Ancient Astronomers

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Ancient Astronomers

• Aristotle, Aristarchus, Ptolemy, Copernicus,
  Brahe, Kepler, Galileo and Newton.

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The Great Astronomers

• Our understanding of the Solar System has
  changed greatly over time, due mainly through the
  teachings of these men Aristotle, Aristarchus,
  Ptolemy, Copernicus, Brahe, Kepler, Galileo and
  Newton.

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Aristotle 384 BC-322 BC

• Aristotle was a Greek philosopher as well as
  a scientist and astronomer. This is Aristotles
  view of the Universe. The Earth is the center,
  and all other planets, including the Sun, rotate
  around it.

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Aristotle

• 1. Only on the surface of a sphere do all objects
  fall straight down.
• 2. The view of the constellations changed at
  night as one moves around the Earth
• 3. The shadow of the Earth on the moon during a
  lunar eclipse was always circular.

• Was the first to conclude the Earth was a sphere
  in 340 BC.

• His conclusion were based on three concepts

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Aristotles Evidence
1.
2.
3.
If Earth was flat shadow would look like this.
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Aristarchus310 BC- 230 BC

• Greek philosopher first to proclaim the
  Heliocentric view of the Universe

• He observed the different half of the moon was
  lighted during the half moon phases (1st and 3rd
  quarters)

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Ptolemy 83 BC-161 AD

• Claudius Ptolemy was a Greek mathematician,
  geographer, and astronomer. This is how Ptolemy
  viewed the Solar System. The Earth is still in
  the center.

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• All of the planets travel around the sun in the
  same direction, but not at the same speed
• Because of this, there may be times when Earth
  passes a planet in its orbit
• The planet will then appear to be moving in the
  opposite direction (backward)
• This is called retrograde motion
• The planet is not really moving backward (think
  about two cars traveling side by sidewhen one
  car speeds up, the other car may appear to move
  backward

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Ptolemy

• Summarized the worlds knowledge of astronomy in
  a book called the Amalgest.
• Noted the apparent motion of the planets outside
  of Earth underwent a backward motion in their
  movement.
• Came up with his Epicyclic Theory to explain
  this

Looping Motion
E
Geocentric view of the Universe
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Nicolaus Copernicus 1473-1543

• Copernicus was an astronomer and
  mathematician. He was Polish, not Greek. His
  theory about the Sun as the center of the solar
  system is considered to be one of the most
  important discoveries ever, and the starting
  point of modern astronomy.

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Copernicus

• Solidified the Heliocentric view of the Universe.
• Came up with a relative scale called the
  Astronomical Unit or AU. An AU is 1 earth-sun
  distance.

M
Max distance from Sun
Sun
E
1 A.U.
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The Whimsical Cook

• By Benjamin Franklin
• 1748

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Translation to follow...
On the 19th of this month (January), Anno 1493,
was born the famous Astronomer Copernicus, to
whom we owe the invention, or rather the Revival
(it being taught by Pythagoras near 2000 Years
before) of that generally received System of the
World which bears his Name, and supposes the Sun
in the Center, this Earth a Planet revolving
round it in 365 Days, 6 Hours, c. and that Day
and Night are caused by the Turning of the Earth
on its own Axis once round in 24 h. c.
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Translation
The Astronomer Copernicus brought back the
theory, which is named after him, that the sun
is at the center of the Solar System and the
planets revolve around the sun. The Earth has
day and night because the Earth spins once a
day.
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The Ptolomean System, which prevailed before
Copernicus, supposed the Earth to be fixed, and
that the Sun went round it daily.
Translation
The system proposed by Ptolemy said that the
Earth stays still and the Sun goes around the
Earth.
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Mr. Whitson, a modern Astronomer, says, the sun
is 230,000 times bigger than the Earth, and 81
Millions of Miles distant from it That vast
Body must then have moved more than 480 Millions
of Miles in 24 h. A prodigious Journey round
this little Spot!
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Translation
An astronomer from Franklin's time, Mr. Whitson,
calculated the Sun to be 230,000 times bigger
than the Earth (the true value is closer to
110x) and is 80 million miles from the Earth
(the true value is about 93 million miles). The
vast body of the sun must travel a circumference
of 480 million miles (a circle with a radius of
80 million miles) in one day in order to go
around the Earth in 24 hours.
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How much more natural is Copernicus's Scheme!
Ptolemy is compared to a whimsical Cook, who,
instead of Turning his meat in roasting, should
fix That, and contrive to have his whole Fire,
Kitchen and all, whirling continually round it.
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Translation
Copernicus make more sense! Ptolemy is compared
to a foolish cook who, instead of turning his
chicken on a rotisserie, holds the chicken still
and turns the entire kitchen around the chicken.
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• GEO EARTH
• HELIO SUN
• CENTRIC CENTER

