Transcript The Beginnings of Modern Astronomy

The Beginnings of
Modern Astronomy
Copernicus to Kepler
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Trouble in Vatican City
• The calendar was still a mess
• Three ways to describe a year:
– Julian calendar year = 365.25 days
• Civil time
– Sidereal year = 365.256366 days
– Tropical year = 365.242199 days
• Seasonal time
The Problem
• Because the Earth precesses the
Tropical year is 11 min 14 sec shorter
than civil (Julian) calendar year
• Every 130 years the calendar is off one
day
• Eventually the calendar was 10 days
out of sync with the seasons
• Lunar calendar off by 4 days
Why it Mattered
• Easter and other religious holidays are based on
celestial motions
– First Sunday after the first full moon after the Vernal Equinox
• But the Vernal Equinox was drifting
• Without calendrical reform Easter would eventually be in
December!
• Other days were important for holidays, indulgences
– Holidays were an enticement for lay parishioners as a
reaction to the Reformation
– A partial indulgence is granted to Christian faithful who, on
day of the liturgical feast of any saint, recites in that Saint's
honor a prayer
• Some historians suggest that this
calendrical need inadvertently kick-started
the scientific revolution, as well as fueled
the cultural rebirth known as the
Renaissance
• The Church certainly did not see where
this reform would lead
– Correcting the positions of planets was seen
as independent of Catholic cosmology
• Gregorian Calendar fix
– Oct 5 – 14, 1582 never existed!
– New leap year rules established
The Big Four
•
•
•
•
Nicholas Copernicus
Tycho Brahe
Johannes Kepler
Galileo Galilei
– Featured in another slideshow
• Nicholas Copernicus
•
“Swedish DNA expert Marie
Allen speaks at a news
conference to announce the
identification of remains
believed to belong to Nicolaus
Copernicus, in Warsaw, Poland,
on Thursday, Nov. 20, 2008.
Researchers believe they have
identified the remains of
Nicolaus Copernicus by
comparing DNA from a skeleton
they have found with that of hair
retrieved from one of the 16thcentury astronomer's books.*”
*San Francisco Gate, 11/20/2008
• B. 1473, Torun, Prussia (present-day Poland)
• Well educated:
– 1491 University of Kracow, studied church law
– 1496 University of Bologna, studied Greek, philosophy,
astronomy, medicine
– 1501 University of Padua; studied law and medicine
• 1503 returned from Italy to Torun; served as
physician, cleric, scholar
• 1514 circulated Commentariolus (Little Commentary)
among his friends
– 40-page non-mathematical treatise extolling heliocentrism
– Possible fix for the calendar
The Little Commentary (excerpt)
The planetary theories of Ptolemy and most other astronomers,
although consistent with the numerical data, seemed likewise to
present no small difficulty. For these theories were not
adequate unless certain equants were also conceived ... a
system of this sort seemed neither sufficiently absolute, nor
sufficiently pleasing to the mind. I considered whether there
could be found a more reasonable arrangement of circles....
Let no one suppose that I have gratuitously asserted, with the
Pythagoreans, the motion of the earth; strong proof will be found
in my exposition of the circles.
For the principal arguments by which the natural philosophers
attempt to establish the immobility of the earth rest for the most
part on the appearances; it is particularly such arguments that
collapse here, since I treat the earth's immobility as due to an
appearance.
His Assumptions:
•
Heliocentrism
–
–
Not the first: Aristarchus, for one
Used existing tables,
•
–
•
•
•
Did no observations himself
Tables were no better that those Ptolemy used
Rorbit small compared to distance to stars: parallax,
relative motion
Apparent motion of heavens due to Earth motion
Retrograde motion a consequence of the other
assumptions
95 Theses
• 1517
• Schlosskirche in
Wittenberg, the church
where the theses were
nailed
• No fan of heliocentrism,
but poorer and less
vindictive than Church in
Rome
– Luther actually protested
heliocentrism in 1539!
