1. The Changing View from Earth
Chapter 13

2. Cartoon of the Day

3. What our Ancestors Saw
For thousands of years the sky has been a source of information
Time
Date
Weather
Farmers took their cues from the celestial bodies (Sun, moon, stars) to know when to plant, and harvest their crops

4. Sailors used stars as a guidance system to cross oceans
Astrologers were in demand
People believed their destinies could be foretold by the stars.
Ancients used the stars and motion of planets to
Predict planetary motion, seasons, and eclipses

5. Stories from Cultures Hindu mythology
Seven wise men married seven sisters. Six of the women divorced their husbands and moved to another location in sky. They became the Pleiades (distinct star pattern)
Asterism – a distinctive star pattern
The seven husbands became the seven stars of the big dipper. The wife became Alcor. A star in the crook of the big dipper.

7. Stories from Cultures Algonquin, Iroquois, and Narragansett
saw the constellation Ursa Major as a bear running away from hunters
In the fall because the bear is low enough to brush the trees … the blood from its wounds turns the leaves red.
Another legend tells of 3 hunters chasing 4 elk as the 7 stars of the big dipper.
One hunter is accompanied by a dog

8. Celestial motion (Lunar)
The moon traces a westward path across the sky.
Each night it rises in the east an hour later than the previous night
It’s shape appears to change in phases, waxing from thin crescent to half and full moon. Then waning to a sliver again.

9. Solar Motion
The Sun has no phases
It also rises earlier and farther north each day from December 22 to June 22 and sets later
Through the summer and fall it rises later and set earlier.

10. Stellar Motion Stars and Planets also follow the same pattern
They rise 4 minutes
Earlier each night

11. Planetary Motion And Retrograde
Greeks noticed 5 objects wandering through the stars
Called planets
Mercury, Venus, Mars, Jupiter, Saturn
Venus and Mercury seemed to stay close to the sun
Mars, Jupiter, Saturn wandered Eastward
Once a year they appeared to go backwards (westward)

12. Retrograde motion
Retrograde motion is the backwards motion that planets appear to trace across the sky.

13. Modelling Celestial Motion
Noticing the patterns is only half the battle
Come up with basic ideas or theories
Check theories using models
Two early models
Geocentric
Earth centered model
Heliocentric
Sun centered model ( the one accepted today)

14. Geocentric
Aristotle
Placed stars on outer circle (firmament or fixed stars)
Also called the celestial sphere
Inside the sphere he arranged more concentric spheres on which he placed the Sun, Moons and planets

15. Explaining Epicycles Aristotles model didn’t explain epicycles
Ptolemy created a model which included an additional level of circles called Epicycles
Good for predicting astronomical events

16. Heliocentric 1500’s Nicholas Copernicus Proposed a new model Fixed sun
Planets (including Earth rotate around the sun)
Arranged the planets orbits in a solar plane
Imaginary disk extending out the suns Equator

17. Galileo Italian Astronomer
Discovered evidence supporting heliocentric model.
Used a telescope
Saw that Venus had phases like the moon did
Spots on surface of sun
Mountains on the moon
Rings around saturn
Four moons orbiting Jupiter (actually has 16)

18. Galileo Published his ideas in Dialogue
Galileo was required to recant his heliocentric ideas, which were condemned as "formally heretical";.
He was ordered imprisoned; the sentence was later commuted to house arrest.
His offending Dialogue was banned; and in an action not announced at the trial, publication of any of his works was forbidden, including any he might write in the future.

19. The solution
The answers were discovered by a German mathematician Johannes Kepler
According to calculations predictions would be more accurate if planetary orbits were ellipses (rather than circles)
Ideas strengthened by Newton’s Gravitational laws
All objects in the universe are attracted to one another

20. New Planets In 1781 Uranus was discovered
Later using sun-centered model and Newton’s laws they predicted where another planet should be
Pointed their telescopes in it’s direction and discovered Neptune.
Now knew of 8 planets in total (missing Pluto)

21. Today’s Views
Scientist constructed geocentric model based on observations with unaided eye
When Ideas were challenged a new theory was formulated
This process of formulating new ideas continues even today.
Thanks to technology we now have information on solar system, sun, 9 planets and their moons, meteors, asteroids, comets

22. The Sun Made of Hydrogen gas Diameter 1.4 million km (110 times earth)
Surface is constantly writhing/churning
Solar prominance
Streamers of hot gas that arch into space.
Cooler regions appear darker in color (Sunspots)
Near them violent outbursts/eruptions occur – Solar flares
Solar flares send high energy subatomic particles into space. (creates solar wind which can affect Earths activities)

23. The Sun 330,000 times more massive than earth Three layers
Hydrogen and helium
Three layers
Core – 15,000,000 ۫ C
Photosphere – region of suns light
6,000 ۫ C
Corona
1,000,000 ۫ C
Closest star to the Earth
Because Sun has planets orbiting it scientist predict other stars might have planets orbiting

24. The Planets Inner planets Outer planets Pluto Mercury, Venus, Mars
Called terrestrial planets
Because of their rocky composition
Outer planets
Jupiter, Saturn, Uranus, Neptune
Have a gaseous composition
Pluto
Class all by itself because of strange orbit and tiny size

25. Scale Earth diameter = 12,750 km (1 Earth-Diameter)
Venus = 12,100 km (0.95 Earth-diameter)
Jupiter = 11.2 Earth-Diameter
143,200 km / 12,750 km = 11.2

26. Scale Other scales measured Mass Density
Rotational period (time around sun)
Orbital period

27. Measuring Distance
Distances in astronomy are so immense they are “astonomical”
Scale used = astronomical units (AU)
1 AU = average distance from Earth to sun (149,599,000 km)
Mars distance = 1.5 AU
Why is AU expressed as an average distance?

28. Other Solar System Bodies
Asteroids
Known as minor planets (1m – 100’s of km)
Cere’s 1000 km
Irregular shaped bodies of rock (silicate)
Some cross path of earth (potential Collision)
Comets
Made of dust and ice
Orbit at large distances
Some fall towards the sun (evaporate) form tails
Meteors, and Meteorites
Dust and rock particles that heat up an vaporize in earths atmosphere (shooting stars) - Meteors
Some remain large enough to hit the earth - Meteorites