The Solar System

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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)

Slide 20

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.

Slide 21

Johannes Kepler (1571 – 1630)

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

Each planet moves on an elliptical orbit.

The radial vector sweeps out equal areas in equal times.

The square of the period is proportional to the cube of the radius.

(needed for the CAPA)

Slide 22

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

Slide 23

Astrology…

a persistent

superstition

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?

Slide 24

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.