Definitions:

 

Earth-sun relations

 

Circle of Illumination -- the imaginary line that passes divides the globe into a night-half and a day-half (sometimes called the Terminator).

 

Subsolar Point -- the point at which the sun's rays strike the earth directly (at a 90o angle).

 

Radiation

 

 Solar constant--the amount of energy that arrives from the sun at the top of the atmosphere on a plane perpendicular to the sunÕs rays.  For the earth, this averages out to be around 2 cal per cm2 per min.  This is often written 2 cal/cm2/min. 

 

Emission--produced by or given off by...

 

Electromagnetic Radiation--the form of energy emitted by any object that has a temperature greater than 00K. (Often called radiation.).  Characterized by wavelength and intensity (amount).

 

Insolation--the amount of radiation that after passing through the atmosphere makes it to the surface of the earth.

 

Laws of Radiation--physical principles that govern the amount and characteristics of the electromagnetic energy emitted by an object.

 

Electromagnetic Spectrum--the collection of wavelengths of radiation possible in the universe

 

Solar Spectrum--the collection of wavelengths of radiation emitted by the sun.

 

Terrestrial or EarthÕs Spectrum--the collection of wavelengths of radiation emitted by the earth.