Download Sir Isaac Newton

By Ken Journigan
Independence High Astronomy
The History of
Astronomy
Astronomical History
A very complete story of astronomy is
told in its history. The men and
women of astronomical history are
synonymous with the historical
evolution of this observational science.
Universal Models
The
Geocentric Model Supporters
The Geocentric Model of the Universe
With one mere exception (to be named later),
ancient astronomers placed the Earth at the
center of the known Universe. This Universal
Model was known as the Geocentric Model.
“Geo” meaning Earth and “centric” meaning
centered.
Aristotle (384 BC – March 7, 322 BC)
Aristotle was an ancient Greek philosopher, a student
of Plato and teacher of Alexander the Great. Aristotle
had a strong influence, and his teachings carried great
weight. He promoted the geocentric model.
According to Aristotle the cosmos were composed of
five fundamental properties
 Earth
 Air
 Water
 Fire
 The spherical shells of
heavenly bodies with Earth
at the center
Aristotle
Aristotle believed that everything in the
regions outside the Earth was perfect and
eternally unchanging. All objects in the
heavens were supposed to be perfect
circles, except for stars, which were
featureless points of light.
Aristotle
Aristotle’s beliefs about the geocentric model of
the universe would pervade astronomy to such
an extent, that they would not be challenged for
another 1500 years.
Plato and Aristotle
The Greek Astronomer Hipparchus
Hipparcus (c. 190 BCE--c. 120 BCE) was born in Nicaea, a
city in what is now Turkey. In the year 135 BCE, he was
stargazing and saw a bright point of light he didn't recognize.
This star appeared in
the constellation Scorpio.
It turned out to be a
supernova. This disproved
Aristotle’s idea of the
perfect, unchanging Universe
The Greek Astronomer Hipparchus
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Developed the first catalog of stars
Developed a magnitude scale
where 1 represented the brightest
stars and 6 represented the
dimmest stars.
Determined the precession
of Earth based on records
from the past and compared
it to his own observations
The Greek Astronomer Hipparchus
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Hipparchus had a problem making his star chart. It was
easy enough to map the surface of the Earth, because the
Earth has landmarks: rivers, mountains, cities--places of
known location, to which other places can be compared.
The sky, however, has no landmarks, just the stars
themselves. Hipparchus decided to invent "landmarks"
of his own. He picked one point in the sky and drew
imaginary lines radiating out from it, like the spokes of
a wheel. Then he drew circles around this central point
which grew larger and larger.
The Greek Astronomer Hipparchus
This made a grid around the sky, on which Hipparchus could
locate any star he wanted. This idea soon improved Earthly mapmaking as well: the modern lines of longitude and latitude come
directly from Hipparchus's method of mapping the sky.
Instead of locating stars on the "celestial sphere" (the entire
area visible around the Earth),
later map-makers drew
gridlines on their charts
of the Earth's sphere.
Eratosthenes and Size of the Earth
About 200 BC, Eratosthenes used Aristotle's ideas to
calculate the size of the Earth. On a certain day of the
year, observers at Syene, Egypt saw the sun directly
overhead. Observers at other locations (Alexandria,
Egypt) saw the sun at an angle on that day. The angular
displacement was measured.
 Using simple geometry, he
calculated the circumference
and the radius of the Earth.
 The result was within 1 percent
accuracy of the figure known today.
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Ptolemy
Ptolemy’s full Latin name was Claudius
Ptolemaeus (fl. AD 127-145, Alexandria), He
was an ancient astronomer, geographer, and
mathematician who considered the Earth the
center of the universe
(the "Ptolemaic system").
Virtually nothing
is known about his life.
The Ptolemaic Model
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The Ptolemaic model accounted for the
apparent motions of the planets in a very direct
way, by assuming that each planet moved on a
small sphere or circle, called an epicycle, that
moved on a larger sphere or circle, called a
deferent. The stars, it was assumed, moved on a
celestial sphere around the outside of the
planetary spheres.
The Epicycle
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http://physics.syr.edu/courses/java/demos/ken
nett/Epicycle/Epicycle.html
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The idea of the epicycle was incorporating into
Ptolemy’s universal model in order to explain
retrograde motion
Prograde Versus Retrograde Motion
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Prograde Motion: The regular east to west
migration of celestial bodies across the sky.
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Retrograde Motion: The irregular and periodic
transit of planets across the sky from west to
east.
Universal Models
The
Heliocentric Model
Supporters
The Heliocentric Model
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Heliocentric (sun-centered) model
More accurately accounted for all observations
of the movement of the sun and the moon, and
the planets, and the stars
were good predictors of future positions of
celestial bodies; models were verifiable
simplicity (Occam's Razor or the Principle of
Parsimony) - as few assumptions or rules as
possible; no contradictions.
Heliocentric Model
Aristarchus of Samos, a Greek about
310-230 BC, had a heliocentric model. He
proposed that all of the planets, including
Earth revolved around the Sun, and that
the Earth rotates on its axis once a day. His
ideas did not gain widespread acceptance
during his lifetime.
Aristarchus of Samos
Aristarchus was the first person to give the solar
system scale.