Georg Joachim Rheticus (1514-1575)
• A Copernicus protégé
• 1541: encouraged him to prepare his treatise
The Revolutions of the Heavenly Bodies for
publication
– Copernicus had essentially finished it in 1532 but
resisted publishing: “[it would] expose himself [to
scorn] on account of the novelty and
incomprehensibility of [the] theses”
Cardinal Nikolaus von Schönberg,
Archbishop of Capua, to Copernicus in
1536
• “Some years ago word reached me concerning your
proficiency, of which everybody constantly spoke. At that
time I began to have a very high regard for you... For I had
learned that you had not merely mastered the discoveries
of the ancient astronomers uncommonly well but had also
formulated a new cosmology. In it you maintain that the
earth moves; that the sun occupies the lowest, and thus
the central, place in the universe... Therefore with the
utmost earnestness I entreat you, most learned sir, unless
I inconvenience you, to communicate this discovery of
yours to scholars, and at the earliest possible moment to
send me your writings on the sphere of the universe
together with the tables and whatever else you have that
is relevant to this subject …
• 1542: manuscript taken to Nuremburg
– Rheticus is too busy with his teaching responsibilities
– Publication task taken over by Andreas Osiander
• 1542: Copernicus suffers a stroke
• The Revolutions of the Heavenly Bodies finally
published in 1543
– Copernicus dies shortly afterward
• Some historians suggest that, since his theories were
heretical, publication was put late in his life lest the
Inquisition investigated
• Other historians deny this, saying the Church was
always behind his work
– Copernicus did include a letter to POPE PAUL III in his
Revolutions.
Preface
•
•
Osiander, a cleric, was very offended
by the book, so he wrote a huge
disclaimer as a preface that
Copernicus didn't approve
The shock of reading it may have
been the last straw for Copernicus!
“There have already been widespread reports about the
novel hypotheses of this work, which declares that
the earth moves whereas the sun is at rest in the
center of the universe. Hence certain scholars, I have
no doubt, are deeply offended and believe that the
liberal arts, which were established long ago on a
sound basis, should not be thrown into confusion…
For it is the duty of an astronomer to compose the
history of the celestial motions through careful and
expert study. Then he must conceive and devise the
causes of these motions or hypotheses about them.
Since he cannot in any way attain to the true causes,
he will adopt whatever suppositions enable the
motions to be computed correctly from the principles
of geometry for the future as well as for the past...”
my italics
Results:
• The Revolutions of the Heavenly Bodies didn’t
actually fix the calendar
– Some aspects made it worse
• He insisted on circular orbits, constant speed
• Didn’t actually completely do away with epicycles but
eliminated the equant
• Did explain retrograde motion
– And why Mercury and Venus are always near the Sun in the
sky but Mars, Jupiter, and Saturn are not
– Ptolemy’s system did not explain this
• Gave very good planetary distances
Distances of Planets from Sun in Earth Radii, (and
Astronomical Units)
Ptolemy
Copernicus
Mercury
100
430 (.4 AU)
Venus
600
820 (.75 AU)
Earth
1,200
1,100 (1 AU)
Mars
5,000
1,700 (1.5 AU)
Jupiter
11,500
6,000 (5.5 AU)
Saturn
17,000
10,500 (9.5 AU)
Stars
20,000
too far to measure
Disadvantages
• Still no sensation of motion
• Fixed stars show no signs of parallax shift
– Copernicus therefore could not calculate their
distance
• Not really simpler
• Violates principle of economy; why is there
so much empty space between Saturn and
the fixed stars?
• No explanation for natural motions of
terrestrial elements; why do things fall?
