Section 2: Solar Energy to Earth and the Seasons

SLOs: solar energy, Earth energy budget and hemispheres, seasons plus solstices and equinoxes.


Lesson 1:

Instruction

The Sun is a star like billions of others in the Milky Way Galaxy.  It emanates energy to the planets in our solar system, including Earth.  In the case of Earth, life exists because of this solar energy as well as the tilt and rotation of Earth; producing patterns of daylength and Sun angle which are ever changing with each day, season, and year.  The shape of Earth's orbit around the Sun is elliptical, like an oval.  Earth is closest to the Sun (at perihelion) during the winters on the Northern Hemisphere and farthest from the Sun (at aphelion) during the summers on the Northern Hemisphere.  The perihelion and aphelion all take place on the plane of the ecliptic, or the path Earth follows around the Sun.  Earth's atmosphere has changed over billions of years, from the contents of the original solar nebula which formed Earth into the atmosphere that sustains such diverse life forms today.          

Photos and Images
 (the Sun above Ventura County)  

Quiz

Since Ventura County is within the Northern Hemisphere, is the Earth closer to perihelion or aphelion right now?  Go outside during the day time when the sun is clearly visible.  Let the Sun shine a portion of your bare skin.  Can you feel the energy from the Sun?

 


Lesson 2:

Instruction

Energy from the Sun first reaches the top of the atmosphere at the thermopause.  It is then either scattered or absorbed throughout the atmosphere, back into space, within the atmosphere, or down to Earth's surface (termed, insolation).  However, even when insolation occurs, a portion of that energy will eventually be emitted into space again.  The electromagnetic spectrum of radiant energy is shown below.  The shorter wavelengths of energy enter Earth's atmosphere while the longer wavelengths of energy leave Earth's atmosphere all over the world.  The amount of energy entering and leaving any part of Earth is called the Earth Radiation Budget (ERB).  The subsolar point is the place on Earth receiving the maximum insolation, where the Sun is perpendicular (at a 90 degree angle) to the Earth's surface.  During the vernal equinox (March 20-21) and the autumnal equinox (September 22-23), the subsolar point is at the Equator (0 degrees latitude).  During the summer solstice (June 20-21) and the winter solstice (December 21-22), the subsolar point is at the Tropic of Cancer (in the Northern Hemisphere) and the Tropic of Capricorn (in the Southern Hemisphere), respectively.    

Photos and Images

 
(the electromagnetic spectrum) (the Earth, Equator, Tropics, and Poles)

Quiz

Use the image of the Earth above to generally determine, based on the time of year, where the subsolar point is.  Since the Ventura County is located between 32 degrees and 36 degrees North latitude, can the subsolar point ever be in Ventura County?   

 


Lesson 3:

Instruction

The seasons are determined by the position of the Sun in relation to Earth (altitude and declination) and the length of the days (daylengths).  The altitude is the angle between the Sun and the horizon, while the declination is the subsolar point latitude.  Daylengths are the duration of sunlight exposure from sunrise to sunset.  Earth's seasons also result from the revolution of Earth around the Sun (1 year), the rotation of Earth on its axis (24 hours), the tilt of Earth's axis (23.5 degrees), the axial parallelism (or consistent alignment of Earth while orbiting the Sun), and the sphericity of Earth (also known as the elliptical shape of a planet).  During the equinoxes, the Sun is directly above the Equator; allowing sunlight to be distributed evenly in both the northern and southern hemispheres (12 hour days and 12 hours nights are observed).  However, at the solstices, the Sun is either directly over the Tropic of Cancer (denoting Northern Hemisphere summers/Southern Hemisphere winters: 24 hours of light at the north pole, 0 hours of light at the south pole), or over the Tropic of Capricorn (denoting Northern Hemisphere winters/Southern Hemisphere summers: 0 hours of light at the north pole, 24 hours of light at the south pole).  All these features at different times of the year mean that we get fours seasons: fall, winter, spring, and summer.         

Photos and Images

(0 degrees latitude) (23.5 degrees north latitude) (23.5 degrees south latitude)

Quiz

Which of the images above is an example of the fall equinox, the winter solstice, the spring equinox, and the summer solstice for the Northern Hemisphere (note: one image represents two of the examples)? Right now in Ventura County, what season is it?  Are there more hours of daylight in the northern hemisphere (including Ventura County) or the southern hemisphere?  Why?   


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2006 Jessica Douglas