Nicholaus Copernicus and the Revival
of the Heliocentric Universe.
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Nicholaus Copernicus was a Polish cleric
(1473-1543) that lived around 1500. He was
dissatisfied with the complexity of the
geocentric model. His beliefs would ultimately
get him in trouble with the Church.
Nicholaus Copernicus and the Revival
of the Heliocentric Universe.
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His ideas included:
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Sun is at the center of the universe, motionless; stars are
motionless around the edge
Planets all revolve around the sun (6 total including Earth)
Moon revolves around Earth
Earth rotates on axis causing apparent daily motion of the
heavens
Earth revolves around sun causing sun's annual movements
Retrograde motion of planets is due to relative planetary
motions
Planetary orbits are perfect circles
Nicholaus Copernicus and the Revival
of the Heliocentric Universe.
Copernicus was the first to accurately determine
the relative distances of the planets from the
sun.
Planetary Distances According to
Copernicus
Planet Copernican Distance
Real Distance
Mercury
0.38 AU
0.39 AU
Venus
0.75 AU
0.72 AU
Earth
1.00 AU
1.00 AU
Mars
1.52 AU
1.52 AU
Jupiter
5.22 AU
5.20 AU
Saturn
9.17 AU
9.54 AU
Copernican views marked the beginning of the modern
era of astronomy.
Tycho Brahe
Over a 20 year period of time, Tycho Brahe
made consistent observations which supported
the heliocentric theory proposed earlier by
Copernicus. These observations were made
using only a compass and
a sextant.
Brahe catalogued
over 1000 stars.
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Kepler's First Law
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The orbit of each planet is an ellipse with the
sun at one focus.
Kepler's Second Law
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The line segment joining a planet to the sun
sweeps out equal areas in equal time intervals.
Kepler's Third Law
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The square of the period of revolution of a
planet about the sun is proportional to the cube
of the semi-major axis of the planet’s elliptical
orbit.
Kepler's Laws
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Kepler provided us with a tool, accurate even by
today’s standards, to understand the mechanical
universe and the orbital nature of the planets.
The only remaining question, was why did the
planets move the way they did?
The answer to that question could be provided
by only one man; arguably the greatest scientist
the world has ever seen…….
Sir Isaac Newton
…But first, what about Galileo?
Galileo Galilei
1564 - 1642
Galileo Galilei
His observations included:
 First to use the telescope for observations
 Mountains on the Moon.
 The Galilean moons of Jupiter.
 The phases of Venus.
 Saturn and its rings (though he did
not understand why they periodically
disappeared).
 Sunspots.
Galileo Galilei
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Convicted of heresy, Galileo was placed under house
arrest for the remainder of his life, a gentle punishment
for any individual convicted during the Inquisition.
On 31 October 1992, 350 years after Galileo's death,
Pope John Paul II gave an address on behalf of the
Catholic Church in which he admitted that errors had
been made by the theological advisors in the case of
Galileo. The Church however never admitted that they
were wrong in declaring Galileo a heretic!
Sir Isaac Newton (1642-1727)
Sir Isaac Newton
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Newton’s first major publication regarded his
invention, design and construction of the first
reflecting (or Newtonian) telescope.
Eliminated chromatic aberration.
Sir Isaac Newton
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In 1684, three members of the Royal Society, Sir
Christopher Wren, Robert Hooke and Edmond Halley,
argued as to whether the elliptical orbits of the planets
could result from a gravitational force towards the sun
proportional to the inverse square of the distance.
Halley writes:
Mr. Hook said he had had it, but that he would conceal it for
some time so that others, triing and failing might know how to
value it, when he should make it publick.
(Yea, right!!! What a load!)
The Ideas of Isaac Newton
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The central topic of the Principia was gravitational
force. Defined by Newton as:
Fg = G (M1) (M2)/ r2 where: (the inverse square law)
Fg = The force of gravity
G = The gravitational constant
M1 = The mass of body one
M2 = The mass of body two
r = the distance between the centers of the two bodies
Sir Isaac Newton
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Orbital flight was explained by Newton in a
though activity called the “mountain cannon”.
Is seeks to show how an object may continually
fall and still never his the ground of a round
body.
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http://galileoandeinstein.physics.virginia.edu/m
ore_stuff/Applets/newt/newtmtn.html
Newton’s First Law of Motion
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Newton’s First Law of Motion states that:
F = ma
F = force
m = mass
a = acceleration
where:
Newton’s Second Law of Motion
Newton’s Second Law of Motion is the Law of
Inertia which states that:
A body in motion tends to stay in motion (in a
straight line) and a body at rest tends to stay at
rest, unless acted upon by some external force.
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Mass resists change and the natural state of
matter is to be in motion!
Newton’s Third Law of Motion
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Newton’s Third Law of Motion states:
For every action there is an equal, but opposite,
reaction.
Or, if I push you, then you push me and
if you push me then I push you!
Isaac Newton
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Creator of:
Reflecting telescope
Laws of Motion
Laws of Gravity
Calculus
Astrophysics
Our understanding of the true nature of light
(Not a bad resume, eh?)