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Solar System Models

• Geocentric ancient people believed that the
  Earth was the center of the universe, and all
  planets and stars moved in orbits around Earth
  (remember, the sun appears to rise and set each
  day when it is really the Earth spinning that
  causes this)
• Heliocentric this is the accepted model. It
  states that the sun is the center of the solar
  system, and all the planets move around the sun

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Geocentric Model

• Aristotle and Ptolemy believed in the
  Geocentric or Earth-centered model.

Aristotle
Ptolemy
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Heliocentric Model

• Aristarchus, Copernicus and Galileo believed
  in the Heliocentric or Sun-centered model

Galileo
Aristarchus
Copernicus
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EARTH
SUN

• The Geocentric (Earth-centered) model places
  the Earth at the center of the universe. This is
  common in ancient Greece after the discovery of
  the spherical shape of the Earth. Most Greeks
  assumed that the Sun, Moon, stars, and planets
  orbit Earth.

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Geocentric vs.. HeliocentricReaction of
Contemporaries

• Martin Luther (1483-1546) Copernicus is a
  fool who wishes to reverse the entire scheme of
  astronomy but sacred scripture tells us that
  Joshua commanded the Earth to stand still, not
  the Sun.
• Conservative who wanted to reform Church by
  returning it to a simpler, less corrupt time.
• Agitator for the abolishment of indulgences
  (payment to lessen time of deceased in
  purgatory).
• A founder of the Protestant branch of
  Christianity.
• Response of Catholic Church to threat posed by
  the Reformation Movement
• At first, tolerance of dissent and liberal
  treatment of new ideas.
• Later, institution of the Counter-Reformation and
  the Inquisition.
• Giordano Bruno (1548-1600) burned at the stake
  for advocating that stars are suns in their own
  right, and that there is a plurality of worlds
  like the Earth.
• Galileo (1564-1642)
• Ah! Here is the person to decide the debate.

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• The Heliocentric or Sun-centered model
  recognizes that the planets are orbiting the Sun.
  

It was later discovered that the sun is just a
star in the Milky Way. The Milky Way is just one
of the galaxies in the universe.
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Tycho Brahe 1546- 1601

• Danish nobleman made careful measurements of the
  positions of stars and planets for over 20 years.
• He cataloged over 1,000 stars.
• His charts are still used today
• Known for two things
• His nose- cut off in duel wore metal nose rest
  of his life.
• His death- died of his bladder bursting
• Studied Supernova explosion in 1572
• Observed Mars orbital path
• 1600 Kepler becomes his assistant.

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Tycho Brahe - An Observer

• Tycho Brahe was a prominent scholar and
  aristocrat in Denmark in the mid-late 1500's
• He made a huge number of observations of the
  stars and planets, all with the naked eye
• Even without a telescope, he was very accurate in
  his measurements
• Also recorded the appearance of comets and
  supernovae
• The Tycho supernova remnant is still visible today

Tycho (1546-1601)
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Galileo Galilei 1564-1642

• Galileo was an Italian astronomer,
  philosopher, and physicist. He is referred to as
  the Father of Astronomy. Galileo was one of
  the first people to use a telescope to observe
  the sky. In 1610 Galileo discovered Jupiters
  four largest moons. He thought that the moons
  must be orbiting the planet since they
  occasionally disappeared.

