Starry Monday Today! Science 237 at 8pm(!) Observing 9pm (!!) Topic: Understanding Stars

Meteor Showers – caused by comets RadiantDuration Quadrantids (QUA)Dec. 28-Jan. 7 Lyrids (LYR)Apr Eta AquaridsApr. 21-May 12 Beta TauridsJune 30 Delta Aquarids July Perseids (PER) Aug Draconids Oct Orionids (ORI) Oct TauridsOct.12- Dec 2 Leonids (LEO) Nov Geminids (GEM)Dec. 6-19

Meteors, Meteroids and Meteorites A Meteor is a sudden strike of light in the night sky A Meteoroid is a small asteroid, less than 100 m in diameter A Meteorite is any piece of interplanetary matter that survives the passage through Earth’s atmosphere and lands on Earth’s surface

Meteors and Meteorites Small particles that strike the atmosphere Come from fragments of asteroids, Moon, Mars, comets Strike the earth all the time (“meteorites”) –High speed means lots of energy released on impact

Impact Craters Quebec's Manicouagan Reservoir. Large meteorite landed about 200 million years ago. The lake, 45 miles in diameter, now fills the ring. Barringer Crater, AZ 0.8 mi diameter, 200 yd deep; produced by impact about 25,000 years ago

Tunguska ~30 m body struck Siberia in 1908 Energy equal to that of a 10 Megaton bomb! Detonation above ground; several craters

Frequency of Impact Events

Formation of the Solar System Features to explain: –planets are far apart, not bunched together –orbits of planets are nearly circular –orbits of planets lie mostly in a single plane –directions of revolution of planets about Sun is the same, and is the same as the direction of the Sun's rotation –directions of rotation of planets about their axes is also mostly in the same direction as the Sun's (exceptions: Venus, Uranus, Pluto) –most moons revolve around their planets in the same direction as the rotation of the planets –differentiation between inner (terrestrial) and outer (Jovian) planets –existence and properties of the asteroids –existence and properties of the comets

Formation of the Solar System Condenses from a rotating cloud of gas and dust –Conservation of angular momentum flattens it Dust helps cool the nebula and acts as seeds for the clumping of matter

Formation of Planets Orbiting dust – planitesimals Planitesimals collide Different elements form in different regions due to temperature Asteroids Remaining gas

Structure of the Planets explained Temperature and density of materials drop with distance to sun

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

Features of the Earth & Moon Mass: Earth: 6  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)

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

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

Magnetic field/shield: Motion of Charged Particles Charged particles “trapped” by magnetic fields Origin of the Van Allen radiation belts Protects us!

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 billion years old

The Moon – Far Side Can be seen by satellites only

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

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

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

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

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 –F = G M m / R 2

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!

Moon’s Changing Surface

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

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!)

Impact (“Big Whack”) Theory