Download Planetary Change

Planet Earth
Earth’s Cycles
http://apod.nasa.gov/apod/image/0201/earthrise_apollo8.jpg
Seasons and Sunlight
• What is the solar angle of
incidence for the equator for the
globe on the left?
A. 90°
B. 66.5°
C. 47°
D. 43°
• The globe on the left represents:
A. Summer Solstice
B. Winter Solstice
C. Equinox and cannot tell if
it is the spring or fall
D.
Not enough information
http://www.physicalgeography.net/fundamentals/images/earth_sun_angles.gif
Seasons and Sunlight
• What is the solar angle of
incidence for the equator for the
globe on the right?
A. 90°
B. 66.5°
C. 47°
D. 43°
• The globe on the right represents:
A. Summer Solstice
B. Winter Solstice
C. Equinox and cannot tell if
it is the spring or fall
D.
Not enough information
http://www.physicalgeography.net/fundamentals/images/earth_sun_angles.gif
Direction of Rotation
•
If you are looking
down at the North
Pole, does the earth
spin
A
B
A. Counterclockwise
B. Clockwise
http://www.flutrackers.com/forum/attachment.php?attachmentid=1512&d=1176083504
Eccentricity
• 100,000 year cycle
• Winter in North at
Perihelion, and therefore
shorter than summer
• Low eccentricity of 0.005
• High eccentricity of 0.058
• Mean eccentricity of 0.028
• Present eccentricity 0.017
• Moving towards low
centricity - warming
Perihelion
Aphelion
http://en.wikipedia.org/wiki/File:Eccentricity_half.svg
Obliquity
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•
•
•
•
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Tilt of the Axis
41,000 year cycle
Minimum tilt is 21.1º
Maximum tilt is 24.5º
Currently at 23.5º
Tilt is decreasing cooling
http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png
Precession
• Wobble like a top
• Completes the wobble
every ~21,000 years
• Other “north stars,
Thuban in Draco and
Vega in Lyra
• Top 10 sec
• Both 33 sec
http://stardate.org/images/gallery/d_procession.jpg
Milankovitch Cycles
• These three cycles, in
combination, can alter
climate
– Eccentricity
– Obliquity
– Precession
• Milankovitch 2.38 min
http://www.cgd.ucar.edu/research/highlights/section/milankovitch.jpg
Questions?
Earth/Moon/Sun System
• Milankovitch Cycles –
Eccentricity – Earth’s
distance from the sun
varies, with an average
of 93,000,000 miles
• Johannes Kepler’s 2nd
law of Equal Areas
• Sweep
http://outreach.atnf.csiro.au/education/senior/cosmicengine/images/cosmoimg/kepler2ndlaw.gif
The Moon
• Large Satellite
Hypothesis
– planetary habitability is
enhanced by the
presence of a large
satellite
– axial stability of a
planet also enhances
habitability
http://www.dailyflier.com/astro/earth-mars.JPG
The Moon
• Compare to Mars
– Moons of Mars are so
small, they cannot
form a sphere
Phobos
• Deimos (dread) smaller
and further satellite
• Phobos (fear) larger and
closer satellite
Deimos
http://upload.wikimedia.org/wikipedia/commons/2/23/Mars_Moons_Orbit_distance_flipped.jpeg
http://www.lpi.usra.edu/expmars/activities/phobosFS.gif
http://www.astro.keele.ac.uk/~rdj/planets/images/Deimos-viking1.jpg
The Moon
• Formation of the moon
– Before 1969, hypotheses
why Earth had such a
large satellite
• Fission Hypothesis
• Capture Hypothesis
• Co-Formation
Hypothesis
• Giant Impact Hypothesis
• NoMoon (2.14 min)
http://exoplanet.as.arizona.edu/~lclose/teaching/a202/lect5.html
The Moon
• Lunar Landings
– Returned with moon rocks
– Composition of rocks
similar to surface of Earth
– Best fit hypothesis, Giant
Impact Hypothesis
• Angular Momentum
• Composition of Moon
• Age of Rocks (younger
than Earth by ~100-300
million years)
• Scale (<2 sec)
http://www.fas.org/irp/imint/docs/rst/Sect19/moonsim.jpg
The Moon
• Gravitation pull of Moon
(also pulls land)
• Centrifugal forces –
barycenter is pivotal point
• Centrifugal (17 sec)
• Centrifugal1 (7.27 min)
• Tide (20 sec)
• Tide2 (55 sec)
http://www.lhup.edu/~dsimanek/scenario/tides.htm
Earth/Moon System
• Rotation of the Earth
Moon around the
barycenter (<10 sec)
– Pivot is around the
barycenter and not
through the center of
the Earth
http://library.thinkquest.org/29033/begin/earthsunmoon.htm
Rare Earth Hypothesis
• Astronomical events
– Within galactic habitable
zone
– Supernovae to seed our
system
– Sun the “right” size
– Within solar system’s
habitable zone
– Large gas giants
– Large satellite (Moon)
– Occasional bolides strikes
• Geologic events
– Size of Earth
– Dynamo Earth forms
magnetic poles
• Magnetosphere
–
–
–
–
Plate tectonics
Atmosphere
Lithosphere
Oceans (water terrestrial or
extraterrestrial?)
– Glaciations
Mediocrity Principle
• Intelligent life is common
throughout the universe
because, as Carl Sagan
would say, the universe is
a very big place
• Assumes that the Earth’s
life is a common
occurrence
• Assumes that if life
occurs, then rational life
will form with advanced
technology
• Drake Equation:
– N = N* fp ne fl fi fc fL
•
•
•
•
•
•
•
• N* # of stars in the Milky Way
Galaxy (125-500 billion)
fp fraction of stars that have planets (20 –
50%).
ne # planets/star capable of sustaining life (1
to 5)
fl fraction of planets in ne where life evolves
(0-100%)
fi fraction of fl where intelligent life evolves
(0-100%)
fc is the fraction of fi that communicate (10 –
20%
fL fraction of the planet's life during which
the communicating civilizations live
(1/1,000,000th)
N, the number of communicating civilizations
in the galaxy.