Chapter 1 The Copernican Revolution

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Chapter 1The Copernican Revolution
AST1002 Introduction to Astronomy Dr. Mike
Reynolds
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Early Astronomy

• As one of the oldest sciences, if not the oldest,
  astronomy was important in the day-to-day lives
• Calendars important due to agriculture seasons
  and time
• Oldest Calendar found dates to 4800 BC
  Egypt-Sudan border
• Some African Calendars had the ability to predict
  lunar phases
• Navigation
• Simple Human Curiosity

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SoWhat Time Is It?

• During the day
• People observed the Suns path
• Shadows pre-sundials
• During the night
• Moons position and phase
• Star positions
• During the Year
• Suns seasonal position

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Other Observations?

• Ancient Civilizations observed positions of
  specific stars and planets
• Rising and setting times
• ?Ancient observatories were built to do this
  fairly accurately
• Mayan observatory at Chichén Itzá had windows
  placed for observations of Venus

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More Ancient Observations

• Polynesians were some of the best observers
• island-to-island sailing navigation
• Chinese incredibly-detailed observations
• For the Emperor son of the heavens
• Accurately predict events to show divineness
• First recorded observations comets, meteor
  showers, meteorites, eclipse predictions,
  supernovae
• Built instruments to conduct these studies

A Traditional Polynesian Navigational Instrument
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More Ancient Observations

• Mesopotamia First comprehensive catalog of the
  night sky circa 750 BC
• Babylonians practice of astrology and astronomy
• Egyptians infatuation with the heavens
• First Recorded Sundials ? Obelisks
• 3500 BC seasons, day clock
• Pyramids
• 2680 BC Great Pyramid at Giza completed

Obelisk Karnak Temple
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Jewish and Christian Traditions

• The Bibles Old and New Testaments contain
  numerous astronomical references
• The Jewish Bible, or Old Testament, refers to
  stars, constellations, eclipses
• The Christian New Testament also has several
  astronomical references
• Example the Star of Bethlehem, denoting the
  birth of Jesus

Adoration of The Magi Giotto
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Ancient Greek and Islamic Astronomy and Science
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The Greeks
Farnese Atlas 2nd Century AD Believed to be based
on Hipparchus

• Credited with development of scientific
  principles, starting around 500 BC
• Alexandria, Egypt was a great library and
  research center that opened around 300 BC
• Eratosthenes determined Earths circumference by
  measuring the Suns shadow at two points on Earth
  around 240 BC
• Hipparchus developed a stellar brightness
  magnitude scale

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Islamic Contributions

• 8th and 9th Centuries AD
• Kept and translated historical records
• Developed Algebra
• New instruments and techniques
• Developed many constellation star names
• Examples Aldebaran, Algol (Al the)
• The researchers were not only Muslims, included
  Jews and Christians also worked with Hindus

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The WandersThe Planets
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Observing The Planets

• Planet from the Greek planete wanderer
• Known planets Mercury, Venus, Mars, Jupiter, and
  Saturn (and Earth, of course!)
• Mercury and Venus stayed close to the Sun
• Mars, Jupiter and Saturn could be tracked as they
  moved across the sky

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Early Solar System Notions

• All the known planets moved against the
  background stars
• Occasionally the planets move backwards against
  the stars retrograde
• How could this retrograde occur if Earth was the
  center of the Solar System and even the Universe?
• Thus, the planets presented problems

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The Geometric or Ptolemaic System

• Nearly everyone placed Earth as the center of the
  Universe
• Everything went around Earth Geocentric
• Claudius Ptolemy ancient Greek astronomer and
  philosopher 100-170 AD
• Placed stellar universe on a crystal sphere
• Earth stood still (didnt rotate) Sun orbited
  Earth
• Used looping small circles on the orbits to
  account for the retrograde of the planets
• Ingenious system accepted as Law except a
  Geocentric Universe was wrong!

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Ptolemy

• Even though Ptolemy was Greek, he was born in
  Egypt
• All his observations were done from Alexandria,
  Egypt
• Also a geographer and mathematician
• His Almagest is one of the longest-used
  textbooks!

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Why Do We See Retrograde?

• Each planet orbits the Sun at a different
  velocity
• The closer the planet to the Sun, the faster it
  orbits
• Earth catches up then passes planets further away
  from the Sun, giving the illusion that the planet
  is moving backwards
• The planet does retrograde, but due to the two
  bodies orbital motions

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The Correct Solution

• Would ultimately come nearly 1,500 years later
• However the Geocentric Solar System was deemed
  Scientific Law and in some cases Church Law
• No one could challenge the Geocentric Solar
  System until overwhelming evidence made accepting
  it impossible

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The Birth of Modern Astronomy
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The Copernican Revolution!

• This Revolution was based on the works of four
  men Copernicus, Brahe, Kepler, and Galileo
• Nicolaus Copernicus, a Polish astronomer,
  believed there were too many errors in the
  Ptolemaic Geocentric Universe
• Ptolemys retrograde was too complicated
• So Copernicus developed a Sun-Centered Solar
  System Heliocentric

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Copernicus

• Studied math and optics in college as well as
  Canon (Church) Law
• His work was released late because he was a
  perfectionist
• For relaxation he painted and translated Greek
  poetry into Latin!