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Galileo

• Galileo looked at the Moon, and saw that it is
  covered with mountains, craters, and blotchy dark
  colored regions.
• Viewed the Sun, and saw that it is not a perfect
  sphere. There were spots that appeared to move
  across the surface over a period of a few weeks
  and appeared and disappeared.
• Recorded the Phases of Venus
• Observed the four moons of Jupiter and recorded
  the movement pattern of each.

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Galileo Galilei
"Eppur Si Muove"(And, yet it moves!")

• 1610 Siderius Nuncius (The Starry Messenger)
• Spots on the Sun!
• The Moon has mountains, craters, rocky surface
  with imperfections!
• The planet Jupiter is not a pinpoint star
  but a disc in the sky! WITH MOONS!
• Venus has PHASES like the MOON

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Galileo Galilei
Revealing great, unusual and remarkable
spectacles, opening these to the consideration of
every man, and especially of philosophers and
astronomers.
SUNSPOTS
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The Moon Has Mountains and Valleys
Galileo Galilei
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Phases of Venus
Galileo Galilei
Galileo observed that Venus showed phases
entirely like those of the moon from full to
crescent, which it must do if the Copernican
theory was correct. According to the Ptolemaic
theory Venus would have to be a perpetual
crescent.
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Jupiter Has Moons
Galileo Galilei
Galilean Moons 4 Largest moons of JupiterIo,
Europa, Callisto, Ganymede
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Galileo Galilei
1632 "Dialogo Dei Massimi Sistemi" (In Italian!
Not Latin! For the common people!) He published
his masterpiece, Dialogue on the Two Chief World
Systems, in which he had two people, one
representing the view of Ptolemy and other the
view of Copernicus, present their arguments
before an intelligent layman. Galileo of course
gave the Copernican the brilliant best of the
battle.
The Pope was persuaded that Simplico, the
character who upheld the views of Ptolemy in the
book, was a deliberate and insulting caricature
of himself. The book was all the more damaging to
those who felt themselves insulted, because it
was written in vigorous Italian for the general
public (and not merely for the Latin-learned
scholars) and was quickly translated into other
languages -- including Chinese!
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Scientific Martyr
Galileo Galilei

• Teaches Heliocentric Ideas
• Claims proof for Earths motion.
• Trial by Church (threatened with instruments of
  torture), forced to recant views (1633).
• Confined to house arrest. Formulates new
  science of mechanics.
• Loses his sight (blinded) by Sun observations
• Most influential combination of experimentalist
  and theorist world has ever seen.
• Often credited rightly with having started modern
  science.

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Johannes Kepler-
1571-1630

• Because Brahes observations of Mars orbital path
  could not be explained by Copernicuss model he
  developed Three Laws of Planetary Motions around
  1600.
• Learned the orbits of planets are not round, but
  are elliptical.

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Johannes Kepler - A Theorist

• Shortly before his death, Tycho began working
  with another scientist named Kepler
• Kepler was put to the task of creating a model to
  fit all of Tycho's planetary data
• Kepler spent the remainder of his life
  formulating a set of laws that explained the
  motion of the planets

Kepler (1571 - 1630)
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Kepler's First Law

• First Law of Planetary Motion States that the
  planets travel in elliptical orbits with the sun
  at one focus.
• Kepler first noted that the orbital path of a
  planet around the Sun is an ellipse, not a
  perfect circle
• The Sun lies at one of the foci of the ellipse
• The eccentricity of an ellipse is a measure of
  how 'squished' from a circle the shape is

Focus
Focus
Kepler's 1st Law The orbital paths of the
planets are elliptical with the Sun at one focus.
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Kepler's Second Law

• Kepler also noticed that the planets sweep out
  equal areas in their orbit over equal times
• Notice that this means the planet must speed up
  and slow down at different points
• If it takes the same amount of time to go through
  A as it does C, at what point is it moving
  faster?
• C, when it is closest to the Sun

Kepler's 2nd Law An imaginary line connecting
the Sun to any planet sweeps out equal areas of
the ellipse over equal intervals of time.
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Kepler

• Third Law of Planetary Motion
• (Period)2 (Radius)3
• Period revolution around the sun- Years
• Radius the distance from the sun. In A.U.s
  98,000,000 miles

