http://www.youtube.com/watch?v=taHTA7S_JGk&safe=active
Unit 1 Earth’s Dimensions
• The Earth has an Oblate Spheroid
Shape
• Polar Circumference= 40,008 km
• Equatorial Circ. = 40,076 km
• Polar Diameter = 12, 714 km
• Equatorial Diameter= 12, 757km
• The Geographic poles are at the
ends of the Earth’s Axis of
Rotation. The axis is tilted at an
angle of 23 ½ degrees
• Although the Earth is not a perfect
sphere it is very close as compared
to the size of its diameter.
• The Earth has very little relief
compared to its diameter.
• If you compare the highest
mountain to the deepest ocean we
find that the Earth is smooth.
EXAMPLE
•
Mount Everest is 9km high
• The Marinas Trench is 11km deep
• 20 km as compared to 12, 757km
less than 0.2% of the diameter
• On a normal 20cm globe Mt
Everest would be 1/10th of a
millimeter.
Evidence of the Earth’s Shape
• 1. Altitude to Polaris(North
Star)- is located directly over the
Earth’s Axis of Rotation.
Therefore the angle above the
horizon to Polaris in the northern
hemisphere is equal to the
observer’s latitude
•The altitude to Polaris at any place
in the Northern Hemisphere is equal
to it’s latitude.
•The latitude at any given point on
the Earth is equal to the angle from
the equator to a radius line that
extends to the point on the surface
• 2. Lunar Eclipses- The shadow
of the Earth cast on the moon’s
surface is round.
• During a lunar eclipse the
Earth’s curved shadow is
cast on the moon.
• 3. Gravity Measurementgravity is the force that pulls all
objects toward the center of the
Earth.
• Weight = mass x gravity
• Describe how this can be used
to determine the shape of the
Earth
• As you move away from the
Earth gravity decreases.
• The distance from the center of
the Earth to the poles is less
than the distance to the equator,
• Therefore gravity is greater at
the poles.
• 4. As an observer on shore watches a
ship sail out to sea the ship will appear
to sink into the sea as it passes over
the horizon. This occurs due to the
ship following the curvature of the
Earth.
Observer
Observer’s Line of Sight
Ship
5. Photographs from space are
the best evidence of the Earth’s
shape.
Proofs of the Earth’s Shape
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Pictures of the Earth from Space
Other Objects in the Sky
Lunar Eclipse
Ships Sailing Out to Sea
The Changing Altitude of Polaris
The Change in Gravity on Earth
Distance Between Adjacent Lines of
Latitude
Earth’ Motions
Earth rotates on its axis at a rate of
15⁰ per hour.
Earth’s rotation causes the
apparent motion of the sun
They appear to revolve around the
Earth, but it doesn’t the Earth is
moving around the sun
All the stars seem to rotate around
Polaris throughout the night.
The pattern of stars also change
throughout the year. They also
move around Polaris.
Circumpolar Star Trails
Proofs of the Earth’s Rotation
• Motion of a Foucault
Pendulum
–Jean Foucault - 1851
• Coriolis Effect
–Deflection in the Northern
Hemisphere
–Deflection in the Southern
Hemisphere
Foucault
Pendulum at
the United
Nations
Winter
Orion
Earth
Sun
Summer
Sagittarius
Orion
Winter
Constellation
in the
Southern Sky
Sagittarius - Summer Constellation in the
Southern Sky