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The Solar System


The Solar System 7/14/06 ISP 209 - 3A OUTLINE 1/ Introduction (10 min) 2/ Copernicus (15 min) 3/ Galileo (20 min) 4/ Kepler (20 min) 5/ Newton (15 min) DEMOs 1 ... – PowerPoint PPT presentation

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Title: The Solar System

The Solar System
The Solar System
The solar system
Sun Planets Asteroids Comets
Pluto Neptune Uranus Saturn Jupiter Mars Earth Ven
us Mercury Sun
Historical figures in the Copernican Revolution
Ptolemy the geocentric model, that the Earth is
at rest at the center of the Universe.
Copernicus published the heliocentric model.
Galileo his observations by telescope verified
the heliocentric model.
Kepler deduced empirical laws of planetary
motion from Tychos observations of planetary
Newton developed the full theory of planetary
The Copernican Revolution
Nicolaus Copernicus
  • The Earth moves, in two ways.
  • It rotates on an axis (period 1 day).
  • It revolves around the sun (period 1 year).

Where is this?
Inscription By reforming astronomy he initiated
modern science.
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The heliocentric model
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.
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The Copernican Model
Galileo Galilei
Galileos 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 suns face.
  • All of these favored the Copernican
    (heliocentric) model.

Galileos sketch of the moon as seen from his
A photograph of the moon
What do you think of the foremost philosophers
of this university? In spite of my oft repeated
efforts and invitations, they have refused, with
the obstinacy of a glutted adder, to look at the
planets or Moon or my telescope. (letter to
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
  • ? The Universe is a lot bigger than we can see by
    the naked eye.

These ideas could be dangerous.
The Trial of Galileo
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.
Is there a conflict between Science and
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
Darwins 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
Pope John Paul II ordered a review of the trial
of Galileo. Did the Inquisition make mistakes?
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, Galileos
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 Galileos 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. (LOsservatore Romano, November 1,
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
  • 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
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.
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
  • The square of the period is proportional to the
    cube of the radius.

(needed for the CAPA)
How did Kepler determine the planetary orbits?
Compare the heliocentric model to naked-eye
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.
The most complete data had been collected over a
period of many years by Keplers predecessor,
Tycho Brahe of Denmark.
Astrology a persistent superstition
Its all nonsense, of course. The motions of the
planets are prescribed by natural laws of motion
and gravity. How can their motion predict the
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.
Parameters of an elliptical orbit (a,e)
? Semi-major axis a one half the largest
? 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 and aphelion
Perihelion r2 0.5 Aphelion r1 1.5
Example. Determine a, e, r1, r2.
Isaac Newton
The observed solar system at the time of Newton
Sun Mercury Venus Earth Mars Jupiter Saturn
(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)
Isaac Newton
Newton solved the premier scientific problem of
his time --- to explain the motion of the planets.
To explain the motion of the planets, Newton
developed three ideas
  • The laws of motion
  • The theory of universal gravitation
  • Calculus, a new branch of mathematics

If I have been able to see farther than others
it is because I stood on the shoulders of
giants. --- Newtons letter to Robert
Hooke, perhaps referring to Galileo and Kepler
Newtons Theory of Universal Gravitation
Newton and the Apple
Newton asked good questions ? the key to his
Observing Earths gravity acting on an apple, and
seeing the moon, Newton asked whether the Earths
gravity extends as far as the moon.
(The apple never fell on his head, but sometimes
a stupid person will say that, trying to be
Quiz Question
Who discovered that the orbit of a planet is an