Planet Earth

1
Planet Earth

• Earths Cycles

http//apod.nasa.gov/apod/image/0201/earthrise_apo
llo8.jpg
2
Seasons and Sunlight

• What is the solar angle of incidence for the
  equator for the globe on the left?
• 90
• 66.5
• 47
• 43

• The globe on the left represents
• Summer Solstice
• Winter Solstice
• Equinox and cannot tell if it is the spring or
  fall
• Not enough information

http//www.physicalgeography.net/fundamentals/imag
es/earth_sun_angles.gif
3
Seasons and Sunlight

• What is the solar angle of incidence for the
  equator for the globe on the right?
• 90
• 66.5
• 47
• 43

• The globe on the right represents
• Summer Solstice
• Winter Solstice
• Equinox and cannot tell if it is the spring or
  fall
• Not enough information

http//www.physicalgeography.net/fundamentals/imag
es/earth_sun_angles.gif
4
Direction of Rotation
A
B

• If you are looking down at the North Pole, does
  the earth spin
• Counterclockwise
• Clockwise

http//www.flutrackers.com/forum/attachment.php?at
tachmentid1512d1176083504
5
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/FileEccentricity_hal
f.svg
6
Obliquity

• 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
7
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.jp
g
8
Milankovitch Cycles

• These three cycles, in combination, can alter
  climate
• Eccentricity
• Obliquity
• Precession
• Milankovitch 2.38 min

http//www.cgd.ucar.edu/research/highlights/sectio
n/milankovitch.jpg
9
Questions?
10
Earth/Moon/Sun System

• Milankovitch Cycles Eccentricity Earths
  distance from the sun varies, with an average of
  93,000,000 miles
• Johannes Keplers 2nd law of Equal Areas
• Sweep

http//outreach.atnf.csiro.au/education/senior/cos
micengine/images/cosmoimg/kepler2ndlaw.gif
11
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
12
The Moon

• Compare to Mars
• Moons of Mars are so small, they cannot form a
  sphere
• Deimos (dread) smaller and further satellite
• Phobos (fear) larger and closer satellite

Phobos
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/Deimo
s-viking1.jpg
13
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/a
202/lect5.html
14
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 (lt2 sec)

http//www.fas.org/irp/imint/docs/rst/Sect19/moons
im.jpg
15
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
16
Earth/Moon System

• Rotation of the Earth Moon around the barycenter
  (lt10 sec)
• Pivot is around the barycenter and not through
  the center of the Earth

http//library.thinkquest.org/29033/begin/earthsun
moon.htm
17
Rare Earth Hypothesis

• Geologic events
• Size of Earth
• Dynamo Earth forms magnetic poles
• Magnetosphere
• Plate tectonics
• Atmosphere
• Lithosphere
• Oceans (water terrestrial or extraterrestrial?)
• Glaciations

• Astronomical events
• Within galactic habitable zone
• Supernovae to seed our system
• Sun the right size
• Within solar systems habitable zone
• Large gas giants
• Large satellite (Moon)
• Occasional bolides strikes

18
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 Earths 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.