PROCEDURE

Part I: Energy of the sun

1. The average temperature of the sun is 5780 K. Using the Stefan-Boltzmann law, calculate the average irradiance of the sun.

2. The sun's radius is 7x10⁸ meters. How much total power is emitted from the sun?

3. Using the Wien displacement law, calculate the wavelength of peak emission of sunlight. What type of radiation does the sun emit primarily (e.g., ultraviolet, visible, infrared, etc.)? Use the diagram of the electromagnetic (EM) spectrum to remember the wavelength ranges of the EM bands.

4. If the ground temperature of the earth were 0 deg C, what would be the earth's irradiance and at what wavelength would this radiation be emitted? (Remember to convert temperature to Kelvin.) What type of radiation is this? 

Part II: Energy received at the earth

1. The radiative energy from the sun striking a surface perpendicular to the sun's rays at the mean earth-sun distance is called the solar constant. The solar constant is denoted mathematically as S_o. The inverse square law is used to calculate this constant:

S_o = E(sun) x (R(sun)/r)²

where

E(sun) = irradiance of the sun

R(sun) = radius of the sun = 7x10⁵ km

r = mean distance between the earth and the sun = 1.5x10⁸ km

Calculate S_o.

2. Calculate the radiative energy at the top of the earth's atmosphere on a flat plane oriented at the following angles relative to the incoming solar rays:

0 deg, 30 deg, 45 deg, 60 deg, and 90 deg



3. What can you say about the amount of radiation striking the top of the earth's atmosphere over different latitudes during an equinox?

4. If the radiative temperature of the sun were increased by 1%, what would be the new solar constant for the earth (assuming no other changes)? What percentage increase or decrease from your value of S_o (from Part II, Question 1) would this be?