The edge of the shadow between night and day on the moon is called the terminator.   How is the terminator on the Moon different from Earth's?  Look closely. .... hint - on the Moon the light will  change from day to night in just a few minutes.  On Earth you know that evening lasts for an hour or so.    What causes the difference?  Scroll down for the answer.
 
 

The 'terminator' on the Earth Source:  Earth Viewer

The terminator on the Moon Source:  Moon Viewer

What causes the difference in the edge of the terminator?  On Earth the terminator is a blurry  line - if you were down there you would see daylight change   slowly to night.   On the Moon it's a different story.  The terminator is a clear, sharp line.  The line is so clear that if you are on the Moon Day time would change to night time in only a few minutes.  It would be as if the shadow of a large cloud passed over you.

The reason?  The Earth is surrounded by a 30+ mile high blanket of air.  The air scatters the light, causing the edge of the terminator to be blurry.  There is no air or atmosphere on the Moon, so light goes all the way to the surface with nothing to stop it or to scatter it.   It causes a clear sharp shadow to be formed on the Moon.

So if the atmosphere can scatter the light,  what other ways does the atmosphere affect the Sun's light as it travels through and down to the Earth's surface?
 
 

Source: AllPosters A scene in Banff National Park, Canada.  Why is the sky blue? Which parts of the picture are most similar to the Moon picture on the right?

Source: Earth Facts An Apollo 15 astronaut looks down on the Hadley Rile,  a deep valley nearly 1.5 km (.9 mi) across at its widest point.    Notice on the Moon the sky is black!  Why?

Source: Earth Facts

An Important Thin Layer A view of Earth, showing the thin layer of atmosphere visible on the 'edge' of the  planet.  The 'edge' of any planet is called the limb of the planet. Earth's atmosphere may not seem very important in a remote picture like this, but it responsible for all life on Earth.  The Earth's atmosphere has many roles, including providing the gases living organisms need for respiration, moving heat energy around on the planet, and absorbing ultraviolet radiation from the Sun. Click here and here for more pictures of Earth's limb.

 

A Thin but Important Layer The Sun sends Energy (heat, light, and other kinds of radiation)  to the Earth.  At the top of Earth's atmosphere scientist's have measured the Energy.  They have measured 2.0 Calories/min/cm2 .  What do you think happens to the energy  as it travels down through the atmosphere to the surface of the Earth?