1. Eclipses, Tides & a big Whack – The Earth-Moon System An Earth-Week Lecture April 16, 2007 Dr. Uwe Trittmann Welcome to

2. Today’s Topics Eclipses, Tides & a big Whack – The Earth-Moon System The Night Sky in April

3. On the Web To learn more about astronomy and physics at Otterbein, please visit –http://www.otterbein.edu/dept/PHYS/weitkamp.a sp (Observatory)http://www.otterbein.edu/dept/PHYS/weitkamp.a sp –http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)http://www.otterbein.edu/dept/PHYS/

4. The Earth-Moon System Earth/Moon radius: ¼ Earth/Moon mass: 1/81 Earth-Moon distance: 384,000 km

5. Features of the Earth & Moon Mass: Earth: 6  10 24 kg Moon: 1/81 Earth’s Radius: Earth: 6400 kmMoon: 1/4 Earth’s ra Density: Earth: 5500 kg/m 3 Moon: 3300 kg/m 3 –5.5 times that of water –About 2 times that of a rock Gravity: Earth: 9.8 m/s 2 Moon: 1/6 Earth’s gravity (about the same as in water)

6. Motion of the Moon Moon shines not by its own light but by reflected light of Sun  Origin of the phases of the moon Moon revolves around the Earth period of revolution = 1 month

7. Phases of the Moon

8. Phases of the Moon (cont’d) Moon rotates around earth in one month Moon rotates around itself in the same time  always shows us the same side!  “dark side of the moon” (not dark at all!)

9. Eclipses One celestial object hidden by other or in the shadow of another Solar eclipse: sun hidden by the moon Lunar eclipse: moon in earth’s shadow (sun hidden from moon by earth) Also: eclipses of Jupiter’s moons, etc. Most spectacular because moon and sun appear to be the same size from earth

10. Solar Eclipses Umbra – region of total shadow Penumbra – region of partial shadow Totality lasts only a few minutes! Why isn’t there a solar eclipse every month?

11. Solar Eclipse

12. Solar Corona – Only seen during Eclipses

13. Inside the Umbra It gets dark Temperatures drop Birds stop singing Nature slows down

14. Annular Eclipse 1 3 2 If the moon just isn’t big enough … (Actually, it appears smaller, since it is further away due its eccentric orbit)

15. Lunar Eclipses Moon moves into earth’s shadow… …and out of it (takes hours!)

17. Partial Eclipse

18. Not an Eclipse ! How do we know?

19. Towards Totality

20. Almost total…

21. Totality Q: Why does the Moon look orange in total lunar eclipses

22. Totality A: Because the sky on Earth is blue. The Earth’s atmosphere’s air molecules filter out red & orange frequencies by scattering them into Earth’s night side. This “rest light” illuminates the Moon (weakly).

23. Question Why isn’t there an eclipse every month ?

24. Tides Daily fluctuations in the ocean levels Two high and two low tides per day A result of the difference in gravitational pull from one side of the Earth to the other

25. The idea behind Tides There are two tidal bulges, i.e. two high tides per day, because: –Moon pulls water towards it on one side –Earth is pulled towards the Moon, away from the water on the other side Force of Moon on water (strong) Force of Moon on Earth (weaker) Force of Moon on “back-water” (much weaker)

26. Spring and Neap Tides Tides especially pronounced when Sun and Moon “work together” Same direction  Spring tide Other direction  Neap tide

27. SANDSTORM LEAVING NORTH AFRICA TOWARDS THE ATLANTIC – CANARY ISLAND. The Surfaces of Earth & Moon

28. GIBRALTAR STRAITS

29. NIGHT ARRIVES BETWEEN EUROPE & AFRICA

30. France Iceland Italy ContinentalPlatform England ÁFRICA Already night time here. Spain Atlantic Ocean Cabo Verde Island Canary Islands Islas de la Madera y Azores

31. RED SEA

32. Earth at night (computer processed – it’s never dark all over the Earth)

38. Grande São Paulo Rio de Janeiro Belo Horizonte Salvador Atlantic Ocean Brazilian Continental Platform. NIGHTFALL IN BRAZIL

39. NIGHTFALL IN USA Q: During which season was this picture taken?

40. NIGHTFALL IN USA A: During summer in the northern hemisphere, because it gets dark later the more north you go!

41. The biggest concentration of lights (from top to bottom) are the cities of Boston, New York, Philadelphia and Washington. MiamiHouston Dallas Chicago Still daylight in California. Puerto Rico Columbus

42. Structure of the Earth Core –Mostly iron and nickel –Inner core solid, outer core liquid Mantle –Mostly basalt, a heavy mineral containing iron and magnesium –Soft; can flow even though it is solid rock Crust –Solid surface layer; “floats” on the mantle Density and temperature both increase with depth

43. Surface Features & Dynamics Continental plates drift apart hot magma comes to surface  Volcanism

44. Earth’s Changing Surface

45. Earth’s Atmosphere 78% Nitrogen, 21% Oxygen, 1% Other Troposphere – region of weather Stratosphere – stable and calm Ionosphere – gases charged by interaction with radiation from space

46. Ozone Layer (O 3 ) Absorbs most UV radiation from the Sun Hole over Antarctic –Chlorofluorocarbons (CFC’s) – released by spray cans, refrigerators

47. Greenhouse Effect Earth absorbs energy from the Sun and heats up Earth re-radiates the absorbed energy in the form of infrared radiation The infrared radiation is absorbed by carbon dioxide and water vapor in the atmosphere

48. Magnetosphere Magnetic north pole about 7° west of geographic north pole Driven by motion of molten metals in core

49. Motion of Charged Particles Charged particles “trapped” by magnetic fields Origin of the Van Allen radiation belts  The Earth’s magnetic field protects us from harmful radiation!

