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Black Bodies/
Atmospheres/
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Outline
• Remove “checked” items from folder.• Review• Interiors/Magnetospheres• Kinetic Energy/Temperature• Atmospheres
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Logistics
• Test 2 - Week from Wednesday• Review• Blackbodies• Atmospheres• Green House Effect
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Lab Notes
• Any outside “extra” lab(s) due this week if you want credit before mid-term!
• You need 40 lab points by mid-term to get full (100%) lab credit. (This is not an issue for most of you.)
• Start outside labs!• Spectroscopy in-class lab next week. (?)
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Which is colder?
A) 100° C
B) 200° F
C) 300° K
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Temperature
• Temperature is just a measure of the average kinetic energy of a body’s molecules.
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Tornado
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Tornado
• Tornado photo courtesy of Gary Gianniny and email from Scott White.
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Which temperature will freeze water?
A) 65° F
B) 5° C
C) 263 K
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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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More Precisely 2-1The Kelvin Temperature Scale
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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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Small Group Exercise
• Normal Human body temperature is 37 ° C.
• What is this temperature in Kelvins?
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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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Albedo
• Albedo - the fraction of light that is reflected from a planet (or other solar system body).• 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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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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Figure 2.9Ideal Blackbody Curve
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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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Figure 2.10Blackbody Curves
• Note the logarithmic temperature scale.• For linear scale, go look at the “black body” section of: http://solarsystem.colorado.edu/• example - oven
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Wein’s Law
• The “peak” frequency of the radiation “curve” is directly proportional to the temperature of the radiator.
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Small Group Exercise
• Normal Human body temperature is 37 ° C.
• What is this temperature in Kelvins?
• What is the peak wavelength emitted by a person at this temperature?
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Figure 2.8Electromagnetic Spectrum
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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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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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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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Figure 5.7About 30% of the sunlight hitting the Earth is reflected
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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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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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Earth’s Atmosphere
• 78% nitrogen• 21% oxygen - this is from living organisms• Plus Ar, CO2, H2O.• Note layers
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Figure 5.5Earth’s Atmosphere
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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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Figure 5.6Convection
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Removing all greenhouse gasses from the Earth’s atmosphere would be good
A) True
B) False
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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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