atmospheres/ greenhouse effect/ spectroscopy

Charles HakesFort Lewis College 1


Atmospheres/

Greenhouse Effect/

Spectroscopy


Logistics

• Midterm grades will be posted by Monday (faculty.fortlewis.edu/hakes_c)

• Review• Atmospheres• Planet Temperatures• Spectroscopy• Green House Effect

http://faculty.fortlewis.edu/hakes_c


Distance to Mercury

• Look up distance from Sun (A.U.) in appendix…

• Need eccentricity of Mercury. (Then check page 32.)


Seti@home Notes

• Credit is available if you join!• link is on my home page

• download the software• install and run - you will have to “connect” to the SETI

project after you install• after completing a work unit, join the FLC group • email me for credit

• (Keep running it if you want to keep the credit.)


Review

• What was the most important thing you learned?• Albedo is how much light gets reflected. • Earth has an albedo of 0.3• Albedo is not related to libido.• For any given temperature, the lighter

stuff moves faster.• Wien’s law:


Blackbody Radiation (Review!)

• 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.


Figure 2.10Blackbody Curves

• Note the logarithmic temperature scale.• For linear scale, go look at the “blackbody” section of: http://solarsystem.colorado.edu/

http://solarsystem.colorado.edu/



Wien’s Law

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


You observe E-M radiation emitted from a warm dense object. The most radiation

appears to be emitted at 5.8x10-4 cm. What temperature is the object?

A) 400 K

B) 500 K

C) 600 K

D) 700 K


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.



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.




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


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.


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


Earth’s Atmosphere

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


Which will have the greatest effect on a planet’s temperature?

A) doubling a planet’s distance to the sun

B) doubling a planet’s albedo

C) doubling a planet’s mass

D) doubling a planet’s rotation rate


Compared to Earth, the Moon undergoes temperature extremes because?

A) It orbits the Earth, and therefore gets both closer and farther from the Sun than Earth

B) It has no atmosphere

C) It rotates very slowly

D) Both B and C


Planet Temperatures

• Go to Solar System Collaboratory to see planet temperatures page.

• Look at fact sheet• Earth - (albedo 0.3) 288 K• Moon - (albedo 0.07) 280 K• Mars - (albedo 0.2) 218 K• Venus - (albedo 0.8) 730 K

• Compare model to fact sheet.• Review model - distance and albedo.



Planet Temperatures

• Compare the model to the fact sheet.• Earth - (albedo 0.3) 288 K (model 255 K)• Moon - (albedo 0.07) 280 K (model 273 K)• Mars - (albedo 0.2) 218 K (model 214 K) • Venus - (albedo 0.8) 730 K (model 219 K)

• Model with fast-rotating planet with variable albedo predicted temperatures that were too low.

• Something is missing from the model…


What is Missing from the model?

A) Realistic rotation rates for the planets

B) Geothermal Energy

C) Distance from the Sun

D) Something else important


Greenhouse Effect

• Exhale


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

A) True

B) False


Greenhouse Effect

• Visible light comes in though the atmosphere and heats the ground.

• Re-radiating infrared light can’t get out because the atmosphere is partially opaque.

• Greenhouse gasses must have at least 3 atoms in each molecule to absorb effectively in the IR.

• Note - “real” greenhouses merely stop convection from carrying away heat.


Figure 2.8Electromagnetic Spectrum


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


Greenhouse “Strength” Contributors

• Total atmospheric pressure• Greenhouse gas percent• Greenhouse gas effectiveness


Add Greenhouse “Strength” to Model

• Earth - 0.65• Mars - 0.077• Venus - 121.0


Planet Temperatures

• Compare the model to the fact sheet.• Earth - (A 0.3, GH 0.65) 288 K (model 289 K)• Moon - (albedo 0.07) 280 K (model 274 K)• Mars - (albedo 0.2) 218 K (model 218 K) • Venus - (albedo 0.8) 730 K (model 730 K)


Planet Temperatures

• Compare the model to the fact sheet.• Earth - (A 0.3, GH 0.65) 288 K (model 289 K)• Moon - (albedo 0.07) 280 K (model 274 K)• Mars - (albedo 0.2) 218 K (model 218 K) • Venus - (albedo 0.8) 730 K (model 730 K)

• Much better agreement!


Greenhouse Runaway

• On Venus, the temperature was just high enough to keep most of the water in the atmosphere.

• CO2 could not be absorbed into the water, and eventually trapped in the surface rocks.

• If all Earth’s CO2 were released into the atmosphere, it would be ~98% CO2, 2% N2 and the pressure would be ~70x current.


Figure 6.8Venus, Up Close


Figure 6.30Venus’s Atmosphere


Discovery 5-2aThe Greenhouse Effect and Global Warming


Discovery 5-2bThe Greenhouse Effect and Global Warming


What gas is the most significant contributor to Earth’s greenhouse effect?

A) Methane

B) Water vapor

C) Carbon monoxide

D) Carbon dioxide


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?

atmospheres/ greenhouse effect/ spectroscopy

Documents