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The Tilting of the Earth and Various Climatic Seasons (page 2)

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Author: Janice VanCleave

Purpose

To determine how much sunlight the northern and southern temperate zones have during different seasons.

Materials

  • drawing compass
  • 8-by-8-inch (20-by-20-cm) square piece of poster board or any stiff paper
  • scissors
  • pencil
  • ruler
  • 3-by-7-inch (7.5-by-17.5-cm) piece of black construction paper
  • 9-by-12-inch (22.5-by-30-cm) sheet of yellow construction paper
  • transparent tape
  • paper brad

Procedure

  1. Use the compass to draw a circle 6 inches (15 cm) in diameter on the poster board. Cut out the circle.
  2. Use the pencil and ruler to draw two perpendicular lines across the cutout circle. Label one of the lines Equator. The other line represents Earth's axis.
  3. Draw two lines parallel to the equator line, one line ¾ inch (1.9 cm) above and the other line 21⁄4 inches (5.6 cm) above the equator. Use the pencil to shade the area between the two lines.
  4. Label the line near the equator Tropic of Cancer and the other Arctic Circle, as shown. Label the shaded area Northern Temperate Zone.
  5. Repeat step 3, drawing the lines below the equator line. Label the line near the equator Tropic of Capricorn and the other Antarctic Circle. Label the shaded area Southern Temperate Zone.
  6. Lay the black paper on the left side of the yellow sheet of paper, as shown. Secure the short edges of the black paper with tape.
  7. Slip half of the paper circle under the free edge of the black paper so that the equator line is perpendicular with the edge of the black paper.
  8. Use a pencil to make a hole through the center of the paper circle and yellow paper. Insert the paper brad through the hole.
  9. On the yellow paper and in line with the equator, draw a large arrow. Label the arrow Direct Rays.
  10. Notice how much of the northern and southern temperate zones are covered by the black paper and how much of each zone is not covered.
  11. Turn the paper circle so that the arrow points to the Tropic of Cancer. Repeat step 10.
  12. Turn the paper circle so that the arrow points to the Tropic of Capricorn. Repeat step 10.

Seasons

Results

When the arrow points to the equator, half of each temperate zone is covered and half is not covered. When the arrow is pointing toward the Tropic of Cancer, more of the northern temperate zone is uncovered than is the southern temperate zone. When the arrow is pointing toward the Tropic of Capricorn, more of the southern temperate zone is uncovered than is the northern temperate zone.

Why?

The amount of sunlight in the temperate zones, indicated in this experiment by the uncovered area of the circle, depends on the tilt of Earth in relation to the Sun. During any season, any place on the equator has the same amount of daylight, which is 12 hours. During the spring and autumn equinoxes, direct sun rays hit the equator, and all places on Earth have equal hours of daylight and night. When the Tropic of Cancer has direct sun rays, the northern temperate zone begins summer and has more daylight hours than the southern temperate zone, which begins winter. When the Tropic of Capricorn has direct sun rays, the northern temperate zone begins winter and has fewer daylight hours than the southern temperate zone, which begins summer.

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