motion of planets accurately.
• Following Hipparchus, he assumed that planets
moved around circular epicycles. The centres of
the epicycles moves around the Earth in circular
deferents.
• He added a number of refinements to the old
model to obtain better agreement with
observations. In particular, he offset the centre
of the deferent from the centre of the Earth!
Geocentric
model and the
retrogade
motion of Mars
Ptolemaic Model of the
Universe
The Ptolemaic Model
• Ptolemy was able to predict the
motions of the seven celestial objects
to great accuracy by introducing more
and more epicycles.
• Ptolemy’s model had been used nearly
for 1500 years by the western and
eastern astronomers.
Size of the
Earth
Comparable
to the size
of the
Heavens
The rest of the
Universe
was comparable
to the
size of the
Earth.
Nicolaus Copernicus (1473-1543)
• “Who in this most
beautiful of temple
would put his lamp
at a better place
than from where it
can illuminate them
all?. Thus the Sun
sitting as on a
Royal throne, leads
the surrounding
family of stars!”
Tycho Brahe (1546-1601)
• Observed a supernova
explosion (1572).
• He thought this was a
new star.
• Surprised because he
thought the celestial
objects are eternal
and the sky does not
change.
Stella Nova
• The image in
this page is
from Tycho
Brahe's
"Stella
Nova“.
http://www.texts.dnlb.dk/DeNovaStella/Index.html
Tycho Brahe and Comets
• Observed a comet
• Made collaborations with an observer at a
different location to find that the comet
was nearly in the same position with
respect to the background stars for both
observers (i.e. no parallax).
• Concluded that the comet was at least six
times farther away than the Moon.
Tycho Brahe and the Crystal Spheres
• Tycho Brahe also understood that the
comet must have passed through the
spheres.
• So the crystal spheres of Aristoteles
can not be real!
Galileo (1564-1642)
• The Second Scientist
after Gilbert
• A strong refuter of
the Aristotelian world
view.
Galilei Supernova
• In 1604 he observed the SN studied by Kepler.
• He thought this was a new star.
• The new star showed no motion accross the sky
compared with the other stars (i.e. No parallax)
• Gave series of lectures arguing that it must be as
far away from the Earth as the other stars.
• This refutes the Aristotelian notion of an
unchanging celestial sphere.
A Celestial Object Defected?
• Directed his
telescope to the
sky (1609).
• The Moon is not
perfect! It has
craters which
are defects.
Galileo Galilei
• I would rather discover a single fact,
even a small one, than debate the
great issues at length without
discovering anything new at all.
-Galileo Galilei
...Galileo
• Discovered Jupiter’s moons.
• This implies that (independent
of whether the geoentric or
heliocentric model is true) not
every celestial object
rotates around the Earth.
• This also obviates the
argument against the
Copernican sytem that if
the Earth rotated around
the Sun then the Earth and
the Moon would get
separated from one
another.
Galilei observed the Phases of Venus
• Heliocentric Model: All phases should be visible
• Geocentric Model: Only crescent and new phases
would be seen
The phases of Venus according
to the geocentric model
• Venus can only be seen
just after the sun sets.
This means that it must
be very close to the
Sun.
• In order that they
always remain close,
their spheres must be
locked to each other.
• According to this model
Venus can never be in an
opposite position to the
Sun and so show the
phases that Dalileo
observed.
Galilei and the Milky Way
As seen with
the telescope
Milky Way is a
myriad of
individual stars.
The Sun also is not Perfect
(Galilei 1613)
Aristotelian Response
• Aristotelians refused to accept that
what was seen through the telescope
was real.
• Galileo himself tested the possibility
by observing hundreds of objects to
see if the instrument does anything
except magnify.
Newton (1687)
• Gravitational attraction is between all bodies.
• The force that keeps the Moon in orbit is the
same force that causes the apple to fall
down.
• Objects on the Earth and the objects in the
sky obey the same laws.
M m
F  G 2
r
G  6.67 10
11
3
2
m /(s kg)
New Mechanics

Aristotelian view: forces cause velocity
(force necessary to maintain uniform motion).

Newtonian view: forces cause acceleration
(force necessary to change motion)
Bessel (1838)
• Successfully measured the
parallax of the star 61 Cygni.
• This was considered as the
conclusive evidence that the
Earth was in motion.
Spectroscopy
• Each element has its
own signature.
• The light from the
stars carry
information about
the elements in the
stars and planets.
• Scientists can
understand which
elements make up
the celestial objects
by looking at the
spectra.
Objects on the Earth and
Celestial Objects are made of
same kind of elements
• Spectroscopy discovered in the 19th century
• Using spectroscopy astronomers understood
that stars are made of mainly hydrogen and
some other elements like Carbon and Oxygen
that also make up the Earth.
• This was the final stroke to the Aristotelian
world view.
A century of Astronomy