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 SolsticeB. Winter SolsticeC. Equinox and cannot tell if

it is the spring or fallD. 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 SolsticeB. Winter SolsticeC. Equinox and cannot tell if

it is the spring or fallD. 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. Counterclockwise

B. Clockwise

A B

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

http://en.wikipedia.org/wiki/File:Eccentricity_half.svg

Perihelion

Aphelion

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

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

• 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.jpeghttp://www.lpi.usra.edu/expmars/activities/phobosFS.gifhttp://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 eventsAstronomical events– Within galactic habitable Within galactic habitable

zonezone

– Supernovae to seed our Supernovae to seed our systemsystem

– Sun the “right” sizeSun the “right” size

– Within solar system’s Within solar system’s habitable zonehabitable zone

– Large gas giants Large gas giants

– Large satellite (Moon)Large satellite (Moon)

– Occasional bolides strikesOccasional bolides strikes

• Geologic eventsGeologic events– Size of EarthSize of Earth

– Dynamo Earth forms Dynamo Earth forms magnetic polesmagnetic poles

• MagnetosphereMagnetosphere

– Plate tectonicsPlate tectonics

– Atmosphere Atmosphere

– LithosphereLithosphere

– Oceans (water terrestrial or Oceans (water terrestrial or extraterrestrial?)extraterrestrial?)

– GlaciationsGlaciations

Mediocrity Principle

• Intelligent life is common Intelligent life is common throughout the universe throughout the universe because, as Carl Sagan because, as Carl Sagan would say, the universe is would say, the universe is a very big placea very big place

• Assumes that the Earth’s Assumes that the Earth’s life is a common life is a common occurrenceoccurrence

• Assumes that if life Assumes that if life occurs, then rational life occurs, then rational life will form with advanced will form with advanced technologytechnology

• Drake Equation:Drake Equation:– N = N* fp ne fl fi fc fLN = N* fp ne fl fi fc fL• N*N* # of stars in the Milky Way # of stars in the Milky Way

Galaxy (125-500 billion)Galaxy (125-500 billion)• fpfp fraction of stars that have planets (20 – fraction of stars that have planets (20 –

50%).50%).• nene # planets/star capable of sustaining life (1 # planets/star capable of sustaining life (1

to 5)to 5)• flfl fraction of planets in fraction of planets in nene where life evolves where life evolves

(0-100%)(0-100%)• fifi fraction of fraction of flfl where intelligent life evolves where intelligent life evolves

(0-100%)(0-100%)• fcfc is the fraction of is the fraction of fifi that communicate (10 – that communicate (10 –

20%20%• fLfL fraction of the planet's life during which fraction of the planet's life during which

the communicating civilizations live the communicating civilizations live (1/1,000,000(1/1,000,000thth))

• NN, the number of communicating civilizations , the number of communicating civilizations in the galaxy.in the galaxy.