HISTORY OF
ASTRONOMY
Section 10.1 – Early Models of the Universe
E V E RY S T O RY H A S A
BEGINNING….
If I have seen further, it is by
standing on the shoulders of
giants.
-
Sir Isaac Newton (1642 – 1726)
THE GREEKS:ARISTOTLE,
PTOLEMY AND GEOCENTRISM
A R I S T O T L E ( 3 8 3 – 3 2 2 B. C. )
 A famous Greek philosopher, one of the first
people to leave a written record of their thoughts about
the solar system.
 His observations were made with the naked eye.
This included the sun, the moon, the stars, and the
planets. It would be almost two thousand years before
telescopes would be invented!
A R I S T O T L E ( 3 8 3 – 3 2 2 B. C. )
 Important contributions:
1. The earth is a sphere. Aristotle
observed a curved shadow on the
moon and figured the earth must be
casting the shadow.
A R I S T O T L E ( 3 8 3 – 3 2 2 B. C. )
Important contributions:
2. He placed the earth at the centre
of the universe because patterns in
the stars did not seem to change.
This resulted in the geocentric
model of the universe defined
below.
GEOCENTRIC MODEL
 A model of the universe
 DRAW MODEL ON
that places earth at the centre
BOARD
with the Sun, moon, planets
and stars revolving around
the earth.
GEOCENTRIC MODEL
 The geocentric could not
account for the apparent
movement of the planets. For
example, Mars seemed to change
directions in a looping pattern
which could not happen in
Aristotle’s model.
PTOLEMY (83 – 168 A.D.)
 Ptolemy attempted to
explain the movement of
planets by adjusting
Aristotle’s model and making
it more complicated!
PTOLEMY (83 – 168 A.D.)
Important contribution:
1. Suggested that planets
move in epicycles as they
orbit the earth.
(DRAW DIAGRAM)
NICHOLAS COPERNICUS
 Aristotle and Ptolemy’s model
was accepted for centuries. It wasn’t
until the 1500’s that people including
Nicolas Copernicus began to
challenge the Geocentric Model.
 Copernicus still only had his eyes
to overserve the sky.
H E L I O C E N T R I S M : T H E C O N T ROV E R S Y
Important Contribution:
He explained the motion of the planets by placing the
sun at the centre of the universe. This was called the
heliocentric model.
HELIOCENTRIC MODEL
Heliocentric Model: A model of the universe
that places the Sun at the centre, with the earth and
planets revolving around the sun. This is shown in
the image below:
Unfortunately, Copernicus was unwilling to
present his theories because it went against the
teachings of the church, which supported the
geocentric model. His ideas would have been
treated with persecution and possibly death by
burning at the stake!
Copernicus decided to keep his theories to
himself until he was dying, at which point he
published his ideas in a book.
GALILEO GALILEI (1564 –
1642 A.D.
 https://www.youtube.com/watch?v=NMM8vx9vDiE
A MARTYR IS BORN…ALMOST
Galileo was forced to take back his theories in order to
avoid being burned at the stake.
JOHANNES KEPLER
As Galileo was resting in house arrest, Johannes
Kepler was working to prove Copernicus theory
once and for all.
 https://www.youtube.com/watch?v=a19LTnXkyVQ
KEPLER’S CONTRIBUTIONS
Realized that all planets move in ellipses with the
sun located at one focus.
The time it takes a planet to revolve around the
sun is related to how far away from the sun it is
located. (DRAW ELLIPSE DIAGRAM)
SIR ISAAC NEWTON
Considered to be one of the
most influential scientists to
have ever lived.
Important Contribution:
• Used math to show that gravity
keeps planets in orbit.
TECHNOLOGY
I) Stone Circles
Hardly “technology” by today’s standards. However,
built by the ancient civilizations these were designed
to tell their users about the time of year based on
the position of the moon, sun or stars.
Stonehenge is perhaps the most wellknown example of stone circles. One
theory suggests that they were aligned
so that the sun would rise within a
certain stone configuration only during
the shortest day of the year.
ASTROLABE
 An instrument that was developed
in ancient times (Aristotle and
Ptolemy’s time) and could be used to
measure the height of a celestial
body above the horizon. This lead to
more accurate observations of the
sky.
TELESCOPES
The earliest was used by Galileo and
could only make an object seem 20x closer
Newton invented the reflecting telescope
which greatly improved the strength of
magnification.