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. http://www.astro.wisc.edu/~ dolan/java/MoonPhase.ht ml

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. –http://www.earth.uni.edu/~morgan/ajjar/Solar Motion/solarzenith.html

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  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  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