Earth 002

Tuesday, January 26th, 1999
Announcements:

Lecture notes:

HEAT ENGINES

• Interior --> radioactive decay
• Solar Energy --> generated by the sun

• Distance from the sun is very important--farther from the sun, the colder it'll be
• Albedo-reflectivity of the planet
   

ELECTROMAGNETIC SPECTRUM

• In the electromagnetic spectrum, light appears to travel as a wave

• Light is divided into many different wavelengths
• High Frequency --> Short Wavelengths (ex. gamma rays, x-rays)
• Low Frequency --> Long Wavelengths (ex. microwaves, radio waves)
• Visible lights wavelengths are between 400-700 nanometers (.4-.7 meters) long

• Short Wavelengths-->Higher Frequency-->More Energy
• Long Wavelengths-->Lower Frequency-->Less Energy

ENERGY

• What governs how much energy we get?
• Blackbody-a perfect emitter and/or perfect absorber
• Hot bodies emit a higher temperature
• Short wavelengths-->Higher frequency-->More Energy-->Higher Temperature

• Total energy flux of any blackbody: Ftot = 6T^4 (T=temp, 6= 5.67 * 10^-8)
• SUN Ftot = 6.0 * 10^7 w/m2 (watts per meter squared)
• EARTH Ftot = 1370 w/m2 (watts per meter squared)

INVERSE SQUARE LAW

• So (Ro/R)^2 = S (So=sun's energy flux, Ro=sun's radius, S=total energy emitted by sun)
• The farther from the sun, the less energy received
• Triple the distance from the sun --> 1/9 the original energy
• Double the distance from the sun --> 1/4 the original energy

ENERGY BALANCE OFF EARTH

• Ein = Eout
• S/4 (1-A) = ? 6(Te^4) (S=1370, A=.3, 6=5.67*10^-8, Te=-18 C)
• shorter wavelength->higher frequency->more energy->higher temperature
• HOT BODY RADIATES MORE ENERGY AT SHORTER WAVELENGTHS