1. Celestial Motion:
History and Earth

2. Ptolemy Copernicus Galileo
OUTCOME QUESTION(S):
S1-4-04:
What evidence is there that the sun is the centre of our solar system?
S1-4-05:
How does the position and motion of Earth produce day/night, the phases of the moon, and the seasons?
Vocabulary & People 
Ptolemy Copernicus Galileo
Kepler Retrograde Geocentric Heliocentric Solstice Equinox

3. Planet is Greek for “wanderer”
Ptolemy (100 AD)
Summarized naked-eye observations and
knowledge of that time
Earth was centre of the universe - Geocentric
In good with the Church
Planet is Greek for “wanderer”
Observation:
Some planets seem to move backwards in orbits:
“Retrograde motion”

4. Ptolemy’s proposed mini-loops were called “epicycles”
GEOCENTRIC
Ptolemy
Ptolemy’s proposed mini-loops were called “epicycles”

5. Called the “Founder of modern astronomy”
Copernicus (1473)
Produced mathematical evidence for a Sun-
centered system – heliocentric
Easily explained retrograde motion
Proved Earth rotated on its axis once daily and
revolved around the sun once yearly
Not in good with Church
Called the “Founder of modern astronomy”

6. HELIOCENTRIC
Copernicus

7. What can we see now?

8. The first one was a simple refracting telescope
First optical telescope made in Netherlands (1608):
Uses curved optical elements
Gathers and collects light to a focal point
Increase apparent size and apparent brightness
The first one was a simple refracting telescope

9. Different energies provide astronomers with different information
a Refracting telescope - lenses focus an image
b Reflecting telescope - mirrors focus an image
Telescopes are classified by the energy detected:
Optical – visible light
Infrared – heat energy
Ultraviolet, X-ray
Different energies provide astronomers with different information

10. Galileo (1564)
Perfected the telescope (built a few years earlier)
First to state and use the scientific method
Discovered moons around Jupiter
1 Proof that not all objects traveled around Earth
Venus had phases (day/night) like Earth
2 Proof that it traveled around the Sun
Not in good with the Church

11. Galileo’s drawings and scientific records of his observations

12. Galileo published his book confirming Copernicus’ mathematics, and was accused of heresy by the Church.
Would not recant his work as a mistake and spent life under house arrest
By the way, Pope John Paul II made a public apology and exonerated Galileo in 1992

13. Brahe’s goal was to prove Copernicus incorrect
Kepler (1571)
Worked as assistant for astronomer, Tycho Brahe
Brahe’s goal was to prove Copernicus incorrect
Brahe built one of the best
observatories in the world
He received loads of money from the Church in hopes he could prove the Earth-centred view…he failed
Measured positions of 777 stars and five planets that were known at that time

14. Kepler used Brahe’s data after his death to describe three laws of planetary motion:
1. Planets orbit the Sun in ellipses
2. Planets move faster close to Sun, and slower
farther away
3. Planets farther away have a longer orbit

15. Earth rotates towards the East
The Earth rotates on its axis once a day.
At any time - half of Earth is in “day” and half in “night.”
Earth rotates towards the East
winter
summer
The Earth revolves around the Sun once a year.
At any time - half of Earth is in “winter” and half in “summer.”

16. Time-lapse photography to show the stars spinning as we rotate on our axis

17. Our axis is tilted at 23.5o (degrees)
This tilt and the curvature of the Earth is responsible for the variations in the Sun’s energy – and creates our seasons.

18. Summer Solstice (June 21)
Summer: not only more “direct” but also more hours of the Sun’s energy
Spring Equinox
(Mar 21)
12h and 12h
Winter
“indirect” energy
Winter Solstice
(Dec 21)
Shortest Day
Summer Solstice (June 21)
Longest Day
Fall Equinox
(Sept 22)
12h and 12h
Summer
“direct” energy

19. What do you notice?

20. That’s why there is a “dark side” of the Moon
Moon Rotation
Moon completes 1 rotation on its axis in the same time as it completes 1 revolution around the Earth (synchronous)
We always see the same side facing the Earth
That’s why there is a “dark side” of the Moon
Orbit is elliptical
Tilted 5°
Mean Distance: 384,400 km

21. Phases of the Moon
Shines only by reflected sunlight
Depends on fraction of sunlit half visible to us

23. CAN YOU ANSWER THESE QUESTIONS? S1-4-04:
What evidence is there that the sun is the centre of our solar system?
S1-4-05:
How does the position and motion of Earth produce day/night, the phases of the moon, and the seasons?
Vocabulary & People 
Ptolemy Copernicus Galileo
Kepler Retrograde Geocentric Heliocentric Solstice Equinox