Still, a Turning Point
• Just as Columbus’ “discovery” of the
New World was a turning point:
– People knew of North America before
Columbus; Astronomers had seen the
heliocentric model before
• But Copernicus’ book was the tipping
point for the Sun-centered theory
Occam’s Razor
• 14th-century English logician and Franciscan friar William
of Ockham
• The Razor: the explanation of any phenomenon should
make as few assumptions as possible, eliminating those
that make no difference in the predictions of the theory
• In Latin: lex parsimoniae ("law of parsimony" or "law of
succinctness"): "entia non sunt multiplicanda praeter
necessitatem", or "entities should not be multiplied beyond
necessity“
• Heliocentrism is geometrically simpler than geocentrism
• Some acceptance, some rejection of the
Copernican theory…
Aristotle Never Dies
• Most people then still subscribed to Aristotle’s
Physics
– Especially the Church, since it placed Earth in the
center of the cosmos with Heaven above and Hell
below
• Universities continued to teach geocentrism
• Even today, most people have an Aristotelian
sense of motion
– Does the Sun really rise?
– Why don’t we feel the motion of us turning, or
whizzing around the Sun?
No one in his sense, or imbued with the slightest knowledge of
physics, will ever think that the earth, heavy and unwieldy from
its own weight and mass, staggers up and down around its own
center and that of the sun; for at the slightest jar of the earth, we
would see cities and fortresses, towns and mountains thrown
down....
For if the earth were to be moved, neither an arrow shot straight up,
nor a stone dropped from the top of a tower would fall
perpendicularly, but either ahead or behind....
Lastly, all things on finding places suitable to their natures, remain
there, as Aristotle writes. Since therefore the earth has been
allotted a place fitting its nature, it cannot be whirled around by
other motion than its own.
Theater of Universal Nature (1597)
Jean Bodin (1520-1596)
my italics
The Week, or Creation of the World
(1578)
by Guillaume du Bartas (1544-1590)
…Arm'd with these Reasons, 'twere superfluous
T'assail the Reasons of Copernicus;
Who to salve better of the Stars th'appearance
Unto the Earth a three-fold motion warrants:
Making the Sun the Center of this All,
Moon, Earth, and Water, in one only Ball…
Thomas Digges
(c.1546-1595)
Tycho Brahe
• Born in Denmark 1546 of wealthy
parents, but leaned academic
• Studied at University of
Copenhagen
– Rhetoric and Philosophy
– But always interested in Astronomy
and Astrology
– Read horoscopes
• Lost his nose in a duel over who
was the better mathematician
• 1572 supernova a watershed event
for Brahe
Uraniborg
•
Family close to King
Frederick II of Denmark
–
–
•
Granted him the fiefdom
of Hven (VEEN), 1576
Brahe builds Uraniborg,
the “Heavenly Castle”
observatory with a great
quadrant, metal, accurate
to 1' of arc
This construction
distinguishes Brahe from
earlier astronomers in
that he actually took his
data and didn’t rely on
earlier tables
The Observatory
• Great Hall at
Uraniborg
– Statues of all the
great Astronomers,
including himself
• And his son, who
never studied
Astronomy
• Also had a backup
observatory,
Stjerneborg, Castle
of the Stars
As an Astronomer
•
•
Tycho kept very accurate
records of 777 stars and
planet locations, better than
anyone before due to his
metal quadrant
Comet of 1577
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–
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•
calls for distant
observations to triangulate
for distance
discovers the comet was
far, far away, little parallax
not an atmospheric event
as per Aristotle
Came up with the geoheliocentric or Tychonian
model, partly to account for
the “waste of space”
between Saturn and the
stars
•
1597 leaves Denmark to go to Prague and (crazy)
Rudolf II
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–
–
•
1588: Tycho’s patron king dies; King Christian IV finds
him annoying and arrogant
Rudolf II great patron of science, arts; wanted great
mathematical tables named after him like 13th C. King
Alphonso X
Tycho actually tired of observing
1599 Kepler joins him
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–
–
•
Tycho is envious of the young mathematician
Leary about giving him data
Gives Kepler only Mars position data
1601 dies of ureamia
–
–
Unusual circumstances
Kepler gets the rest of the data
Giordano Bruno
• Not one of the big four
• B. 1548 in Nola, It.
