the history and philosophy of astronomy lecture 15: enlightenment: kant, herschel. presentation

8/9/2019 The History and Philosophy of Astronomy Lecture 15: Enlightenment: Kant, Herschel. Presentation

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The History and Philosophyof Astronomy

(Lecture 15: Enlightenment:Kant/Herschel)

Instructor: Volker BrommTA: Jarrett Johnson

The University of Texas at Austin

Astronomy 350L

(Fall 2006)


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Timeline: The Enlightenment Period


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Question:

What is Enlightenment???


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Enlightenment Philosophy

Immanuel Kant (1724-1804)

Critique of Pure Reason(1781):

- Big Q: What can we know?

Theory of the Heavens(1755):

- Island Universes (galaxies)


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Question: What is Enlightenment???

Enlightenment is mans emergence from his self-imposedimmaturity. Immaturity is the inability to use onesunderstanding without guidance from another. Thisimmaturity is self-imposed when its cause lies not in theLack of understanding, but in lack of resolve and courageto use it without guidance from another. Sapere aude!

[dare to know] Have courage to use your ownunderstanding! that is the motto of the Enlightenment.

(Kant, 1784)


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Jean-Jacques Rousseau

(1712-1778)

The Social Contract(1762):

- Man is born free but everywhereis in chains

- Purpose of government: to ensurelife, happiness, general welfare

- bad government: social contract isbroken! Change of governmentlegitimate!


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Political Upheaval: American Revolution

Life, liberty, and the pursuit of happiness


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Political Upheaval: French Revolution (1789)

Liberte, egalite, fraternite!


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Economical Upheaval: Industrial Revolution

James Watt:

- Steam Engine (1774)

beginnings of mass-

production (Taylorism)

Adam Smith (1776):

- Wealth of Nations(Bible of Capitalism)- Theory of the invisible

hand


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The Birth of Chemistry

Antoine Lavoisier (1743-94), discoverer of oxygen


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Big Q: Architecture of Stellar System?

Q: How are stars arranged, and are they really fixed?


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Newtons A: Static, infinite Universe!

Stars are fixed; i.e.: they dont move!


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But what about Milky Way band of stars?

Q: How was Milky Way, and other galaxies, discovered?


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But what about nebulous patches of stars?

Many islands of stars !


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Newton: A Static Universe

Q: Is such a Universe possible (is it stable)?


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Can stellar system be stable under gravity?

A: No! Analogue: Balance infinitely many needles

exactly on their tips! An unstable situation!


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A: No, stars would begin to move around randomly!


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Hunting for Stellar Motions

Slow shift in angular positions proper motions

unsuccessful searchinitially

proper motions areexceedingly small

due to large distance

to the stars!


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Hunting for Stellar Motions

proper motion 1/d

d


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Serendipity: Bradleys Discovery of Aberration

Apparent stellar positions are shifted because ofEarths motion around Sun!


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Bradleys Proof for Earths Motion

James Bradley (AstronomerRoyal, 1693-1762)

1728: `Aberration of Light

Incontrovertible prooffor Earths revolution

around Sun

(Copernicus was right!)


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Q: How are Stars distributed in infinite Space?

Stars are in motion, but what is architecture of stellar system?

OR


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Explaining the Milky Way!

Thomas Wright ofDurham (1711-86)

An Original Theory ofthe Universe(1750)

Concept of Milky Wayas a `Galaxy

(distinct system of

countless stars)


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Wright Explains the Milky Way!

Divine Center

Outer Darkness


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Wright Explains the Milky Way!

Very large R

R

a disc-like appearance (like observed band of MW)!


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Immanuel Kant (1724-1804)

Critique of Pure Reason(1781):

- Big Q: What can we know?

Theory of the Heavens(1755):

- Island Universes (galaxies)


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Kant Postulates Disc-like Milky Way!

basically correct picture for our Milky Way!

direct proof:

COBE, 1993(infraredpicture)


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Kants Cosmogony:

Formation of disc-like systems!

Kant-Laplace hypothesis!


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Kants Hierarchy of Worlds

Island Universes

(`galaxies)

Systems of systems

a fractal universe!


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The Fractal Geometry of Nature

Benoit Mandelbrot

Fractal: self-similarity

Th F l G f N


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The Fractal Geometry of Nature

E li ht t Phil h


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Pierre-Simon de Laplace

(1749-1827)

Exposition de System du Monde(1796)

Laplace Demon:

- a being endowed with unlimitedcapability to compute

- would be able to predict everythingin past, present, and future

- a completely deterministic universe!

E li ht t A t


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Enlightenment Astronomy

William Herschel (1738-1822)

Discovery of Uranus (1781):

- First planet not known in Antiquity

On the Constructionof the Heavens(1785):

- star counts Map of the Milky Way

Greatest telescope-builderof the age

H h l F M i i A


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Herschel: From Musician to Astronomer

Organist in Bath (1766-82)

At age 35, Herschel turns to astronomy!

Composer, conductor,oboist, organist

H h l G t t T l b ild f th A


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Herschel: Greatest Telescope-builder of the Age

Caroline Herschel (1750-1848)40-foot reflector

H h l Di f U (1781)


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Herschel: Discovery of Uranus (1781)

Voyager 2 (1986)

7-foot reflector

First planet not known to the Ancients already!

Herschel: Mapping the Milky Way


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Herschel: Mapping the Milky Way

Using star counts to estimate distance

to the edge of Milky Way

Shape of Milky Way Galaxy

~10,000 lightyears

Herschel: Discovery of Infrared Radiation (1800)


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Herschel: Discovery of Infrared Radiation (1800)

Use prism to dispersesunlight into spectrum

(blue-green-yellow-red)

Place thermometer at

empty place beyond red

Detect heat there

there must exist energy(radiation) beyond red

= Infrared

Great Task Ahead: What are the Stars?


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Great Task Ahead: What arethe Stars?

still unsolved: Need better physics and chemistry!

Enlightenment Astronomy (Kant/Herschel)


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g te e t st o o y ( a t/ e sc e )

First promising explanations for stellar architecture:- Milky Way- an infinite system of `island universes (galaxies)- maybe universe is a fractal (infinite regression of worlds)?- no incontrovertible proof yet: need stellar distances!

Proof Earths motion around Sun:

- Bradleys `aberration of starlight

A mechanistic (clockwork) universe

- Laplaces Demon

- a fully deterministic universe

the history and philosophy of astronomy lecture 15: enlightenment: kant, herschel. presentation

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