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Fort Lewis College
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Blackbodies
Atmospheres
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Fort Lewis College
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Outline
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Review
Kinetic Energy/Temperature
Blackbodies
Atmospheres
Green House Effect
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Fort Lewis College
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Tutor (Shane)
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Thursday 5-6 (or longer if needed)
BH640
Register clickers…
Homework…
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Fort Lewis College
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Review
• What was the most important thing
you learned?
• There are charged particles bouncing back and
forth on the (field lines in the) magnetosphere
• Aurora… “excited” molecules (or atoms) being
“bumped” in the atmosphere
• Temperature is a measure of the average
kinetic energy of a body’s molecules.
Ek = 1/2Mv2
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Fort Lewis College
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Review
• What was the most important
thing you learned?
• The solar wind is NOT the only reason
Mars has no atmosphere.
• The magnetosphere of Jupiter is the
largest object in the solar system.
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Fort Lewis College
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Tornado
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Fort Lewis College
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Tornado
• Tornado photo courtesy of Gary Gianniny
and email from Scott White.
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Fort Lewis College
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Which temperature will freeze water?
A) 65° F
B) 5° C
C) 263 K
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Fort Lewis College
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Temperature
• Temperature is just a measure of the
average kinetic energy of a body’s
molecules.
• Go to Solar System Collaboratory to see
temperature scales.
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Fort Lewis College
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More Precisely 2-1
The Kelvin Temperature Scale
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Fort Lewis College
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Temperature
• With enough kinetic energy
(temperature), molecules can
“escape” from a planet.
• http://www.xkcd.com/681/
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Fort Lewis College
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Small Group Exercise
• Normal Human body temperature is 37 °
C.
• What is this temperature in Kelvins?
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Fort Lewis College
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Heat Transfer
• Conduction
• Transfer from one mass to another mass that is touching.
• Convection
• Transfer though a gas (air) that moves across a mass
• Radiation
• Transfer using electromagnetic radiation
• This is the least efficient method
• This is the only method available in/through space
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Fort Lewis College
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Albedo
• Albedo - the fraction of light that is reflected
from a planet (or other solar system body).
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A unitless number from 0 to 1.
0 - all light is absorbed (very black)
1 - all light is reflected (very white)
Earth's average albedo is 0.30, so 30% of the
sunlight is reflected.
• The light absorbed would be one minus the
albedo. For the Earth, 1.00-0.30=0.70, so 70%
of the light is absorbed.
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Fort Lewis College
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Blackbody Radiation
• “Blackbodies” are not black.
• Blackbody Radiation is from an
“ideal” object with albedo = 0.
• Any dense, warm, object can be
approximated as a “blackbody”.
• The “peak” of the radiation “curve” is
related to the temperature of the
radiator.
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Fort Lewis College
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Figure 2.9
Ideal Blackbody Curve
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Fort Lewis College
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Radiation
• Higher temperature bodies radiate energy
in shorter wavelength radiation.
• The Sun radiates at visible wavelengths
• The Earth (and other planets) radiate at
much longer wavelengths.
• Go to Solar System Collaboratory to see
black body page.
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Fort Lewis College
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Figure 2.10
Blackbody Curves
• Note the logarithmic
temperature scale.
• For linear scale, go
look at the “black body”
section of:
http://solarsystem.colora
do.edu/
• example - oven
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Fort Lewis College
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Wein’s Law
• The “peak” frequency of the radiation
“curve” is directly proportional to the
temperature of the radiator.
lmax =
Charles Hakes
Fort Lewis College
0.29 (cm K)
T (K)
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Small Group Exercise
• Normal Human body temperature is 37 °
C.
• What is this temperature
0.29 (cm in
K)Kelvins?
lmax =
T (K)
• What is the peak wavelength emitted by a
person at this temperature?
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Fort Lewis College
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Figure 2.8
Electromagnetic Spectrum
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Fort Lewis College
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What is the peak wavelength emitted
by an object with temperature 6,000 K?
A) 4.8x10-5 cm
B) 4.8x10-4 cm
C) 2.9x10-5 cm
D) 2.9x10-4 cm
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Fort Lewis College
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Planet Temperature
• Go to Solar System Collaboratory on EVM
“physics” page.
• A planet must balance absorbed light and radiated
light to get a temperature.
• Light intensity decreases with distance. (another
1/r2 law)
• Farther from the sun, the absorbed light is less.
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Fort Lewis College
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Planet Temperature
• Go to Solar System Collaboratory on EVM
“physics” page.
• A planet must balance absorbed light and radiated
light to get a temperature.
• Light intensity decreases with distance. (another
1/r2 law)
• Farther from the sun, the absorbed light is less.
• Go to Solar System Collaboratory on planet
temperature page.
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Fort Lewis College
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Figure 5.7
About 30% of the sunlight hitting the Earth is reflected
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Fort Lewis College
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To Atmosphere or Not
• Once you know a planet’s temperature you can
see if it will have an atmosphere, and how that
atmosphere can affect a planet’s temperature.
• Compare kinetic energy of molecules with
“escape velocity” from the planet.
• Light molecules (of a given temperature T) move
faster than heavy molecules of the same
temperature.
• A small fraction will always escape.
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Fort Lewis College
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To Atmosphere or Not
• Primary atmosphere
• What a planet had after formation
• Mostly H, He - almost all gone from the
terrestrial planets (never really was here)
• Secondary atmosphere
• Heavier molecules N2, CO2 From rock
outgassing
• H2O from outgassing and comet impacts.
• O2 from Life
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Fort Lewis College
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Earth’s Atmosphere
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78% nitrogen
21% oxygen - this is from living organisms
Plus Ar, CO2, H2O.
Note layers
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Fort Lewis College
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Figure 5.5
Earth’s Atmosphere
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Fort Lewis College
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Meteorology
• Science dealing with phenomena in the
atmosphere (Not the study of meteors)
• Warm air rises and expands
• Cold air sinks and shrinks
• Must conserve linear and angular momentum.
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Fort Lewis College
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Figure 5.6
Convection
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Fort Lewis College
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Removing all greenhouse gasses from
the Earth’s atmosphere would be good
A) True
B) False
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Fort Lewis College
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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Fort Lewis College
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