• Studied at the Monastery
of Saint Domenico
where Thomas Aquinas
had lived and taught
• Enthusiastic and frank
student
• 1581: went to Paris and gave lectures
on Philosophy
• Published the Shadow of Ideas
– Ideas are only shadows of truth
– Christianity is entirely irrational, contrary to
philosophy and it disagrees with other
religions
– This did not make him popular!
• Moves to England, actively spreads the
Copernican theories
• Meets with Queen Elizabeth who finds
him wild, radical, and dangerous
• Fails to secure a position so he moves
to Germany, did odd academic jobs
• Writes On Cause, Principle, and Unity
"This entire globe, this star, not being subject to
death, and dissolution and annihilation being
impossible anywhere in Nature, from time to
time renews itself by changing and altering all
its parts. There is no absolute up or down, as
Aristotle taught; no absolute position in
space; but the position of a body is relative to
that of other bodies. Everywhere there is
incessant relative change in position
throughout the universe, and the observer is
always at the center of things."
• He also writes that the stars are just
other Suns with orbiting planets
inhabited by intelligent beings
• This are the previous selection are
extremely forward-thinking
• But also antithetical to the Catholic
Church
• After 14 years wandering northern
Europe he is lured to Venice with the
promise of a home, then turned in to the
Inquisition
• He remained in a papal prison for 7
years, refusing to recant his philosophy
and writings
• Finally brought before the Grand
Inquisitor Cardinal Bellarmine in Rome
• Pope Clement VIII
declared Bruno to be a
heretic; sentence: death
• “Perhaps you, my
judges, pronounce this
sentence (of death by
fire) against me with
greater fear than I
receive it."
• Bruno was executed in
1600
– But his ideas carried
on…
th
17
Century Cosmic Pluralists
Henry More: “Essay Upon
the Infinity of Worlds" (1647)
the frigid spheres that 'bout
them fare;
Which of themselves quite
dead and barren are,
But by the wakening warmth
of kindly dayes,
And the sweet dewie nights,
in due course raise
Long hidden shapes and life,
to their great Maker's praise.
John Milton: “Paradise Lost” (1667)
Her spots thou seest
As clouds, and clouds may rain, and
rain produce
Fruits in her softened soil, for some to
eat
Allotted there; and other Suns, perhaps,
With their attendant Moons, thou wilt
descry,
Communicating male and female light,
Which two great sexes animate the
World,
Stored in each Orb perhaps with some
that live
Johannes Kepler
• B. 1571 at Weil-derStadt, Germany
• Earned a Master’s
degree from
University of
Tubingen, 1591
• Worked as a math
instructor at Gratz
God as the Great Geometer
• While teaching a
lesson on planetary
conjunctions, Kepler
draws a diagram to
illustrate a series of
conjunctions of
Jupiter and Saturn.
• A pattern emerged
that he believed was
a key to the "cosmic
mystery"
Mysterium Cosmigraphicum, 1596
There were three things in particular about which I
persistently sought the reasons why they were such
and not otherwise: the number, the size, and the
motion of the circles.... In the beginning I attacked
the business by numbers, and considered whether
one circle was twice another, or three times, or four
times, or whatever, and how far any one was
separated from another according to Copernicus. I
wasted a great deal of time on that toil, as if at a
game, since no agreement appeared either in the
proportions themselves or in the differences; and I
derived nothing of value from that except that I
engraved deeply on my memory the distances which
were published by Copernicus.... If (thought I) God
allotted motions to the spheres to correspond with
their distances, similarly he made the distances
themselves correspond with something....
His fourth law
Behold, reader, this is my
discovery and the subject
matter of the whole of this
little work. For if anyone
having a slight
acquaintance with
geometry were informed
of this in so many words,
there would immediately
come to his mind the five
regular solids with the
proportion of their
circumscribed spheres
to those inscribed....
