1. Topic 4
Motions of the Planets,
Stars, Sun, Earth, & Moon

2. History Of Astronomy

3. 70,000 years old History of Astronomy
Page 1
Astronomy is the oldest science known to man
It’s approximately
_____________________________
70,000 years old
Scientists know the age of Astronomy by finding & studying artifacts left behind by ancient man

4. History of Astronomy Page 1
Some of the oldest artifacts & monuments dedicated to studying astronomy found worldwide

5. History of Astronomy Life was tough 70,000 years ago
Page 1
Life was tough 70,000 years ago
Astronomy must have been important to Ancient Man
Why did Ancient man study the sky thousands of years ago??

6. Why Did Ancient Man Study The Sky?
Survival
Time of Day
Time of Year (Seasons)
Direction (celestial compass)
Recreation
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7. Why Develop Models? Page 1
Models help man study & understand the world around
Models can be mental, mathematical, or physical
Can you name the type of models below:

8. What Were the Earliest Models of the Universe??
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The earliest models regarding the structure of the universe were:
______________________________________
Geocentric Model or
Earth Centered Model

9. Aristotle born in 384 BC and died 322 BC
Who is the Father of the Geocentric Model?
Aristotle born in 384 BC and died 322 BC
He said “All celestial objects revolve around Earth including the Sun”
The Earth is stationary or non moving
This model was used to
explained structure of the “heavens”
and the observed motions of the
known celestial objects
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10. The Geocentric Model Was Good It could explain the motion of most
celestial objects
That why it lasted for over 2,200 years
But the geocentric model was known to be flawed
Page 2

11. Geocentric Model Page 2 According to the Greeks
Designed using only NAKED-EYED observations
No instruments were used to aid them
Model was accurate when explaining some motions but could not explain others
Why?? Because it was fundamentally flawed

12. What motions could the Geocentric Model explain & not account for??
YES
Moon?_______________
YES
Sun? ________________
YES
Stars? _______________ NO
Planets?______________
Specifically the retrograde motions of Planets
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13. So Why did the Geocentric Model Last for so long even though it was wrong?
The Church
Comfortable
Lack of Technology to disprove Geocentric model
No other good theories being developed. Why?
Bubonic plague

14. Retrograde Motion
Page 2
The apparent backward movement of a planet over a period of time
NOT real motion, only observed motion
What accounts for retrograde motion?
Why did they see backward movements of planets?
Why to you think planet Mars was studied the most?
Retrograde motion Video

15. Retrograde Motion Lets see what it looks like
Show video clip from the Universe series & then tell story

16. What causes Retrograde Motion??
This occurs because Earth moves faster in its orbit than the outer planets
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Retrograde Animation in folder
Retrograde motion 1:49
Retrograde Video:
Good for website 6:25

17. Ptolemy (85 A.D A.D.)
Ptolemy modified the geocentric model to account for the retrograde motion of planets (add to bottom of page 2)
The "solution" to retrograde motion came in the form of a mad, but clever idea
Add to bottom of page 2

18. Ptolemaic Geocentric Model
"Epicycles", and the concentric spheres to which they were attached were termed the "Deferents”
Analogy Tea Cup Ride
Add to bottom of page 2

19. Ptolemaic Model
Add to bottom of page 2

20. Claudius Ptolemaeus (Ptolemy)
At first, not widely accepted because scientists thought the model to be too complicated
Although the geocentric model with epicycles did explain the motions of the planets better.
Important in terms of predicting astrology and fate.

21. Introduced to explain retrograde (westward) motion of planets
Epicycles
Introduced to explain retrograde (westward) motion of planets
The Ptolemaic system was considered the “standard model” of the Universe until the Copernican Revolution.

22. Epicycles
Insert Seeds Disk
(SLIDESHOW MODE ONLY)

23. Epicycles Add to bottom of page 2 Animation
Use seeds disk to play animation
(SLIDESHOW MODE ONLY)

24. Epicycles Add to bottom of page 2 Animation
Use seeds disk to play animation
(SLIDESHOW MODE ONLY)

25. Who is the Father of Heliocentric Model
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Nicolaus Copernicus (1473 – 1543)
Father of the Heliocentric Universe (Sun in the Center)
Tell the story & news reference the newspaper article

26. Nicolas Copernicus (1473-1543)
Polish cleric first proposed the heliocentric model
Wrote the book De Revolutionibus and stashed it under his mattress
Proposed all planets including Earth revolve around the Sun
Circular orbits at constant velocities
Copernicus’ model was the best
to date but still had problems
accurately pinpointing the position
of the planets

27. Was the Copernican Model completely correct? Why??
Heliocentric Model
In this model, the is at the center and all the planets, including Earth, revolved around it in CIRCULAR orbits
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Sun
Was the Copernican Model completely correct? Why??

28. Heliocentric Model Was the Copernican Model completely correct? Why??
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Heliocentric Model
Was the Copernican Model completely correct? Why??
No the planet’s orbits are slightly elliptical

29. Copernicus’ new (and correct) explanation for retrograde motion of the planets
Explanation of Retrograde Motion
Retrograde (westward) motion of a planet occurs when the Earth passes the planet.
This made Ptolemy’s epicycles unnecessary.

30. Explain the difference between the geo- and helio-centric
models of the solar system.
Helio-centric
Geo-centric
Earth-
centered
Sun-
centered
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31. The Copernican model was better but it was still slightly wrong b/c it stated the planets revolved around the sun in circular orbits
Until…
Helio-centric
Geo-centric
Earth-
centered
Sun-
centered
Page 2

32. Galileo Galilei (1564 – 1642)
Invented the modern view of science: Transition from a faith-based “science” to an observation-based science.
Greatly improved on the newly invented telescope technology. (But Galileo did NOT invent the telescope!)
Was the first to meticulously report telescope observations of the sky to support the Copernican Model of the Universe.

33. Major Discoveries of Galileo (2)
Surface structures on the moon; first estimates of the height of mountains on the moon

34. Major Discoveries of Galileo
Moons of Jupiter
(4 Galilean moons)
(What he really saw)
Rings of Saturn
(What he really saw)

35. Major Discoveries of Galileo (3)
Sun spots (proving that the sun is not perfect!)

36. Major Discoveries of Galileo (4)
Phases of Venus (including “full Venus”), proving that Venus orbits the sun, not the Earth!

37. Galileo Galilei (1564 – 1642)
His discovers led to propelled forward the ideas of Copernicus and heliocentric model

38. Historical Overview