50. Aurora Borealis Charged particles bump into air molecules and excite them Subsequently the molecule falls back into its ground state, giving off radiation  the aurora!

51. Aurora Borealis from Space A cosmic particle shower

52. The Moon: Large-Scale Features “Maria” –Dark areas resembling oceans –Plains of solidified lava –Part of the lunar mantle –About 3.2–3.9 billion years old Highlands (“Terrae”) –Light-colored, resemble continents –The lunar crust –More than 4 million years old

53. The Moon – Far Side Can be seen by satellites only

54. The Mountains of the Moon Especially well visible near the terminator – the borderline between light and shadow

55. Moon from our Observatory I Through 8 inch telescope, 40 mm eyepiece, Sony DSC 717 digital camera, December 31, 2003

56. Moon from our Observatory II Through 8 inch telescope, 40 mm eyepiece, Sony DSC 717 digital camera, December 31, 2003

57. Moon from our Observatory III Through 8 inch telescope, 40 mm eyepiece, Sony DSC 717 digital camera, December 31, 2003

58. The Moon - Touchdown Note the soft edges of the crater  Erosion! Traces of the Apollo lunar rover

59. Structure of the Moon Also consists of crust, mantle and core No hydrosphere, magnetosphere or atmosphere Little seismic action

60. Lunar Craters Old scars from meteoroid impacts Lots of them; all sizes –Copernicus ~ 90 km across –Reinhold ~ 40 km across –Also craters as small as 0.01 mm!

61. (Almost) Catastrophic Impacts Orientale Basin Almost 1000 km diameter A somewhat larger impact body could have destroyed the moon!

62. How They Form

63. Moon’s Changing Surface

64. Ages of the Earth and Moon Determined by radioactive dating –Compare amount of radioactive material with amount of decay product –Useful isotopes: Uranium-238 (half-life 4.5 billion years) Uranium-235 (half-life 0.7 billion years) For shorter time scales, Carbon-14 (5730 years) Oldest surface rocks on Earth (Greenland, Labrador) about 3.9 billion years old –When rocks solidified Lunar highlands: 4.1–4.4 billion years old –Rocks from lunar maria slightly younger, more recently melted Meteorites: 4.5 billion years old –Date to origin of solar system

65. Creation of the Earth-Moon system 1.Sister theory: Earth and Moon formed at same time in the same part of the solar system (but they have different compositions??) 2.Capture theory: Earth captured the Moon as it passed by; need not have the same composition (but gravitational capture is improbable) 3.Daughter or fission: spinning Earth threw off the Moon (but how did it get to be spinning that fast?) 4.Impact theory: large body hits the (molten) Earth and is absorbed; part of Earth's mantle is knocked out. (Plausible: supported by computer simulations; but there's no direct evidence!)

66. Impact (“Big Whack”) Theory 1 2 3 4 5 6

67. Giant Impact Theory A massive object sideswiped Earth 4.5 billion years ago The collision scattered crustal debris that later formed the Moon. New calculations show how big the object would have to have been to strike Earth with sufficient force to generate the volume of debris required to create the Moon. Their computer modeling indicates that such an object must have been at least 2 1/2 to 3 times the mass of Mars.

68. The Night Sky in April Nights still long, but EDT => later observing! Spring constellations are up: Cancer, Leo, Big Dipper Saturn dominates the evening, Jupiter early morning.

69. Today at Noon Sun at meridian, i.e. exactly south

70. 10 PM Typical observing hour, early April Saturn

71. Zenith Big Dipper points to the north pole

72. West Perseus and Auriga with Plejades and the Double Cluster

73. West The Winter Constellations –Orion –Taurus –Canis Major –Gemini –Canis Minor

74. South Spring constellations: –Leo –Hydra –Crater –Sextans

75. East Canes Venatici: –M51 Coma- Virgo Cluster Globular Star Clusters –M3, M5

76. East Virgo and Coma with the Virgo-Coma galaxy cluster

77. Virgo- Coma Cluster Lots of galaxies within a few degrees

78. M87, M88 and M91

79. East –Hercules –Corona Borealis –Bootes Globular Star Clusters: M 3 M 13 M 92

80. M13: Globular Cluster

81. Mark your Calendars! Next Starry Monday: May 7, 2005, 8 (!!!) pm (this is a Monday ) Observing at Prairie Oaks Metro Park: –Friday, April 27, 2007, 8:30 pm –Friday, May 25, 2007, 9:00 pm Web pages: –http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)http://www.otterbein.edu/dept/PHYS/weitkamp.asp –http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)http://www.otterbein.edu/dept/PHYS/

82. Mark your Calendars II Physics Coffee is every Wednesday, 3:30 pm Open to the public, everyone welcome! Location: across the hall, Science 256 Free coffee, cookies, etc.