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Ch. 3: The Solar System

Brief outline: Ideas of Copernicus >> Galileo >> Kepler >> Isaac Newton

This chapter discusses how the scientific contributions by Copernicus, Galileo and Kepler led to

Newton's discovery of the Universal Gravitation.

• It must be understood that the ancient Greek ‘philosophers-scientists’ had various opinions about

the ‘center of the universe’ and the relation between Earth and the Sun. Some thought that the Sun

is at the center. Others that it is Earth.

• Aristotle (384-322 BC) chose to follow the opinion that it is Earth. It appears that he also believed

that heavier bodies fall faster than light ones, and many other things.

• Much later in 312 AD Constantine was made emperor of Rome and protector of Christianity.

Christianity evolved rapidly after the council of Nicaea (AD 325), when intellectuals/philosophers

within the Catholic church made efforts to establish doctrine that would make the ideas found in the

bible more complete, and eventually added concepts of both Plato and then Aristotle.

• Once this was done it became DOGMA of the church, and to attack this view was to attack the

foundation of the church. And so this incorrect view lasted for over 1,000 years, until Copernicus.

<Nicolaus Copernicus> (1473-1543)

Ideas

The earth is NOT the center of the universe, although it is

the center of the moon’s orbit and of its own gravity.

The sun is the center of the

planetary system and the sphere of stars.

Earth is just one of the planets.

Since the moon rotates around the Earth, the heavenly bodies do

not share the same center.

The Earth’s distance from the sun is negligible compared to the

distance to the fixed stars.

The stars, therefore, are vast objects lying at great distances from the Sun and the Earth.

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Although the heavens appear to rotate around the Earth once a day, it is the Earth that

rotates on its own axis.

The Sun appears to move completely around the sky once a year, but this is due to the

revolution of the Earth around the Sun.

The complex movements of the planets, which include points of apparent rest and periods

when they seem to reverse their normal march across the sky (retrograde motion), along

with their brightening and dimming, can be explained by the relative motions of each planet

& The Earth.

Placing the sun at the center resolves all ambiguities about the order of the planets. The

further the orbits from the sun, the longer they take to circle it. Mercury is the closest and in

the least time, 88 days, while distant Saturn takes 30 years to circle the sun.

Method

Few astronomical observations

Relied more on ancient and unreliable sources.

Was put off by a basic inconsistency

Was very conservative

Feared scorn

Appreciated orders

Was very cautious of his ideas

His theories were based on knowledge of his predecessors.

Lack of vision, brilliance, fire.

Was fearful, stubborn, miserly, obsequious to authorities,

arrogant toward others, and a procrastinator.

Impact

Overturned two thousand years of astronomical thinking (perception that the earth stands

still while the heavens wheel around it)

Gave birth to our present concept of the solar system.

Galileo, Kepler and Newton built on his foundation (De Revolutionibus) and their work

cumulatively destroyed the ancient view of a finite, womb-like cosmos with the Earth & The

Human Race at its center.

<Johannes Kepler> (1571-1630)

Ideas Kepler (eventually) managed to get access to the observational

equipment of Tycho Brahe (1546-1601), a very wealthy guy who

loved astronomical observations and made very

careful and accurate observations of the planets

daily. Kepler needed this data to formulate his

three rules of planetary motion around the Sun.

The Universe was constructed on the basis of

Geometric figures.

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Three laws of planetary motion

o Confirmed Copernicus’s heliocentric theory while modifying it in some way.

First Law - The orbits of the planets around the sun

were not circular but elliptical in shape with the sun at one

focus of the ellipse rather than at the center.

o Rejected Copernicus

Second Law - The speed of a planet is greater when it is

closer to the sun and decreases as its distance from the sun

increases.

o Destroyed a fundamental Aristotelian Tenet that

the motions of the planets were steady and unchanging.

Third Law - Planets with larger orbits revolve at a

slower average velocity than those with smaller orbits.

Method

Great interest in Math and Astronomy

Was an avid Astronomer

Keen interest in Hermetic thought and

Neoplatonic mathematical magic

Modification

Observation

Solid Evidence

Impact

The three laws effectively eliminated the idea of uniform circular motion as well as the idea

of crystalline spheres revolving in circular objects.

People had been freed to think in new terms of the actual paths of planet revolving around

the sun in elliptical orbits.

Caused the Ptolemaic system to rapidly lose ground to new ideas.

Important questions still remained unanswered: What were the planets made of?! And how

does one explain motion in the universe - led to Galileo Galilei to answer.

