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					Chapter 19, Section 1
   Earth in Space
  Wednesday, April 28, 2010
      Pages 636 -- 643
                              Objectives
Identify the effects of Earth’s rotation and
 revolution.
Explain the causes of the seasons on Earth.
               Vocabulary Words
 Astronomy       Latitude
 Axis            Solstice
 Rotation        Equinox
 Revolution      Vernal equinox
 orbit           Autumnal equinox
                                  Astronomy
Ancient Egyptians were among the first
 people to study the stars.
  They relied on the stars to predict the annual
   flood.
  They relied on the stars to plant their crops
Astronomy is the study of the moon, stars,
 and other objects in space.
                                                    Rotation
                                    Earth’s axis is an
                                     imaginary line that passes
                                     through the Earth’s
                                     center and the North and
       QuickTime™ and a
                                     South Poles.
        decompressor
are neede d to see this picture.
                                       The North end points
                                        toward Polaris
                                       The Earth spinning on its
                                        axis is called rotation.
                                       Earth’s rotation on its axis
                                        is what causes day and
                                        night.
                                                          Revolution
                                                   In addition to rotation,
                                                    the Earth also travels
                                                    around the sun.
                QuickTime™ and a
                   decompressor
          are need ed to see this picture.         The Earth’s movement
                                                    around the sun is
                                                    called a revolution.
                                                      One complete
                                                       revolution around the
                                                       sun is called an orbit.
Earth’s orbit around the sun -- notice that the
orbit is not quite a circle -- it’s oval shape!
 The Egyptians were                    Calendars
  one of the first
  civilizations to use a
  calendar.
    Egyptian astronomers
     would count the
     number of days                  QuickTime™ a nd a
                                       decompressor
     between each first       are need ed to see this picture.
     appearance of the star
     Sirius.
    They found that 365
     passed between each
     sighting
                      Calendar -- cont’d
 Earth’s orbit around
  the sun takes about
  365 1/4 days.
 We view this as 3
  years of 365 days and             QuickTime™ and a
                                     decompressor

  1 year of 366 days
                             are neede d to see this picture.




  (leap year)
                                                 Seasons
 Most places have 4
  distinct seasons.
    Winter
    Spring
    Summer
    Autumn (Fall)
                                QuickTime™ and a

 While there are 4               decompressor
                          are neede d to se e this picture.

  distinct seasons, the
  temperature will vary
  depending on where
  you live.
                        Seasons -- cont’d
 Earth has seasons
  because its axis is
  tilted as it moves
  around the sun.




                          It’s warmer near the equator because sunlight
                          hits Earth’s surface at a direct angle. The sunlight
                          is spread out more in the other areas.
                                Earth in June
 In late June, the Earth’s axis is tilted toward the
  sun.
 The hemisphere that’s tilted toward the sun has
  more hours of daylight.
 The combination of direct sunlight and longer
  hours gives us summer in the Northern
  Hemisphere.
 At the same time, there is less sunlight and fewer
  hours, giving us winter in the Southern
  Hemisphere.
                  Earth in December
People in the Southern Hemisphere
 receives the most sunlight giving them
 summer.
The Northern Hemisphere will receive
 indirect sunlight giving us winter.
                                  Solstice
There are two days each year when the
 noon sun is overhead at either 23.5 degrees
 south or 23.5 degrees north.
These days are called solstice.
23.5 degrees south is called winter solstice
 ( around 12/21 is shortest day of the year)
 and 23.5 degrees north is called summer
 solstice (around June 21 is longest day of
 the year).
                  Earth in March and
                          September
Halfway between the winter and summer
 solstices, neither hemisphere is tilted
 toward or away from the sun.
This happens on only two days each year.
The noon sun is directly overhead at the
 equator.
These days are called equinox
                 Earth in March and
                September -- cont’d
Vernal equinox is also known as spring
 equinox and it’s usually on March 21.
The vernal equinox marks the beginning of
 spring in the Northern Hemisphere.
Autumnal equinox is usually around
 September 23 and marks the beginning of
 fall in the Northern Hemisphere.
      QuickTime™ and a
        decompressor
are neede d to see this picture.
                    Review Questions
Explain the process that causes day and
 night.
What two factors cause the cycle of the
 seasons?
Compare rotation and revolution.
What is solstice? How does solstice relate
 to the position of the Earth’s axis?
What is equinox? How does equinox relate
 to the position of the Earth’s axis?
                               Homework
Workbook 19.1 (4/30)
Vocabulary quiz 19.1 (4/30)

				
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