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Earth Motions
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Earth Motions
1. Rotation- spinning
of the Earth about
its axis
• Cause of day and
night.
• Solar day is 24
hours, from noon
to noon.
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Sidereal Day
• Earth makes ONE complete rotation (360o)
in 23 hours and 56 minutes.
• Click HERE for an animation.
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2. Revolution- Earth’s orbit about the sun.
– Elliptical orbit (not a perfect circle)
– Perihelion- the earth is closest to the sun
 Jan 3rd (147 million km)
Earth moves the fastest in orbit
– Aphelion- farthest from the sun
 July 4th (152 million)
Earth moves the slowest in orbit
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Milankovitch Cycles
• Long-term earth movement. Can be from
10s of thousands of years to 100s of
thousands of years.
• Linked with
global climate
change.
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Earth motions- Milankovitch Cycles
3. Precession- wobbling of the Earth like a top.
• one complete wobble  26,000 years (cause
of the changing North Star)
• Precession does NOT change the angle Earth
is tilted, just the
direction it is
pointed.
• Does not change
climate, but does
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change WHEN we experience seasons.
Inclination of the Axis
• Obliquity- Earth’s axis
changes its tilt from more
straight up and down to more
tilted.
• the Earth’s axis is currently
tilted 23.5o from the ecliptic.
• changes 22.2 to 24.5 through
a 41,000 year period.
• Tilt of the Earth is the cause of
the Seasons. If you change
the tilt then you change the
seasons.
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Eccentricity
•
•
•
Eccentricity- HOW elliptical the orbit of
the planet is around the sun.
100,000 year period from high to low
eccentricity.
Click HERE for a website review of
Milankovitch cycles
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