Modern Astronomers


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I) Modern Astronomers

A) Copernicus (1473 – 1543)

1) Founder of modern astronomy

2) Clerical position

(a) Deep abiding respect for Christianity

3) Investigations carried on alone

(a) Observations completed with the naked eye

4) Published an unsigned pamphlet in 1507

(a) Helio-centric theory

5) De Revolutionibus

(a) Completed in 1530

(b) Original manuscript lost for over 300 years

(1) Found in Prague, 1850

(c) Asserted earth rotated on its axis once daily

(d) Traveled around the sun yearly

(e) Opposite of the Ptolemiac theory

(f) Did not publish his theory

(1) Circulated amongst astronomers

(i) Concerned with Church opinion

1. Man was next to God and hence superior to all and therefore could not be “perfected”

(ii) Felt it was “un-finished”

(2) George Rheticus

(i) Mathematics professor

(ii) Two year house guest of Copernicus

(iii) Helped to publish his book

1. Published when Copernicus was dying

2. Once published, created stir of controversy

a. Went against Church

b. Went against classic thought

c. Remained on listing of Church-banned books until 1863

d. "Copernicun Revolution"


Observatory at Frombork, Poland

Copernicus' Room

Oldest existing Organ - possibly built, certainly played, by Copernicus

Copernicus lies behind this section of wall in the Monastery

While he was in Italy about 1513, Copernicus visited Rome to see friends.  It was here that he wrote a short account of what has since become known as the Copernican theory, namely that the Sun (not the Earth) is at rest in the center of the Universe.  A full account of his theory was slow to take shape and was not published until the very end of Copernicus' life, under the title On the revolutions of the heavenly spheres (De revolutionibus orbium coelestium, Nuremberg, 1543.)  Copernicus is said to have received a copy of the printed book for the first time on his deathbed (he died of a cerebral hemorrhage) so as not to face persecution by his Church for going against religious dogma.

Copernicus's heliostatic belief involved giving several distinct motions to the Earth.  Consequently, it was considered implausible by the vast majority of his contemporaries and by most astronomers and natural philosophers of succeeding generations before the middle of the seventeenth century.

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B) Giordano Bruno (1548 – 1600)

1) Italian scientist

2) Audacity to go beyond Copernicus

(a) Space was boundless

(b) Sun and earth were just one of many solar systems

(c) Suggested other inhabited worlds equal or superior to ours

3) Captured by Church authorities when traveling in Europe

(a) Seven year trial

(1) Refused to recant his beliefs

(b) Condemned and burned at the stake in Rome

Giordano Bruno

While Bruno's views were considered heretical, he was ordained a Catholic priest in 1572.  Never one to accept what he was taught without probing deeper into contrary views, Bruno read various banned texts.  His ideas on astronomy were not only the belief in a moving Earth, but he also argued for an infinite universe containing other stars like the Sun and other worlds like the Earth.  Of course Bruno was aware that this contradicted the Biblical version of the universe.  Bruno also attacked Aristotle's physics and after he returned to Paris in October 1585, these views were to land him in trouble.  Bruno was invited to return to Italy and, thinking that the Catholic Church was now more tolerant following the death of the strict Pope Sixtus V, he accepted.  It is believed that the invitation was a trick to bring him before the Inquisition and Bruno fell for it.  Bruno arrived in Rome and his trial began which was to drag on for seven years.

Pope Clement VIII demanded that Bruno be sentenced as a heretic and the Inquisition passed the death sentence on him.  On hearing the sentence he responded:

"Perhaps your fear in passing judgment on me is greater than mine in receiving it."

Bruno was burned at the stake on February 17, 1600.  In doing so, the Church suffered historical consequences.  To this day, Bruno is still regarded as an infidel by the Church and is accorded no respectful submissions in any Church related literature.

Bruno states:

"...and the greatness of His kingdom made manifest; He is glorified not in one, but in countless suns; not in a single earth, a single world, but in a thousand thousand, I say an infinity of worlds..."

Does that sounds like heresy?  For a fascinating website dedicated to Bruno, click here.

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C) Tycho Brahe (1546 – 1601)

1) Hired Johann Kepler as an assistant

2) Rejected Copernicus’ findings

(a) Combined both Ptolemy’s and Copernicus’ findings

(1) Earth at center of solar system

(2) Moon and Sun revolved around Earth

(3) All other objects revolved around Sun

3) Developed new and better instruments for viewing the heavens

(a) Revolutionized astronomical instrumentation

4) Systematic approach to recording planetary movements

(a) Accurate readings to within half an arc minute

(b) Enabled Kepler to determine elliptical orbits of planets

Ptolemy's Universe

Copernicus' Universe

Brahe's Universe


In order not to go against Church teachings but giving acknowledgement to Copernicus' work, Brahe combined the epicycles of Ptolemy and the Sun-centered work of Copernicus into a universe where the Earth was still at the center and the other known planets revolved around the Sun, whilst the Sun revolved around the Earth.

"The Noble Dane: Images of Tycho Brahe"

Edouard Ender - 1855

Click here for an in-depth study of this painting.

