Post on 27-Mar-2015
Venus Earth Mars
The surface temperature of Venus is around 460 C (890 degrees F ), the hottest average temperature in the Solar System. This is due to a runaway Greenhouse Effect.
The atmosphere of Venus is composed of :97% CO2, 2% N2 and less than 1% of O2, H2O and CH4 (methane).
Since CO2 is a major greenhouse gas, the radiation from the Sun is trapped in the atmosphere of Venus producing an extremely high surface temperature.
The surface temperature of Earth is around 15 degrees C (60 F). It is kept warm by the greenhouse effect. Water vapor is the most important greenhouse gas on Earth and Carbon dioxide (CO2) is second. Methane (CH4) Nitrous Oxide (N2O) Ozone (O3) and the CFCs are also relevant greenhouse gases.
The dry atmosphere of Earth is composed of :78% Nitrogen N221 % Oxygen O20.9 % Argon (Ar)Less than 0.1 % are the trace gases including CO2.
The amount of water vapor in the atmosphere varies from between 0 and 4 %.
Mean Surface Temperature =-55 C. Unlike the Earth or Venus, the atmosphere of Mars is very thin, about 1% the mass of Earth's atmosphere.
Similar Venus Its composition is 95% CO2, 3% N2, 2% Ar and less than 1% O2.
James Lovelock (Gaia) suggested that the low abundance of CO2 in Earth’s Atmosphere and the relatively high abundance of O2 is suggestive of life.
Short wavelengths correspond to high photon energy
Hot objects radiate more short wave length photons than cooler objects.
UV photons have energies above Visible light IR photon energies are lower than visible light photons
The flux of radiation is also referred to as the radiation intensity.
It is the amount of radiant energy passing through a surface area each second per unit area.
22sec m
Watts
mond
Joules
Areatime
EnergyIntensity
The Solar constant is 1365 W/m2
This is the average solar energy that reaches the Earth’s upper Atmosphere if the sun is shining directly on a solar collector.
If the collector is tilted a bit then the intensity is weaker since it is spread over a larger area.
Assume So=1000 W/m2
What is S if r=2ro?
Assume So=1000 W/m2
What is S if r=2ro?
2
2
2
2
0
02
2502
11000
21000
m
W
m
W
r
r
m
WS
Assume So=1000 W/m2
What is S if r=.5ro?
Assume So=1000 W/m2
What is S if r=.5ro?
2
2
2
2
0
02
40001
21000
5.01000
m
W
m
W
r
r
m
WS
TK=TC+273
TC=TK-273
TK=TC
The mean temperature of Earth is 15 C. What is this on the absolute temperature scale? ( Kelvin scale)
Radiation Laws
As temperature increases wavelength of maximum radiant intensity, max, increases.Wein’s Displacemnet Law.
max 3000(m K)
TK
max 3000(m K)
6000K0.5mSun
Earth max 3000(m K)
300K10.0m
Intensity T4
Black Body =1.0
Stefan_Boltzman Radiation Law.
As temperature increases total radiation output increases.
Brightness = Intensity Energy leaving an object each sec per square meter
Intensity T4
As T double Brightness increases by ___??____
As T triples Brightness increases by _______
Radiation Laws
As temperature increases total radiation output increases. Stefan_Boltzman Radiation Law.
Brightness = Intensity Energy leaving an object each sec per square meter
Intensity T4
As T double Brightness increases by 16
As T triples Brightness increases by _81 times = 3x3x3x3__
http://www.atmosedu.com/meteor/Animations/42_Selective_Absorption/42.html
30 % of sunlight incident on Earth is reflected back into space. I.e. Earth’s Albedo is 0.30 (30 %).
From K. Trenberth, J. Fasullo, and J. Kiehl, EARTH’S GLOBAL ENERGY BUDGET BAMS 2009