Transcript Integrative Studies 410 Our Place in the Universe

Starry Monday Today!
• Science 237 at 8pm(!)
• Observing 9pm (!!)
• Topic: Understanding Stars
Meteor Showers –
caused by comets
Radiant
Quadrantids (QUA)
Lyrids (LYR)
Eta Aquarids
Beta Taurids
Delta Aquarids
Perseids (PER)
Draconids
Orionids (ORI)
Taurids
Leonids (LEO)
Geminids (GEM)
Duration
Dec. 28-Jan. 7
Apr. 16-25
Apr. 21-May 12
June 30
July 25-31
Aug. 10-14
Oct. 6-10
Oct. 15-29
Oct.12- Dec 2
Nov. 14-20
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
• Barringer Crater, AZ
0.8 mi diameter, 200
yd deep; produced
by impact about
25,000 years ago
• Quebec's Manicouagan
Reservoir. Large
meteorite landed about
200 million years ago. The
lake, 45 miles in diameter,
now fills the ring.
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:
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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  1024 kg
• Radius: Earth: 6400 km
• Density: Earth: 5500 kg/m3
Moon: 1/81 Earth’s
Moon: 1/4 Earth’s ra
Moon: 3300 kg/m3
– 5.5 times that of water
– About 2 times that of a rock
• Gravity: Earth: 9.8 m/s2
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 (O3)
• 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 / R2
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
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