Transcript Class2_Earth_in_Space

The Earth in Space
Inner Planets
The Solar System
The Earth-Moon-Sun System
Phases of the Moon
The Moon’s Orbit and
Rotation
The Moon makes 1 rotation per orbit.
Why?
(Solid) Tides
The Moon is pulled into an
oblong shape
So is the Earth,
but to a lesser extent.
Mostly the oceans are affected
Putting on the Brakes on the
Early Moon
Earth pulls on the moon
Slowing it down
Eventually the Moon’s rotation slowed to
once per revolution
Putting on the Brakes
on the Earth
Moon pulls on the Earth’s oceans, which slosh
against the continents. This slows down the Earth.
Our days are getting longer by about 0.016 seconds per century
400 Ma ago, the day was 22 hours long! (400 days/year) (coral)
900 Ma ago, the day was 18 hours long! (486 days/year) (sed rx)
Seasons, Tropics, and Circles
How hot would the Earth be if
there was no atmosphere?
• What is the average temperature of the
moon?
– The moon’s soil is ~252 K, or -21°C on
average (Little et al, 2001, AGU Abstracts)
• (K = °C + 273.15)
Blackbody Radiation
Observation: When something gets hot, it
begins to glow
First, dark red
Then, bright red
Then, yellow
Eventually, blue
Note: This is NOT related to which part of
a flame is hottest
Ultraviolet
Blackbody Radiation
Infrared
Blackbody Radiation
• Maximum Wavelength?
– Wien Displacement Law
 Max (m) = 2898/T
• Total amount of Energy Emitted
– Stefan-Boltzmann Law
– E (W/m2) = 5.7 x 10-8 T4
• T in degrees Kelvin
Blackbody Radiation
• What’s the Point?
– Any body, at any temperature greater than
absolute zero, is emitting light
– Cool objects emit light we can’t see with
our naked eye (in the infrared)
– Emitting light means that the objects are
emitting energy (in the form of light), and
thus are losing energy
So, what temperature should
the Earth be?
• It’s a simple calculation:
– Energy hitting the Earth from the Sun must
equal the energy leaving the Earth
– 1367 W/m2 is hitting the Earth from the Sun
• But 30% of it is reflected back to space
– Albedo = 0.3
• Leaving 973 W/m2 at the Equator
We have to figure out what the AVERAGE amount of light is
hitting the entire Earth
This is the amount hitting the Earth at the Equator (973 W/m2)
Times the area of the EARTH’S DISK (=r2)
Divided by the Earth’s total SURFACE AREA (=4r2)
So, what temperature should
the Earth be?
• It’s a simple calculation:
– Energy hitting the Earth from the Sun must
equal the energy leaving the Earth
– 1367 W/m2 is hitting the Earth from the Sun
• But 30% (planetary albedo) of it is reflected
back to space, leaving 973 W/m2 at the Equator
• So, there’s an average of 243 W/m2 over the
entire surface
– (5.67 x 10-8 * T4) W/m2 are leaving the
Earth
So, what temperature should
the Earth be?
• The Answer: -18.3°C
– The average temperature of the Earth is really ~
15°C
– The Greenhouse effect is ~33°C [ 15° - (-18°) ]
• 4 Ga ago, the sun was 30% fainter, but the
Earth was warmer
– Equilibrium temperature with faint early sun: 40°C
• A Paradox?
What Impacts Insolation?
• Sunspots
– 11 year cycle
What Impacts Insolation?
• The Eccentricity of the Earth’s Orbit
– 100 ka cycle and a 413 ka cycle
What Impacts Insolation?
• The Tilt of the Earth’s Axis
– 41 ka cycle
Warmer
Summer
Cooler
Summer
What Impacts Insolation?
• The wobble of the Earth’s axis and its
orbit (precession) - 23 ka cycle
26 ka
112 ka
11,500 years ago
What is the impact of changes
in insolation?
• How much of a
difference does 30
W/m2 make?
• -18.99°C to 17.59°C
• A range of 1.4°C
Earth’s Orbit in the News….
Aurorae
http://dotearth.blogs.nytimes.com/2008/11/14/from-above-animated-aurora/?hp
• Aurora Australis (Southern Hemisphere)
• Aurora Borealis (Northern Hemisphere)
The Magnetosphere
• The Earth has a Magnetic Field that
extends into space
The Solar Wind
• The Sun emits charged particles that
spew into space
– The amount of particles increase during
high sunspot activity
– And coronal mass ejections (solar flares)
Contact, the origin of the
aurorae
Aurorae on other planets
• Also
– Mars
– Neptune