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Observations of Motion

• Tycho Brahe made numerous measurements of the
  positions of astronomical objects until his death
  in 1601
• Measurements were accurate to better than 1/100
  of a degree!
• Johannes Kepler Tychos assistant
• Kepler tried to get Tychos data to fit the
  Copernican Heliocentric Solar System Model
• Data did not exactly work for a Heliocentric
  Solar System! So Kepler looked for a new model

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Tycho the Man

• Lost his nose in a sword fight!
• Replaced it with a silver beak
• Rumored he died of bladder complications
• Refused to go out of courtesy after a long
  wine-drinking bout but couldnt go later!

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And what about Johannes?

• Rumor is that Tycho really didnt like Kepler
• Keplers mother was once charged with witchcraft
  Kepler successfully defended her
• Keplers worst subject in college?
• Astronomy!

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Keplers Laws

• Remember Keplers difficulties fitting Tychos
  data to the Heliocentric Solar System?
• Kepler found the orbits of the planets were not
  circles, leading to three Laws
• Keplers 1st Law the paths of the planets around
  the Sun are ellipses, with the Sun at one focus
• Keplers 2nd Law A planet moves so that its
  radius vector sweeps out equal areas in equal
  times

Foci
Circular Orbit
Elliptical Orbit
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Time A
Area A
Area B
Time B
Area A Area B
Time A Time B
Perihelion Closest point to the Sun Aphelion
Farthest point from the Sun
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Keplers Laws

• Keplers 3rd Law The ratio between the square of
  the time needed by a planet to make a revolution
  around the Sun and the cube of its average
  distance from the Sun is the same for all of the
  planets
• (Period of planet)2
• (Average Orbit Radius)3

K (same for all planets)
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Galileo Galilei

• First used the telescope astronomically in 1609
• Sunspots blemishes
• Saw features on the Moon
• Mare
• Mercury and Venus showed phases
• This meant Mercury and Venus orbits the Sun
  between Earth and the Sun!
• Jupiter had four moons
• Hard to have moons in a Ptolemaic system!
• Saturn had ears
• Milky Way had countless stars

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The Mathematical Finish!
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Newtons 1st Law of Motion

• An object remains at rest or in motion at a
  constant velocity unless acted upon by an outside
  force

Good is the Force!

• What is a Force?
• Any influence that can change the speed or
  direction of motion of an object

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Newtons 2nd Law of Motion

• A relationship between acceleration of an object,
  force placed on the object, and the objects mass

force (mass) (acceleration)
f ma
Units f kg-m/s-s Newton (N)
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Weight is a Force

• An objects weight is the force with which the
  object is attracted by a bodys gravitational pull

f ma
w mg
A car has a mass of 1,500 kg. What is its weight?
w mg
w (1,500 kg) (9.8 m/s-s) 14,700 N
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Newtons 3rd Law of Motion

• When one object exerts a force on a second
  object, the second object exerts an equal force
  in the opposite direction on the first object
• Sometimes called the Action Reaction law
• Rocket blasting off action is force of the
  combustion/flame, reaction is the rocket moving
  in the opposite direction of the flame
• A book pushes against a table (a force), the
  table pushes back (opposite and equal force)

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Circular Motion

• Centripetal Force, Fc inward force on an object
  moving that object in a curved path

m
v
m v2 r
Fc
Fc
r
Fc centripetal force
m objects mass
v objects velocity
r radius of the circular path
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Newtons Universal Law of Gravity

• Every object in the universe attracts every other
  object with a force proportional to both of their
  masses and inversely proportional to the square
  of the distance between them

F Gravitational force
G Gravitational Constant
Gm1m2 R2
F
m1 first objects mass
m2 second objects mass
R distance between the two objects
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Sir Isaac Newton

• In addition to his Laws, he is responsible for
• Newtonian reflector telescope
• Prism / spectrum
• Binomial theorem of Algebra
• Invented Calculus!
• All before the age of 23

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Im An AriesAstrologically-Speaking
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Astronomy versus Astrology

• Historically Astronomy Astrology went
  hand-in-hand
• Astronomy scientific examination of the Universe
• Astrology predict ones future due to the
  positions of specific celestial bodies
• The premise celestial objects affect us here on
  Earth
• The question what scientific evidence backs
  astrology?

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Astrology

• Do celestial objects affect us here on Earth?
• Yes!
• Sun and seasons, daylight
• Moon and tides
• Impactors (asteroids, comets)
• What does astrology claim?
• Through unknown forces the arrangement of
  celestial objects can determine human
  characteristics and fates

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Bad Astrology

• Astrology today is based primarily on the
  influence of the planets on individual lives
• Yet the planets are so far away that their
  gravitational influence is nil
• Example Jupiters gravitational influence on
  Earth raises our tides 0.0001 inch!
• Why not include closer-by asteroids?
• Why do astrologers now include Uranus, Neptune
  and Pluto when they were not included prior to
  their discovery??
• Pluto? Planet or ???

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Sun-Sign Astrology

• The most-popular form this is based on the
  Suns position in the sky relative to background
  stars
• Your Sign? Capricorn, Aquarius, Leo, Sagittarius,
  Ophiuchus (Ophiuchus ??)
• Astrologers claim you are born under the sign in
  which the Sun is in that constellation
• However the Sun is not in that constellation due
  to Earths precession!

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