1. Planet Earth Earth’s Cycles

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

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

4. Direction of Rotation A B
If you are looking down at the North Pole, does the earth spin
Counterclockwise
Clockwise

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

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

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

8. Milankovitch Cycles
These three cycles, in combination, can alter climate
Eccentricity
Obliquity
Precession
Milankovitch 2.38 min

9. Questions?

10. 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

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

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

13. The Moon Formation of the moon NoMoon (2.14 min)
Before 1969, hypotheses why Earth had such a large satellite
Fission Hypothesis
Capture Hypothesis
Co-Formation Hypothesis
Giant Impact Hypothesis
NoMoon (2.14 min)

14. The Moon Lunar Landings Scale (<2 sec) 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 ~ million years)
Scale (<2 sec)

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)

16. 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

17. Rare Earth Hypothesis Geologic events 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

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 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 ( 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.