Interesting fact about Tycho Brahe - he had a metal nose!  He had insulted one of his students and he was challenged to a duel.  Obviously he lost!  On special occasions, he would wear a very fashionable one made of silver and gold instead of a plain metal nose that he wore during his work.  It is also thought he may have died from a bladder infection caused by his inability to go to the bathroom.  Another theory about his death is that his most prized student - Kepler - murdered him by mercury poisoning!  Kepler took advantage of his teacher's death by securing all of Brahe's records and belongings before his family could obtain them.

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D) Johann Kepler (1571 – 1630)

1) Became imperial mathematician and inherited Brahe’s records upon Brahe’s death

(a) Brahe died ten days after insisting this be done upon his death

2) Using Brahe’s tables, Kepler deduce his three laws of planetary motion

(a) Orbits of the planets are ellipses with the Sun at the focus

(b) A line from the planet to the sun sweeps over equal area in equal time

(c) A planet’s orbital period squared, is proportional to its average distance from the Sun cubed

(1) P2 = A3

(i) P = period in years

(ii) A = distance in AU

1. AU = distance from Earth to Sun

a. 93 million miles

3) Laws are empirical

(a) Based on observations

(b) Do not describe the cause of motion

(c) Predict where planets will be

Johannes Kepler

1st Law: The orbits of the planets around the Sun are ellipses, with the Sun at one focus.

2nd Law: In its orbit, a planet sweeps out equal areas in equal time.

The physical reality behind this law is the observation that the planets move relatively quickly when they are in that part of the orbit which lies close to the Sun, and more slowly when they are further away from the Sun. The orbits of most of the planets are nearly circular and the distance to the Sun and the speed of the planet in its orbit only changes by a few percent.  However, it is a big effect for the comets which fly by the Sun in only a few months, but spend many years in that part of their orbit which is away from the Sun.

3rd Law: A planet's orbital period squared, is proportional to its average distance from the sun cubed.

P2 = A3

Where P = period in years; and A = distance measure in AU

Named in his honour, the Kepler Mission, launched in 2009, is the first space mission to find Earth-sized planets.

An interesting footnote about Kepler is that when he was finishing his work on Harmony of the World, his mother was charged with witchcraft.  He stopped working in order to defend her, and she was eventually released after technical objections arising from the authorities failure to follow correct legal procedures in the use of torture on her in order to get her to confess.

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E) Galileo Galilei (1564 – 1642)

1) Systematic use of the telescope for observations

2) Discoveries

(a) Moon was not smooth

(1) Conflicted with “perfect form”

(b) Milky Way made of thousands of stars too dim to see

(c) Jupiter’s moons

(1) Galilean Moons

(i) Io, Europa, Ganymede and Callisto

(ii) Gave credence to Copernicus

1. Recognized that objects other than Earth could have moons in orbit

(d) Observed sunspots on Sun

(e) Discovered Venus passed through phases similar to the moon

           (1) Meant it orbited around the Sun, not the Earth

(f) Discovered the rings of Saturn

3) Sidereus Nuncius (Starry Messenger)

(a) Publication of his telescope findings

4) Dialogue Concerning the Two Chief World Systems

(a) Controversial

(1) Supported Copernicus’ theories

(b) Bought before the Inquisition in 1633

(1) Under threat of torture and death, recanted his beliefs

(2) Sentenced to life imprisonment


Actual eyepiece used to discover the moons of Jupiter.

Galileo's right index finger is on display in Florence, Italy.  It was severed from his hand when his body was moved from one grave to another by a follower of a cult that worshipped Galileo.  There is an inscription which reads:

"This is the finger with which the illustrious hand covered the heavens and indicated their immense space.  It pointed to new stars with the marvelous instrument, made of glass, and revealed them to the senses..."

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F) Sir Isaac Newton (1642 – 1727)

1) Started as an academically poor student

2) Genius developed over a period of time

(a) Hit on the head (?)

3) Developed his three laws during 1665 – 1666 during the Black Death

(a) Laws were found to work for objects in heaven as well as Earth

(1) First astrophysicist

(b) Laws of Motion

(1) A body continues in motion in a straight line at constant speed or remains at rest, unless it is acted upon by an outside force

(2) A body’s change of motion is proportional to the force on it and the direction of the force

(i) F = ma

1. F = force

2. m = mass

3. a = acceleration

(3) when one body exerts a force on a second, the second body exerts an equal and opposite force upon the first

4) Distinguished between an objects mass and weight

(a) Weight is a force

(b) Mass is the amount of matter

5) Newton determined that for the planets to orbit the sun in elliptical trajectories, they must be subject to a force that decreases proportional to the square of their distance from the Sun; and the force must be proportional to the masses of the sun and the planet

(a) Law of Universal Gravitation

(1) F = G M m / r2

(i) F = mutual force of attraction

(ii) G = Universal gravitational constant

(iii) r = distance between body

(iv) M = mass of main object

(v) M = mass of satellite

(2) All massive objects are gravitationally attracted to all other massive objects in the universe

Sir Isaac Newton

Probably the most famous story about Newton is about the apple falling on his head leading to his "discovery" of gravity.  The story has its basis in truth.  Newton was an academically poor student and many of his peers would ridicule him because he was small and sickly.  One day a fellow student threw an apple across the yard at Newton.  Newton stood mesmerized watching the apple soar into the sky in an arc, stop, and then fall back to Earth smacking him clearly in the forehead and knocking him to the ground.  It was at this point, that a genius (in every sense of the word) was born: for shortly afterward Newton excelled in every subject in school.

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