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					« Looking at the sky, night after night, man no doubt noticed
very early that most of the brilliant dots he could see there
retained their relative position. A triangle in that corner
looked pretty much the same next night, and the night after
that; and the same could be said of most of the figures he
saw. But there were a few dots that moved against the fixed
background of stars. These no doubt provoked great
curiosity, and were the subject of very careful scrutiny. The
ancient greeks dubbed them wanderers, and it is from this
greek term that their modern name comes: Planets. »
             HISTORY of
            ASTRONOMY
• Ancient peoples believed the celestial bodies to be
  linked to gods and spirits.
• They credited the celestial bodies (and their
  movements) to different phenomenons like rain, the
  seasons and tides
• It is generally believed that the first astronomers
  were priests, and their comprehension of the skies
  was seen as divine
• Just imagine looking at the night sky and
  having no idea what you were seeing…….
         STONEHENGE
• Built between 3100-2000
  BC on the plain of Salisbury
  in England, Stonehenge is
  an intriguing astronomical
  site
• The alignment of the
  heelstone with the rising
  sun on summer solstice(the
  21st of June, longest day of
  the year) represents a true
  and precise astronomical
  alignment.
• Like stonehenge, many ancient structures
  have astronomical alignments and probably
  had astronomical and religious functions
Sundials were once the only available
       method for telling time
  Ancient peoples used the stars to determine
direction, they relied on the location of certain
            asterisms for direction
                                Asterisms are small
                                groups of stars that
                                form a distinct shape
                                or pattern
                                Constellations are
                                huge groups of stars
                                (80 or more) , these
                                stars occupy an area
                                in the night sky
Astronomy
becomes a
science……
             Pythagoras
6th Centruy BC



• He believed that the planets were attached to
  crystaline spheres, one sphere for every planet
• Pythagoras is also credited with discovering that
  both the morning and night
  star are actually the planet
  venus!
 Aristotle
• In aristotle’s world, the Earth is situated in the centre of
  the universe (or solar system). He believed Earth to be
  composed of 4 elements: earth, air, water and fire
• Aristotle adopted pythagoras’s model of concentric
  spheres for the planets, but added that the Earth was
  immobile…..he proposed the GEOCENTRIC model!!
• Geocentric = EARTH centered (it’s all about us!)
Geocentric Model
       Claudius Ptolemy
                         (85-165 AD)

• (Greek) mathematicien,
  geographer, et astronomer
• He supported the
  geocentric model, and the
  principle of the movement
  of planets in perfect
  circles.
• Ptolemy’s model was VERY
  complex – it used
  EPICYCLES to describe the
  movements of planets
Ptolemy’s Work
                      Epicycles
(Ptolemy’s theory of planetary movement in the geocentric model)




                                                http://www.astro.
                                                utoronto.ca/~zhu/
                                                ast210/geocentri
                                                c.html
The development of the geocentric model:
           Geocentric = EARTH centered
1. Pythagoras introduced the theory of the planets
   being attached to crystalline spheres

2. The geocentric model was proposed by Aristotle
    using both his own ideas and the work of
    Pythagoras.

3. The geocentric model was further supported by
   Ptolemy who added the idea of epicycles to
   explain planetary motion.
               A popular model…
The geocentric model was popular because it
  allowed people to accurately predict the date, time
  and location that certain celestial bodies would
  rise and set
But…..
Each new phenomenon required more and more
  additions to the geocentric model – the model
  became so complex that it contained 55 interior
  spheres, epicycles and many ‘rules’ ….it simply
  became too complex.
   Next…   the Renaissance
                (XIV to XVII centuries)



Exploration and scientific investigations
  became more and more popular in the
  west. Navigation and the calculation of
  time improved due to increasingly
  precise astronomical observations.
           Copernicus 1473-1543
• Copernicus studied mathematics and astronomy
• During Copernicus’s time, Ptolemy’s geocentric
  model was no longer able to explain all of the
  astronomical phenomena that were being observed.
• In response to the inadequacies of the geocentric
  model, Copernicus devised a HELIOCENTRIC model
  of the solar system placing the sun at the centre of the
  solar system. The heliocentric model also had the
  correct order of the planets.
• Heliocentric = SUN centered
The Heliocentric Model
 Tycho Brahe
  (1546-1601)
Tycho Brahe was a
danish astronomer most
know for his incredibly
precise and very
thorough observations.
Tycho Brahe was
wealthy and eccentric.
He used his money to
build many pieces of
astronomical equipment
which he designed.
Johannes Kepler(1571-1630)
• Kepler worked with Tycho Brahe’s
  observational data
• Using Brahe’s data, Kepler made very precise
  calculations about the orbits of the planets
• Kepler developed 3 rules related to planetary
  motion
• One of these rules explains that the planets
  travel in ELLIPTICAL paths – not circular ones
An ellipse is an ELONGATED circle
Instead of a center, an ellipse has two FOCI
Galileo Galilei (1564-1642)
      Using homemade telescopes,
      Galileo made several
      discoveries in support of the
      heliocentric model of the solar
      System

      •   Sun spots
      •   Craters on the moon
      •   The moons of Jupiter
      •   The rings of Saturn
      •   The phases of Venus
• Galileo’s observations led him to the conclusion that the
  heliocentric model (of Copernicus)was superior to the
  geocentric model establish by Aristotle
    The development of the heliocentric model:

              heliocentric = SUN centered

1. In response to the inadequacies of the geocentric
   model, Copernicus devised a HELIOCENTRIC
   model.

2. Kepler explained that the planets travel in
    ELLIPTICAL paths – not circular ones

3. Galileo developed the telescope and made
    observations that led him to the conclusion that
    the heliocentric model was superior.
.
      Today
• The planets orbit the Sun
• The planetary orbits are ellipses (elongated circles)
• There are 8 classical planets (and three dwarf
  planets including Pluto)

				
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posted:11/17/2012
language:English
pages:25