This accident was also the
happy ending of my toil.
Addicted to Euclid
• He adhered to the
Copernican view
– Especially the idea of
circular orbits
• Mystical,
numerological
1599: Watershed
• Accepts a position with Tycho in Prague
• Anxious to get all the very accurate data
Tycho has compiled
• But Tycho is jealous, gives Kepler only
data for Mars
• Has to wait less than two years: Tycho
dies, Kepler gets the notebook
Three Laws
•
•
From Tycho’s notebook, Kepler develops
three laws of planetary motion
We list them out of order from his order of
discovery
1. Planets orbit the Sun in ellipses;
2. Planets sweep out equal areas in equal times
3. The square of the orbital period is proportional to
the cube of the mean radius
•
•
Takes him ten years to develop these laws
Aided by the invention of logarithms by
John Napier
Ellipses
• Like an oval, but mathematically precise
– Around 1080 a Muslim astronomer in Toledo, Spain,
named Arzaquen suggested that planetary orbits are
elliptical, but his conjecture was ignored.
• Remember his love of circles?
• “Why should I mince my words? The truth of
Nature, which I had rejected and chased away,
returned by stealth through the backdoor,
disguising itself to be accepted…Ah, what a
foolish bird I have been!”
• Actually, a circle is a kind of ellipse!
• His second discovery
Equal Areas in Equal Times, and
Ellipses
The Mathy One
• The first two laws were completed by
1609, but Kepler was dissatisfied
– Called elliptical orbits a “cartload of
schiesse”
• With the discovery of the third law by
1619, he was ecstatic and wrote in his
book “On the Harmony of the World”
(Harmonice Mundi):
“I saw the dawn 18 months ago; the bright day
three months ago, and several days ago the
brightest sun of a most wonderful vision. Now,
nothing can restrain me. I let myself go in divine
rage. I defy human beings with contempt in this; I
have stolen the golden vessels of the Egyptians
to create from them a sacred place from my God,
far from the borders of Egypt. If you are angry
with me, I shall bear it; the die is cast; I write for
my contemporaries, or it does not matter for the
future. Perhaps, my book will not have readers for
100 years but God himself has waited 6000 years
for someone to gaze upon his creation with
understanding.”
But Why?
• Kepler had no mathematics to explain
why the planets orbited the way they did
– That would have to wait for Newton
• His laws explain nothing about why
things fall to the ground
• He had a belief that gravity was like
magnetism
• He did postulate the idea of inertia
Later in Life
• 1627: published Rudolphine Tables, the first
astronomical tables based on Kepler's new
system of elliptical orbits
– These are the tables that Tycho wanted named
after him
– Frontispiece to follow
Hipparchus
Tycho pointing
To the book
Copernicus
Ptolemy
Hven
To Be A Copernican
• Not only to accept that the Earth orbits the Sun
• The new Physics for this system requires:
–
–
–
–
New instruments
New techniques
New criteria for judging validity
In short, a new way of doing science
• A sea-change from Aristotle
– Abandon natural and violent motion
– Abandon the Earth as center
– Incur the wraith of Rome, as Bruno did
• There will be a profound change in academia but it
will take 200 years to complete
Letter From Johannes Kepler to
Galileo Galilei, Delivered in April
of 1610:
•
“There will certainly be no lack of human pioneers
when we have mastered the art of flight. Who
would have thought that navigation across the vast
ocean is less dangerous and quieter than in the
narrow, threatening gulfs of the Adriatic , or the
Baltic, or the British straits? Let us create vessels
and sails adjusted to the heavenly ether, and there
will be plenty of people unafraid of the empty
wastes. In the meantime, we shall prepare, for the
brave sky travelers, maps of the celestial bodies - I
shall do it for the moon, you, Galileo, for Jupiter.”