contribution and works of Copernicus, Tycho, Kepler, Galileo and Newton

1. 16 CENTURIES
From the time of Claudius Ptolemy to the
time of Nicolaus Copernicus, it was the
Ptolemaic model that was accepted.

2.  Thales (625 - 546 BC) - prediction of the
eclipse of the sun in May 28 585 BC.
 Pythagoras (582 - 500 BC) - considered
the Earth as a globe revolving with the
other planets
 Anaxagoras (500 - 428 BC) - explained
eclipses and believed the moon was part
of Earth

3.  Eudoxus (408 - 355 BC) - first to explain
the movement of planets
 Heraclides (387 - 312 BC) - proposed
the sun is the center of the solar
system;observed Mercury and Venus
 Pytheas (380 - 300 BC) - observed the
Pole Star is not the true pole and that
the moon affects the tides

4. Pre-Copernican Astronomy
The Golden Age of Astronomy

5. Nicolaus
Copernicus

6. Nicolaus Copernicus
(1473 - 1543)
 Polish Canon
 De Revolutionibus Coelestium Orbium
 Heliocentric Model
 Father of Modern Astronomy

7. The Copernican System
 Placed the Sun at the center
 His theory did not predict planetary
positions accurately
 Retained epicycles and deferents
 The Copernican theory was wrong but
the Heliocentric idea was right.

8. Tycho Brahe
(1546-1601)
 Called Tycho, the
man with the golden
nose.
 Studied for law but
went to astronomy
and mathematics
 The Observational
Astronomer

9. Tycho’s Work
 Found errors in the astronomical tables
of the times
 Studied the motion of planets
 in 1572, observed the supernova
(Tycho’s supernova)
 Carefully gathered data about
planetary positions

10. Tycho’s Theory
 Believed earth was stationary
 Rejected the Ptolemaic theory because
of its wrong predictions of positions of
heavenly bodies
 Made the earth the immobile center of
the universe
 Devised new and better instruments
 Hired an assistant, Johannes Kepler

11. Tychonian Model
 Earth is the
immobile center
 The moon orbits
around earth.
 The sun orbits
the Earth!
 Planets orbit
around the sun.

12. Johannes
Kepler

13. Johannes Kepler
(1571-1630)
 Three Laws of Planetary Motion
 His Book: Harmonice Mundi (The
Harmony of the World)

14. Kepler’s Theory
 Abandoned CIRCULAR MOTION
 Instead, he discovered the ELLIPSE as
the orbit of Mars
 Discovered that planets do not move at
constant speed
 In his book, he came within a paragraph
of discovering the law of mutual
gravitation.
 Laws of Planetary Motion

15. The Three Laws of
Planetary Motion
1st Law:
Law of Ellipses
All planets revolve around the Sun in
orbits that are ellipses, and the sun
is located at one of the foci.
2nd Law:
Law of Equal Areas
A line drawn from the planet to the
sun sweeps out over equal areas
in equal intervals of time.
3rd Law:
The square of the yperiod (in earth years) of
Law of Harmona planet is equal to the cube of its average
distance (in astronomical units) to the sun.
T 2 α r 3

16. By now, it is clear the planets
revolve around the sun and
the orbits are not circles but
ellipses. The next question is:
What keeps the planets
moving around the sun?

17. Galileo
Galilei

18. Galileo Galilei
(1564 – 1642)
 Defender of Copernicanism
 Made important discoveries about motion.
 Defended the theory that the Earth moves.
 Earth moves.

19. Galileo Galilei
 Made telescopes & used it for astronomy
 Discovered the moons of Jupiter, the
phases of Venus and the sunspots
 Taught that the Earth moves
 Fell into controversy with the church
authorities
 Believed that the Earth is not the center.

20. Question:
If planets move, what or who keeps them
moving?
PPrriinncciippllee iinn tthhoossee ddaayyss::
QQuuiiddqquuiidd mmoovveett,, aabb aalliioo mmoovveettuurr..
WWhhaatteevveerr iiss mmoovviinngg,, iiss mmoovveedd bbyy aannootthheerr??
SSoo wwhhaatt mmoovveess tthhee ppllaanneettss??

21. Galileo’s Answer:
NNootthhiinngg!!
There is no need for a mover. The planets go
on by themselves. Galileo studied motion and
found that once a body is in motion, it will
tend to continue in that state of motion.
((YYeeaahh iitt ssoouunnddss lliikkee NNeewwttoonn,, wwhhoo llaatteerr
bboorrrroowweedd iitt aanndd mmaaddee iitt hhiiss ffiirrsstt llaaww..))

22. Galileo had explained…
what moves planets
(the red line) is inertia.
The remaining question
is what keeps them in
orbit? Gravitation,
which brings us to
Newton.

23. Isaac Newton

24. Isaac Newton
(1642 - 1727)
 His great work:
Principia Mathematica Philosophiae Naturalis
Mathematical Principles of Natural Philosophy
 Law of Gravitation

25. The Principia

26. For Isaac Newton there
is only one remaining
question…

27. If planets tend to go on
along straight lines, why
do they not fly off into
space?

28. Newton’s Solution
 Any mass (object) exerts a force called
gravitation.
 Gravitation is the property of a mass to
pull other masses to itself.
 Between a chair and table, between
an apple and the earth, between the
sun and the planet there is attraction.

29. Inertia makes a planet move
along a straight line but at the
same time, there is a pull exerted
by the Sun on a planet. The
result is that the planet does not
fly to space nor does it fall to the
sun. The combined motion
becomes the elliptical orbit
around the Sun.

30.  Two motions happen at
the same time.
 The planet tends to fly
off.
 Gravitational force
pulls the planet to the
center.
 Result: the orbital
motion

31. In these 99 years (1543-1642), it has
been established:
 That the sun is the center of the solar
system
 That the Earth moves.
 That planets move in elliptical paths.
 That the orbits are maintained by
inertia and gravitation.

32. Write TRUE if the statement is correct and if False, WRITE the word/s
that makes the statement incorrect and opposite to it is the correct
answer.
Ex if false: Blue -> Red
1. Johannes Kepler believed that the earth is the immobile center.
2. Copernicus heliocentric idea was correct and predicted the
planetary positions accurately.
3. Kepler improved the telescope that brings the discovery of the
different phases of the Venus.
4. Tycho hired Kepler as an assistant.
5. Isaac Newton gives the Law of Planetary Motion.
6. Galileo defend Copernicus heliocentric idea.
7. Eratosthenes was famous for his measuring earth’s diameter.
8. Hipparchus invented the armillary sphere.
9. Ptolemy proposed the spherical universe.
10. Aristarchus was the first to push the idea
of heliocentric system.