Activity 1.50  How the Sun's  Position Varies Each Season

Follow the Sun's circle of light during the year.

1. The following links have good explanations for what causes the seasons. 

• A good place to start:  A slide show about the seasons from the University of Akron. 
• MSN News has good information about what causes Earth's seasons. 
• The South Carolina Department of Natural Resources has some very good information about sunlight intensity.

2.  This graphic shows how the sun's rays hit the earth at different times of the year. 

At any moment, there is one location on the spherical Earth that directly faces the sun and receives vertical rays of sunlight. The location that directly faces the sun is called the subsolar point.  At the subsolar point, solar radiation is most intense: an area lying flat on the surface of the Earth intercepts the most sunlight. Also, vertical structures - buildings, posts, flagpoles - will not  cast a shadow at the time when the sun is directly overhead.  Angle-of-incidence Here's a simple demonstration you can try.  1.  Get a flashlight, a piece of graph paper, a pen and a ruler.  2.  First, turn on the flashlight and put the graph paper 2 feet below it on the floor.  Hold the flashlight directly above the paper. 3.  You will see a focused beam of light on the graph paper. Draw the outline of the beam of light.   Count the number of squares (area).  4.  Now, tilt the flashlight at a slight angle (23.5 degrees if you know how much that is!).  5.  You should now see that the same beam of light is spread over a greater area of  the paper. Draw the outline of the beam hitting the tilted graph paper.  Count the number of squares in the area you drew. 6.  Compare the areas of the two light circles.  7. Summarize in your own words what happens when the angle of the light (angle-of-incidence) increases.

3.  Review these names for special locations on the Earth:

When the Earth is oriented so its North Pole tilts directly towards the sun, the subsolar point is as far north as it can go (at its northernmost latitude), and a circle  drawn around the Earth at this latitude is called the Tropic of Cancer.  When the North Pole of the Earth is tilting directly away from the Sun, the subsolar point is  as far south as it can go. A circle drawn around the Earth at this latitude is called the Tropic of Capricorn.

4.  Where is the SSP at different times of the year?

This diagram shows the position of the subsolar point at different times of the year.  Where is the SSP at these times... Winter Solstice? Spring Equinox? Summer Solstice? Fall equinox ?

5.   Here is another way to look at it:  Try this explanation from the University of Wisconsin.

6.  Explore the relationship between light intensity and angle of incidence a little more.  Try this is a cool animation.

7.  How much do you understand about the seasons?  Try this quiz.  (Note: the quiz has some questions about information you have not learned in this lesson.  Go ahead and test your knowledge! ). 

  Compare Earth's seasons with seasons on Mars.
 
 

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