Seasons Class Discussion Slides


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Seasons Class Discussion Slides

  1. 1. Why do we have seasons? October 17/18, 2011
  2. 2. Our Seasons <ul><li>In the United States our 4 seasons begin on the 22 nd day of the following months: </li></ul><ul><ul><li>Spring - March </li></ul></ul><ul><ul><li>Summer - June </li></ul></ul><ul><ul><li>Autumn - September </li></ul></ul><ul><ul><li>Winter - December </li></ul></ul>
  3. 3. The Reason for the Seasons <ul><li>Tilt - The Earth is tilted 23.5 degrees as it revolves around the sun </li></ul><ul><ul><li>The North Pole always points in the same direction </li></ul></ul><ul><li>Revolution - The Earth revolves around the Sun – </li></ul><ul><ul><li>The Earth completes one revolution every 365 ¼ days; 1 revolution in 1 yr </li></ul></ul><ul><li>Falls Church is in the mid-latitude region of the northern hemisphere; We have hot summers and cold winters because of the tilt of the Earth's axis </li></ul>
  4. 4. Needed background information <ul><li>Allentown, Pennsylvania is only 202 miles northeast of Falls Church, Virginia – They have similar latitude and insolation characteristics. </li></ul>
  5. 5. The Reason for the Seasons <ul><li>Because Earth’s axis is tilted it leans: </li></ul><ul><ul><li>Towards the Sun (Summer) </li></ul></ul><ul><ul><li>or 6 months later </li></ul></ul><ul><ul><li>Away from the Sun (Winter) </li></ul></ul><ul><ul><li>In between these postions, Spring and Autumn occur </li></ul></ul>
  6. 6. FALSE! <ul><li>Changes in the distance between Earth and the sun cause the seasons </li></ul><ul><ul><li>In fact, the Earth is farthest from the sun (aphelion) in July, and is closest to the sun (perihelion) in January! </li></ul></ul>
  7. 7. FALSE! <ul><li>The seasons are caused by the Earth’s axis flipping back and forth. </li></ul><ul><li>Can’t be true because we observe: </li></ul><ul><ul><li>Circumpolar stars </li></ul></ul><ul><ul><li>Earth’s north axis always </li></ul></ul><ul><ul><li>pointing towards Polaris, </li></ul></ul><ul><ul><li>a change in seasons </li></ul></ul>
  8. 8. TRUE! <ul><li>The Earth's movement around the sun causes the seasons </li></ul><ul><ul><li>In the summer the axis points slightly toward the sun </li></ul></ul><ul><ul><li>In the winter, the axis points slightly away from the sun </li></ul></ul><ul><li> </li></ul>
  9. 9. Summer Time <ul><li>The sun is higher in the sky and the energy that we receive from the sun is more direct </li></ul><ul><li>The sun remains in the sky for a longer period of time </li></ul><ul><li>Higher sun & longer days mean – </li></ul><ul><ul><li>direct energy </li></ul></ul><ul><ul><li>greater amounts of energy being absorbed by the Earth’s surface </li></ul></ul><ul><ul><li>Temperatures must go up </li></ul></ul>
  10. 10. Winter Time <ul><li>The sun is lower in the sky and its energy distribution is more spread out </li></ul><ul><li>The sun is visible for a much shorter time during the day </li></ul><ul><li>Lower & fewer hours of sun means – </li></ul><ul><ul><li>indirect energy </li></ul></ul><ul><ul><li>less energy received/absorbed </li></ul></ul><ul><ul><li>Temperatures must go down </li></ul></ul>
  11. 11. The Sun’s Changing Position <ul><li>The sun is in the sky higher (in elevation) for longer in the summer, SO </li></ul><ul><ul><li>It takes longer to rise and set from horizon to horizon and has more time to heat up Earth </li></ul></ul>
  12. 12. What happens when the sun changes positions ? <ul><li>The sun changes from providing direct to indirect sunlight </li></ul><ul><li>Direct during summer • Indirect during winter </li></ul>
  13. 13. What happens to shadows when the sun changes positions ? <ul><li>Summer: shorter shadows </li></ul><ul><ul><li>Sun is higher in the sky </li></ul></ul><ul><li>Winter: longer shadows </li></ul><ul><ul><li>Sun is lower in the sky </li></ul></ul>
  14. 14.                                                                                                         ENERGY AND THE EARTH’S SHAPE : Because the Earth is in the shape of a sphere, there will be parts of the Earth that receive direct energy from the sun and other regions of the world that receive indirect energy. Notice the Earth’s axis in this drawing. The axis is the imaginary line about which the Earth spins. It is straight up and down. If this is how the Earth went around the sun each year, the seasons would always remain the same.
  15. 15. The Solstices <ul><li>&quot; Solstice &quot; </li></ul><ul><ul><li>&quot; sol &quot; from the Latin meaning sun </li></ul></ul><ul><ul><li>&quot; sistere, &quot; from the Latin meaning cause to stand still </li></ul></ul><ul><li>The longest (summer) or shortest (winter) day of the year </li></ul>Summer solstice Winter solstice
  16. 16. Summer Solstice (Northern Hemisphere) <ul><li>The summer solstice is the first day of summer (about the 21st June) </li></ul><ul><li>The longest day of the year in the Northern Hemisphere </li></ul><ul><li>When the North Pole is leaning more directly toward the sun than it does on any other day </li></ul><ul><li>It is the point when the sun shines directly over head of the tropic of Cancer, the northernmost reach. </li></ul>
  17. 17. Winter Solstice <ul><li>The winter solstice (20th/21st December) is the first day of winter </li></ul><ul><li>The shortest day of the year </li></ul><ul><li>The winter solstice in the Northern Hemisphere occurs when the North Pole is leaning away from the sun </li></ul><ul><li>It is the point when the sun shines directly over head of the Tropic of Capricorn, the southernmost reach. </li></ul>
  18. 18. The Equinox <ul><li>When the North Pole is pointing neither directly toward nor directly away from the sun </li></ul><ul><li>Equal periods of light and darkness </li></ul><ul><li>The halfway mark between summer and winter solstices </li></ul><ul><ul><li>March 20 /21 </li></ul></ul><ul><ul><ul><li>First day of Spring; North pole begins to turn back towards from the sun </li></ul></ul></ul><ul><ul><li>September 20 /21 </li></ul></ul><ul><ul><ul><li>First day of Fall; North pole begins to turn away from the sun </li></ul></ul></ul>
  19. 19. Reviewing what you learned: <ul><li>Read pages 80-83 in your textbook. </li></ul><ul><li>In your notebook, answer the section review questions for section 4.3 #1-3 on page 83, and question #18 on page 87. </li></ul>