Charles Hakes Fort Lewis College1. Charles Hakes Fort Lewis College2 Black Bodies/ Atmospheres

Charles HakesFort Lewis College 1

Charles HakesFort Lewis College 2

Black Bodies/

Atmospheres/

Charles HakesFort Lewis College 3

Outline

• Remove “checked” items from folder.• Review• Interiors/Magnetospheres• Kinetic Energy/Temperature• Atmospheres

Charles HakesFort Lewis College 4

Logistics

• Test 2 - Week from Wednesday• Review• Blackbodies• Atmospheres• Green House Effect

Charles HakesFort Lewis College 5

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. (?)

Charles HakesFort Lewis College 6

Which is colder?

A) 100° C

B) 200° F

C) 300° K

Charles HakesFort Lewis College 7

Temperature

• Temperature is just a measure of the average kinetic energy of a body’s molecules.

Charles HakesFort Lewis College 8

Tornado

Charles HakesFort Lewis College 9

Tornado

• Tornado photo courtesy of Gary Gianniny and email from Scott White.

Charles HakesFort Lewis College 10

Which temperature will freeze water?

A) 65° F

B) 5° C

C) 263 K

Charles HakesFort Lewis College 11

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.

Charles HakesFort Lewis College 12

More Precisely 2-1The Kelvin Temperature Scale

Charles HakesFort Lewis College 13

Temperature

• With enough kinetic energy (temperature), molecules can “escape” from a planet.

• http://www.xkcd.com/681/

Charles HakesFort Lewis College 14

Small Group Exercise

• Normal Human body temperature is 37 ° C.

• What is this temperature in Kelvins?

Charles HakesFort Lewis College 15

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

Charles HakesFort Lewis College 16

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.

Charles HakesFort Lewis College 17

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.

Charles HakesFort Lewis College 18

Figure 2.9Ideal Blackbody Curve

Charles HakesFort Lewis College 19

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.

Charles HakesFort Lewis College 20

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

Charles HakesFort Lewis College 21

Wein’s Law

• The “peak” frequency of the radiation “curve” is directly proportional to the temperature of the radiator.

Charles HakesFort Lewis College 22

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?

Charles HakesFort Lewis College 23

Figure 2.8Electromagnetic Spectrum

Charles HakesFort Lewis College 24

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

Charles HakesFort Lewis College 25

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.

Charles HakesFort Lewis College 26

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.

Charles HakesFort Lewis College 27

Figure 5.7About 30% of the sunlight hitting the Earth is reflected

Charles HakesFort Lewis College 28

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.

Charles HakesFort Lewis College 29

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

Charles HakesFort Lewis College 30

Earth’s Atmosphere

• 78% nitrogen• 21% oxygen - this is from living organisms• Plus Ar, CO2, H2O.• Note layers

Charles HakesFort Lewis College 31

Figure 5.5Earth’s Atmosphere

Charles HakesFort Lewis College 32

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.

Charles HakesFort Lewis College 33

Figure 5.6Convection

Charles HakesFort Lewis College 34

Removing all greenhouse gasses from the Earth’s atmosphere would be good

A) True

B) False

Charles HakesFort Lewis College 35

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?