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<Galileo Galilei> Ideas

Observed sunspots - The Universe is not unchanging

The moon was just like the surface of the Earth as it had mountains and depressions.

Invented the telescope

Milky Way had separate stars.

Jupiter was like a miniature planetary system.

Charted the orbits of its moons

Designed instruments such as a thermometer and a mechanical calculating device, his

geometric and military compass.

A nova or a new star, in the constellation Serpentarius, lay in the supposedly unchanging

regions beyond the moon.

Scribed phases of Venus

Rotation of the sun

The Copernicus theory was true.

Outlined and explained the scientific

method in his book The Assayer. In it,

Galileo set out his views on scientific reality

and on the new scientific method; he

explained his doctrine of primary qualities

(which were those that could be measured)

and secondary qualities (which were not

measurable, i.e. qualities like odor and taste).

In The Assayer, he also explained how to define a problem with the help of preliminary

experiments and, from the results, to form a theory, which could then be used to ‘predict’

consequences that could be observationally tested.

It was in The Assayer, too, that he made his famous remark, “The Book of Nature is …...

written in mathematical characters”. Published the Starry Messenger in Italian (instead of Latin - the language of the learned)

which helped in the spread of the observations he made using his telescope. NOTE: He did

not mention about the heliocentric universe in the Starry Messenger. He supported the

heliocentric universe in his another publication the Dialogue Concerning the Two Chief

World Systems.

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Method

Proved or disproved competing theories not just through logic but

through experimentation. - Father of Modern Science/Father of

Mathematical Physics - invented the scientific method which was later

refined by Isaac Newton

Realized that Science must be built on measurement & Mathematics

Observations

Careful Drawing

Insisted on writing in Italian rather than Latin - More spread of his

ideas

Bold & Expansive mind, indefatigable observation & experimentation

Impact

He turned Copernicus’s heliocentric theory into demonstrate able fact.

His careful drawings of Jupiter’s retinue of moons, phases of Venus, and spots defacing the

Sun, made the issues on the truth real.

Cast doubt on people about the Earth’s position & God’s location.

Broadcasted his radical ideas to the masses

Casted the church to be under doubt. It was no longer mathematics. Either the Earth

and Humanity lay at the center of creation as the Church decreed or they wandered

insignificantly through space.

His pugnacious courage, blazed on indelible trail for all scientists to come.

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<Sir Isaac Newton>

Ideas

The three laws of motion:

1) Every object continues in a state of rest or uniform motion in a

straight line unless deflected by a force

2) The rate of change of motion of an object is proportional to the

force acting upon it.

3) To every action, there is always an equal and opposite reaction.

Demonstrated that the three laws of motion govern the planetary

bodies as well as terrestrial objects

Universal law of gravitation (in his Mathematica Pricipatia): Every object in the Universe was attracted to every other object

with a force (gravity) that is directly proportional to the product of their

masses and inversely proportional to the square of the distances in

between them.

Method

Interest in Mathematics, Invention and

philosophy. Extreme interest in aspect of the occult world.

Was not the first of reason, was last of

magicians. Believed that clues about mysteries about the

world were to be found partly in evidence of the

heavens and in the construction of elements, but also partly in certain papers or traditions

handed down from the past.

Considered himself a representative of the

Hermetic Tradition.

Spelled out the Mathematical Proofs showing

his Universal laws of Gravitation

His work was the culmination of the theories

of Copernicus, Galileo, and Kepler. Applied his theories of mechanics to the

problems of astronomy.

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Impact 1666

Invented the calculus

Investigated into the composition of light

Inaugurated his work on the law of Universal Gravitation

1684

Wrote the Principia (Mathematical Principals of Natural Philosophy)

1686

Pieced together a coherent synthesis for a new cosmology. Demonstrated that one universal law mathematically proven could explain all motions in

the universe. Gave the idea that The Secrets of the natural world could be known by human

investigation. Created a new cosmology in which the world was seen largely in mechanistic terms.

The world view of the West was dominated by Newton’s world-machine, conceived as

operating absolutely in time , space, & motion, until the 20th century. Ideas were soon accepted and reinforced by developments into their fields especially

medicine.

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. 6.24 (CP): A summary of the process by which our solar system formed, according to the nebular theory.

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Materials in the solar

nebula.

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Fig. 6.17 (CP): Temperature differences in the solar nebula led to different kinds of condensed materials, sowing the seeds of two different kinds of planets.

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Illustration of the asteroid belt, Kuiper belt & Oort cloud

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• Things that are moving rapidly across the night sky can be: bird, plane, satellite, Superman or meteoroid: comet or asteroid