The Sun and the Seasons

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The Sun and the Seasons
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Objectives

• Describe how Earth moves through space
• Explain how seasons are caused by the tilt of
  Earths axis
• Explain why different latitude zones have
  different average temperatures

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Earths Movement

• Earth moves in two major ways rotation and
  revolution
• Earth spins like a top around the axis that
  connects the north and south geographic poles
• Rotation causes day and night and is from west
  to east (so sun appears to move east to west
• Revolution movement of one body in space around
  another
• Broad path or orbit takes 365 ¼ days

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Earths Latitude Zones

• Latitude distance in degrees north or south of
  the equator
• Equator is at 0 and the North Pole is at
  90north
• So, warmer near equator and colder toward the
  poles
• Scientists use lines of latitude to mark out
  three different types of regions within which
  temperatures are generally similar the tropic,
  temperate, and polar zones

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Climate Zones.Maslowski Wildlife
Productions, 2000. Video Segment.27 October
2010. lthttp//www.discoveryeducation.com/gt.
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The Seasons

• The axis tilts at an angle of about 23.5
• So the north end of Earth always points in the
  same direction (North Star)
• The orientation changes relative to the sun over
  the course of the year
• The seasons are caused by the tilt of Earths
  axis as it moves around the sun

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Solstices

• Because Earths axis is tilted, the latitude at
  which the noon sun appears directly overhead
  changes each day according to a yearly cycle
• A solstice occurs on the two days each year when
  the sun is directly overhead at latitude
  23.5north or 23.5south
• The seasons are not affected by Earths changing
  distance from the sun

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Equinoxes

• Neither hemisphere is tilted toward the sun
• The lengths of daylight and darkness are
  approximately equal
• Vernal equinox spring (March 21)
• Autumnal equinox autumn (September 22)
• The noon sun id directly overhead at the equator

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