Name:                                                                                                  Date:                                                  EN       


The Earth receives almost all of its energy from the sun.


Compared with a billion other stars in space, the sun is reasonably typical in size, color and temperature.  Stars produce their own energy by the process of nuclear fusion.  Deep inside stars, four hydrogen atoms combine to become a single atom of helium.  A small loss in mass produces vast amounts of energy, which rise to the surface of the star by convection.  The energy is radiated as star light, most of which is lost into deep space.  But a tiny fraction of this energy reache the planets.


The solar radiation that reaches the Earth is known as insolation.  Insolation is a contraction of three words:  INcoming SOLar radiation.  Although sunlight contains a wide spectrum of wavelengths from heat rays to X-rays, solar radiation is mostly in the form of visible light.


1.     What is insolation?                                                                                                                


2.     Most of the energy that we receive as sunlight is in the                                     part of the spectrum.

3.     The sun creates energy in a nuclear reaction that converts                               into energy.



When insolation reaches Earth’s surface, the energy is reflected, scattered, refracted, or absorbed.








Dry Sand












Absorbtion of Insolation

 Smooth surfaces and light colored surfaces allow light to bounce off.  This light is reflected.  If the reflection bounces off rough surfaces, it is called scatter.  As light rays penetrate Earth’s atmosphere, they slow down as they pass into the denser air of the lower atmosphere.  This change in speed causes the light to be bent, or refracted.  Some of the light that reaches the Earth is absorbed as it changes into heat, which warms the surface absorbing the insolation.  Darker surfaces reflected less light as they absorb more light.  The table to

the right shows the ability of different surfaces to absorb sunlight.


4.     According to the table above, what kind of ground cover absorbs the most insolation?



Have you ever noticed that if you look straight down into clean, still water, you can see into the water, but if you look at a low angle, the smooth water acts like a mirror?  That’s why the albedo (reflectivity) of some surfaces is variable, depending on the angle of the sum.  In general, more sunlight is reflected if the surface is light in color, smooth, and, if the sun is low in the sky.

5.     Give two reasons that most of the sunlight received in the polar regions is reflected back into space.


1.                                                                        2.                                                             


6.     What name is applied to light that is bent in the atmosphere?      



…that bounces off smooth surfaces, like a still lake?                  



…that is taken in by the Earth resulting in the ground becoming warmer?




insolation2_0001.tiffSome insolation is randomly reflected off small particles within the atmosphere.  These particles are called aerosols.  Aerosols can be cloud droplets or ice crystals, dust, smoke, salt spray or pollution from our homes and industries.  These particles remain suspended because they are too small to fall through the air.  If you make a mixture of mud and water, some of the mud particles are small enough to remain suspended indefinitely.  Yet, they may be large enough to be visible with a microscope.  They form a suspension.  Thus, aerosol particles form a suspension within the atmosphere.


7.     What is an aerosol?                                                                                                              


8.     What affect do aerosol particles have on insolation?                                                                





9.     What portion of our insolation is reflected by aerosols, clouds, land and oceans?                        


10. What is the primary change caused by the absorption of insolation?