Earth in Space - PowerPoint by 62I0JCj

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									Earth in Space

  Section 19.1
Earth’s Shape


• Considered to be ellipsoid
     Oblate spheroid
• Earth is wider
     than it is tall
• Bulges at equator,
     flattened at poles
Earth’s motions




• Rotation – spinning on an axis
    - causes day and night
Earth’s Motions


 1. sidereal day
  The time it takes the Earth to
   rotate once with respect to a
   reference star.
 • One 360° Rotation
 • Time = 23 hr. 56 min.

                         1-2: Globe rotates 360° - sidereal
                         1-3: Globe re-points to sun - synodic
Earth’s motions



   2. solar (synodic) day = 24 hours
      The time it takes Earth to rotate
      once with respect to the sun.
      (Sun’s Highest point in sky to the
      next highest point in sky).
Earth’s Motions




• Revolution – movement around a fixed
  point (sun)
Earth’s Motions




 - Revolves once every 365.25 days (year)
     need leap years
 - elliptical shaped orbit
 - Jan. 3 - 147 million km from sun
 - July 4 - 152 million km from sun
 Seasons on Earth


                         o
• Earth’s axis is tilted 23.5
• The area tilted towards sun has longer
  days and more radiant energy (summer)
• The area tilted away from
  the sun has shorter days
  and less radiant energy (winter)
                      Vernal equinox    Solstice – the sun
                      March 20 or 21    reaches the greatest
                                        distance north or
                                        south of the equator




Summer solstice
June 21 or 22                             Winter solstice
Longest day                               Dec 21 or 22
                                          Shortest day

Equinox- the sun
is directly above
the equator.
Equal daylight
and night time
                     Autumnal equinox
hours all over the
                     Sept 22 or 23
world
Earth’s Motions
• Precession –
  Earth’s wobble
Earth’s Orbit


• Law of
  universal
  gravitation:
  every object in
  the universe
  attracts every
  other object.     Isaac Newton
• Attracts all objects towards each other.
  • Depends on two factors:


    MASS                      DISTANCE
The amount of
matter (stuff)
in an object
                                 STRONGER
    MASS           VS      WEIGHT
• The amount of         • Force ( a push
  matter (stuff)          or pull) of
  in an object            gravity on an
                          object.


• Does not              • Changes
  change                  depending on
                          where you are.
265 lbs




            =120 x 1.6
          About 45 lbs
Earth’s Orbit
• Inertia – the tendency of an object to resist
  change in motion

• Newton’s first law of motion

• An object in motion will stay in motion, in
  straight line, at a constant speed unless
  acted upon by an outside force
Earth’s Orbit
                                     Inertial force
    Newton
concluded that       Gravitational
    2 forces         force

(inertia, gravity)
combine to keep
  Earth in orbit
 around the sun

								
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