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Kepler's Third Law

• Finally, Kepler noticed that the period of
  planet's orbit squared is proportional to the
  cube of its semi major axis
• This law allowed the orbits of all the planets to
  be calculated
• It also allowed for the prediction of the
  location of other possible planets

Kepler's 3rd Law Simplified
NOTE In order to use the equation as shown, you
must be talking about a planet in the Solar
System, P must be in years, and a must be in A.U.
!!!
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Isaac Newton1643-1727

• Born in England on Christmas day
• Plague went through Europe to escape he went to
  country home for 2 years with nothing to do he
  made his most profound discoveries and proposed
  his most startling theories.
• Came up with the three Laws of Motion.
• Developed Theory of Universal Gravitation

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Isaac Newton

• Kepler's Laws were a revolution in regards to
  understanding planetary motion, but there was no
  explanation why they worked
• That explanation would have to wait until Isaac
  Newton formulated his laws of motion and the
  concept of gravity
• Newton's discoveries were important because they
  applied to actions on Earth and in space
• Besides motion and gravity, Newton also developed
  calculus

Newton (1642-1727)
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Some terms

• Force the push or pull on an object that in some
  way affects its motion
• Weight the force which pulls you toward the
  center of the Earth (or any other body)
• Inertia the tendency of an object to keep moving
  at the same speed and in the same direction
• Mass basically, the amount of matter an object
  has
• The difference between speed and velocity
• These two words have become identical in common
  language, but in physics, they mean two different
  things
• Speed is just magnitude of something moving (25
  km/hr)
• Velocity is both the magnitude and direction of
  motion (35 km/hr to the NE)

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Newtons First Law of Motion

• An object at rest will remain at rest unless
• acted on by an unbalanced force. An
• object in motion continues in motion with the
• same speed and in the same direction unless
• acted upon by an unbalanced force.
• This law is often called "the law of inertia".

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Newton's First Law

• Newton's first law states An object at rest will
  remain at rest, an object in uniform motion will
  stay in motion - UNLESS acted upon by an outside
  force

Outside Force
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1st Law

• The moon will keep revolving around the earth
  forever, unless acted on by an unbalanced force.

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• Moon in orbit around earth

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1st Law

• Once airborne, unless acted on by an unbalanced
  force (gravity and air fluid friction it would
  never stop!

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1st Law

• Unless acted upon by an unbalanced force, this
  golf ball would sit on the tee forever.

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Newton's 1st Law and You
Dont let this be you. Wear seat belts. Because
of inertia, objects (including you) resist
changes in their motion. When the car going 80
km/hour is stopped by the brick wall, your body
keeps moving at 80 m/hour.
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• Why then, do we observe every day objects in
  motion slowing down and becoming motionless
  seemingly without an outside force?
• Its a force we sometimes cannot see friction.

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What is this unbalanced force that acts on an
object in motion?
Friction!

• There are four main types of friction
• Sliding friction ice skating
• Rolling friction bowling
• Fluid friction (air or liquid) air or water
  resistance
• Static friction initial friction when moving an
  object

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• Slide a book across a table and watch it slide
  to a rest position. The book comes to a rest
  because of the presence of a force - that force
  being the force of friction - which brings the
  book to a rest position.

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• Objects on earth, unlike the frictionless space
  the moon travels through, are under the influence
  of friction.

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• In the absence of a force of friction, the book
  would continue in motion with the same speed and
  direction - forever! (Or at least to the end of
  the table top.)

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2nd Law
F M x A
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Newton's Second Law

• Acceleration is created whenever there is a
  change in velocity
• Remember, this can mean a change in magnitude
  AND/OR direction
• Newton's Second Law states When a force acts on
  a body, the resulting acceleration is equal to
  the force divided by the object's mass
• Notice how this equation works
• The bigger the force, the larger the acceleration
• The smaller the mass, the larger the acceleration

or
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2nd Law

• The net force of an object is equal to the
  product of its mass and acceleration, or Fma.

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2nd Law

• When mass is in kilograms and acceleration is in
  m/s/s, the unit of force is in newtons (N).
• One newton is equal to the force required to
  accelerate one kilogram of mass at one
  meter/second/second.

