The Changing View from Earth

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.html

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/SolarMotion/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 • 6,000۫ 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