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Copernicus and Galileo

2.3

New Scientific Ideas

Copernicus – published the heliocentric model. The idea that the earth was not the center of the universe. That the sunwas at the center instead. This challenged the thoughts of the Church, and they forced him to recant

Galileo – his observations by telescope verified theheliocentric model.

Geocentric model- the earth was the center of the universe.

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The reasons for seasons – the Earth travels around the sun, and its axis of rotation is tilted by 23.5 degrees to the plane of the orbit. In July, the northern hemisphere is getting more sunlight than in January.

The heliocentric model

The Copernican Revolution

Nicolaus CopernicusThe Earth moves, in two ways.• It rotates on an axis (period = 1 day).• It revolves around the sun (period = 1 year).

Galileo’s discoveries in Astronomy

Galileo did not invent the telescope, but when he heard about the invention he figured out how to build telescopes. He had the best telescopes of his time. He was the first person to use telescopes to look at the heavenly bodies. He was first, so he made the discoveries.

Craters and mountains on the moon Moons of Jupiter Phases of Venus The Milky Way consists of innumerable stars. Sunspots move across the sun’s face.

All of these favored the Copernican (heliocentric) model.

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Galileo’s sketch of the moon as seen from his telescope

A photograph of the moon

Instead of believing the moon was a smooth surface, Galileo drew the surface of the moon with craters and hills, which he could see from his telescope.

Galileo made many specific discoveries in astronomy, through observations by telescope.

The general implications…

● The planets are objects like the Earth – masses – rather than some kind of special heavenly objects. Or, to put it another way, the Earth is just another planet.

● The planets, including Earth, travel around the sun.

● The Universe is a lot bigger than we can see by the naked eye.

These ideas could be dangerous.

His Church decided that the heliocentric model was a heresy.

But Galileo continued to argue in favor of the theory, and published his reasoning. The Inquisition in Rome accused him of heresy, and required him to answer.

Found guilty of “suspicion of heresy,” Galileo recanted publicly. [A story, probably not true, is that he muttered “Eppur si muove” – “And yet, it does move.”]

He was put under arrest and sentenced to prison. But because of his fame and age (70 years old at that time) he was allowed to serve under house arrest in Florence, for the remaining years of his life.

The Trial of Galileo

Is there a conflict between Science and Religion?

There is no major conflict today, but there have been conflicts in the past, e.g. the trial of Galileo. Another example is the conflict between Darwin’s theory of evolution and the literal interpretation of the Book of Genesis ().

That latter conflict survives today in the controversy about teaching Creationism in public schools.

Pope John Paul II ordered a review of the trial of Galileo. Did the Inquisition make mistakes?

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Their work was finished in 1992.On October 31st, Cardinal Poupard delivered the final report during a papal audience. The fifth paragraph reads:

“Certain theologians, Galileo’s contemporaries, being heirs of a unitary concept of the world universally accepted until the dawn of the seventeenth century, failed to grasp the profound, non-literal meaning of the Scriptures when they described the physical structure of the created universe. This led them unduly to transpose a question of factual observation into the realm of faith.

It is in that historical and cultural framework, far removed from our own times, that Galileo’s judges, unable to dissociate faith from an age-old cosmology, believed quite wrongly that the adoption of the Copernican revolution, in fact not yet definitively proven, was such as to undermine Catholic tradition, and that it was their duty to forbid its being taught. This subjective error of judgment, so clear to us today, led them to a disciplinary measure from which Galileo had much to suffer. These mistakes must be frankly recognized, as you, Holy Father, have requested.”

(L’Osservatore Romano, November 1, 1992)

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Science and Religion

Modern science has discovered that the Earth and solar system have changed dramatically in time, over a period of billions of years since its creation.•Age of Earth ~ 4.5 Gy

•Geological processes•Ice ages•Biological evolution

This scientific understanding conflicts with a strict literal interpretation of the Book of Genesis.But science does not know (maybe cannot know) how the universe was created.

Each person must decide what to believe, but may not impose his beliefs on others.

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Johannes Kepler (1571 – 1630)

… discovered three empirical laws of planetary motion in the heliocentric solar system

1. Each planet moves on an elliptical orbit.2. The radial vector sweeps out equal

areas in equal times. 3. The square of the period is proportional

to the cube of the radius.(needed for the CAPA)

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How did Kepler determine the planetary orbits?

Compare the heliocentric model to naked-eye astronomy

The most complete data had been collected over a period of many years by Kepler’s predecessor, Tycho Brahe of Denmark.

The inner planet is Earth; the outer one is Mars. Plot their positions every month. Mars lags behind the Earth so its appearance with respect to the Zodiac is shifting.

Earth

Mars

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Astrology…

a persistentsuperstition

It’s all nonsense, of course. The motions of the planets are prescribed by natural laws of motion and gravity. How can their motion predict the future?

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Ellipse Geometry

To draw an ellipse: Take a string. Tack down the two ends. Put a pencil in the string and pull the string taut. Move the pencil around keeping the string taut.

An ellipse is the locus of points for which the sum of the distances to two fixed points is fixed.

The two fixed points are called the focal points of the ellipse.

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Parameters of an elliptical orbit (a,e)

► Semi-major axis = a = one half the largest diameter

► Eccentricity = e = ratio of the distance between the focal points to the major diameter

For example, this ellipse has a = 1 and e = 0.5.

Perihelion = r2 = 0.5 Aphelion = r1 = 1.5

► Perihelion and aphelion

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Example.Determine a, e, r1, r2.

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Isaac Newton

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The observed solar system at the time of Newton

SunMercuryVenusEarthMarsJupiterSaturn

(all except Earth are named after Roman gods, because astrology was practiced in ancient Rome)

Three outer planets discovered later…Uranus (1781, Wm Herschel)Neptune (1846 Adams; LeVerrier) Pluto (1930, Tombaugh)

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To explain the motion of the planets, Newton developed three ideas:

1. The laws of motion2. The theory of universal gravitation3. Calculus, a new branch of mathematics

Newton solved the premier scientific problem of his time --- to explain the motion of the planets.

Isaac Newton

“If I have been able to see farther than others it is because I stood on the shoulders of giants.”

--- Newton’s letter to Robert Hooke,perhaps referring to Galileo and Kepler

mF

a

221

r

mGmF

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Newton’s Theory of Universal GravitationNewton and the Apple

(The apple never fell on his head, but sometimes a stupid person will say that, trying to be funny.)

Newton asked good questions the key to his success.

Observing Earth’s gravity acting on an apple, and seeing the moon, Newton asked whether the Earth’s gravity extends as far as the moon.

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Quiz Question

Who discovered that the orbit of a planet is an ellipse?