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2nd Law (FMxA)

• How much force is needed to accelerate a 1400
  Kilogram car 2 meters per second/per second?
• Write the formula
• F M x A
• Fill in given numbers and units
• F 1400K x 2 meters per second/second
• Solve for the unknown
• 2800 K-meters/second/second or 2800 N

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If mass remains constant, doubling the
acceleration, doubles the force. If force remains
constant, doubling the mass, halves the
acceleration.
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Newtons 2nd Law proves that different masses
accelerate to the earth at the same rate, but
with different forces.

• We know that objects with different masses
  accelerate to the ground at the same rate.
• However, because of the 2nd Law we know that they
  dont hit the ground with the same force.

F ma 98 N 10 kg x 9.8 m/s/s
F ma 9.8 N 1 kg x 9.8 m/s/s
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Check Your Understanding

• 1. What acceleration will result when a 12-N net
  force applied to a 3-kg object? A 6-kg object?
•  
• 2. A net force of 16 N causes a mass to
  accelerate at a rate of 5 m/s2. Determine the
  mass.
•  3. How much force is needed to accelerate a
  66-kg skier 1 m/sec/sec?
• 4. What is the force on a 1000-kg elevator that
  is falling freely at 9.8 m/sec/sec.?
•  

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Check Your Understanding

• 1. What acceleration will result when a 12-N net
  force applied to a 3-kg object?
• 12 N 3 kg X 4 m/s/s
•  
• 2. A net force of 16 N causes a mass to
  accelerate at a rate of 5 m/s2. Determine the
  mass.
• 
  16 N 3.2 kg x 5 m/s/s
•  
• 3. How much force is needed to accelerate a 66-kg
  skier 1 m/sec/sec?
• 66 kg-m/sec/sec or 66 N
• 4. What is the force on a 1000-kg elevator that
  is falling freely at 9.8 m/sec/sec.?
•  9800 kg-m/sec/sec or 9800 N

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3rd Law

• For every action, there is an equal and opposite
  reaction.

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3rd Law

• According to Newton, whenever objects A and B
  interact with each other, they exert forces upon
  each other. When you sit in your chair, your body
  exerts a downward force on the chair and the
  chair exerts an upward force on your body.

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3rd Law

• There are two forces resulting from this
  interaction - a force on the chair and a force on
  your body. These two forces are called action and
  reaction forces.

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Newtons 3rd Law in Nature

• Consider the propulsion of a fish through the
  water. A fish uses its fins to push water
  backwards. In turn, the water reacts by pushing
  the fish forwards, propelling the fish through
  the water.
• The size of the force on the water equals the
  size of the force on the fish the direction of
  the force on the water (backwards) is opposite
  the direction of the force on the fish
  (forwards).

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3rd Law
Flying gracefully through the air, birds depend
on Newtons third law of motion. As the birds
push down on the air with their wings, the air
pushes their wings up and gives them lift.
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• Consider the flying motion of birds. A bird
  flies by use of its wings. The wings of a bird
  push air downwards. In turn, the air reacts by
  pushing the bird upwards.
• The size of the force on the air equals the size
  of the force on the bird the direction of the
  force on the air (downwards) is opposite the
  direction of the force on the bird (upwards).
• Action-reaction force pairs make it possible for
  birds to fly.

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Other examples of Newtons Third Law

• The baseball forces the bat to the left (an
  action) the bat forces the ball to the right
  (the reaction).

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3rd Law

• Consider the motion of a car on the way to
  school. A car is equipped with wheels which spin
  backwards. As the wheels spin backwards, they
  grip the road and push the road backwards.

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3rd Law
The reaction of a rocket is an application of the
third law of motion. Various fuels are burned in
the engine, producing hot gases. The hot gases
push against the inside tube of the rocket and
escape out the bottom of the tube. As the gases
move downward, the rocket moves in the opposite
direction.
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Newton
Knowing this, which heavenly body causes the
tides, the sun, or the moon which is about
400,000,000 times smaller?
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Without the contributions of Aristotle,
Ptolemy, Copernicus, and Galileo, modern
astronomers and scientists would not have been
able to develop bigger and better telescopes and
eventually enable us to go into space!
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End