The Copernican Revolution!!!

Nicolaus Copernicus, 1473-1543

! Polish physician ! and lawyer

! Revived Aristarchus’ idea of a Sun-centered universe! Heliocentric

! Planets move in circular orbits about Sun

! Retrograde motion explained automatically;! No need for epicycles and

deferents, etc.! Measured relative sizes of

planets’ orbits

Around 1514 he distributed a little book, to a few of his friends who knew that he was the author even though no author is named on the title page. This

book, usually called the Little Commentary, set out Copernicus's theory of a universe with the sun at its center.

1. There is no one center in the universe.2. The Earth's center is not the center of the universe.3. The center of the universe is near the sun.4. The distance from the Earth to the sun is imperceptible compared

with the distance to the stars.5. The rotation of the Earth accounts for the apparent daily rotation

of the stars.6. The apparent annual cycle of movements of the sun is caused by

the Earth revolving round it.7. The apparent retrograde motion of the planets is caused by the

motion of the Earth from which one observes.

Nicolaus Copernicus, 1473-1543

! Ideas did not find ready acceptance! His model did not give much better agreement

with observation than Ptolemy’s! Blame lies partly on choice of circle

! the perfect curve

! Model implies parallax shift in star position! none seen

! Earth feels at rest! no sensation of motion

! Authority of Aristotle ! and the Church

Nicolaus Copernicus, 1473-1543

Aristotle

In Copernican astronomy one now had to assume that the orbit of the Earth was as a point with respect to the fixed stars, and because the fixed

stars did not reflect the Earth's annual motion by showing an annual parallax, the sphere of the fixed stars had to be immense.

Copernicus’s Heliocentric DiagramPrinted in De Revolutionibus

Forbidden!!!" In 1616 the Catholic Church placed Copernicus’ work on its list of forbidden books “until corrected” by local ecclesiastical censors, where it remained until 1835!

Martin Luther described him as “an upstart astrologer…This fool wished to reserve

the entire science of astronomy. But sacred scripture tells us that Joshua commanded the Sun to

stand still, and not the Earth.”

Tycho Brahe,1546-1601

! Danish nobleman; owned an island castle! Imperial Mathematician to the Holy

Roman Emperor, Rudolph II! Built instruments of high accuracy

! no telescopes yet! Made precise measurements of planet

positions! Observed a “new” star in 1572

(supernova)! Heavens are changeable!

! The supernova showed no parallax! much farther than planets

Uraniburg

A New Star, 1572

Tycho’s Observatory

Tycho’s observatory at Uraniborg, Denmark. Tycho is seen showing the mural quadrant, a marked quarter circle on the wall, that he used to measure the altitudes at which the stars and planets crossed the meridian.

Tycho Brahe, Continued

! Studied path of a comet in 1577! The comet would have had to pass through

many of the perfect crystalline spheres! Liked Copernicus’ model but could not get

over the “lack of stellar parallax” objection.! A New Model

! Planets circle the Sun! Sun circles the Earth

Interesting Useless Fact: Lost nose in a duel, wore a metal one.

This Tychonic world system became popular early in the seventeenth century among those who felt forced to reject the Ptolemaic arrangement of the planets (in which the Earth was the center of all motions) but who, for various reasons, could not accept the Copernican alternative.

Johannes Kepler, 1571-1630

! Tycho’s assistant; came from a desperately poor background

! Kepler’s Cosmic Mystery! “Inherited” Tycho’s notebooks! Very carefully analyzed records

for Mars and concluded that … ! Mars and other planets move in

elliptical orbits, not circular ones! The Sun is at the focus of the

ellipse, not at its center

Kepler: Mystery of the CosmosMysterium Cosmographicum, 1596

! Kepler’s Cosmic Mystery – The spheres of the six planets nested in the five perfect solids of Pythagoras and Plato.

! The outermost perfect solid is a cube.

The Laws

Kepler’s LawsFirst Truly Mathematical Description

! All planets move in elliptical orbits, with the Sun at one focus of the ellipse

! Line from the Sun to a planet sweeps out equal areas in equal intervals of time

! Square of period (in years) = cube of orbit size (in AU)

P2 = R3

Kepler’s Second Law

The two shaded sectorsare equal in area.

A Third Law Example

We know from observations that it takes Jupiter 11.86 years to revolve around the Sun. What is Jupiter’s distance from the Sun?

P2 = R3

! Let P = 11.86 years

! Then P x P= 11.86 x 11.86 = 140.66! Therefore, R x R x R = 140.66

R = 5.2 A.U.

Galileo Galilei, 1564-1642

! Italian scientist and scholar! Studied motion of objects, but did not drop stones

from the Leaning Tower of Pisa! First one to look at the sky with a telescope, 1609! Saw craters and hills on Moon

! It’s a piece of rock, not something special! Saw spots on the Sun; spots shifted in time

! Sun is neither perfect, nor unchanging

The Moons of Jupiter! 1610 - Galileo publishes Sidereus

Nuncius (Message from the stars) which describes the astronomical discoveries he has made with his telescopes.

! Harriot also observes the moons of Jupiter but does not publish his work. Observed four moons moving around Jupiter

There are other centers of motion besides “us”

Galilean Moons

Galileo’s Moon Drawing

Sunspots Observed by Galileo

Dialogue Concerning the Two World Systems

! Saw immense numbers of stars in the Milky Way

Existing conceptions of universe too limited

! Saw phases of Venus

Phases, position and apparent size of Venus could only mean that it orbited the Sun

Ran into serious trouble with the Church; Galileo recanted

then; the Church in 1992!

A great book by Dava Sobel!