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The
Sun-Earth-Moon System
Planet Earth
Objectives
 Describe earth's shape and list physical data about
Earth
Compare and contrast the rotation and revolution of
Earth
Relate
Earth's tilt and revolution to the change of seasons
Earth's Shape
 A sphere is what the earth is almost
shaped like
It's
rotating at around 1,000 miles per hour (at the equator), so naturally it bulges a
little there.
Evidence
Before telescopes and space travel, how
did people know the earth was a sphere? This was, in fact, well known, by Columbus' time.
for example,
Aristotle, 384 - 322 B.C., noted that the
shadow cast by the earth on the moon during a lunar eclipse was always rounded, never
square or a line, so he reasoned that the earth must be spherical.
The moon during Lunar Eclipse:
Rotation
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Earth
rotates on its axis,
like a wheel rotates on its axle.
About
one rotation in 24 hours.
Sun, stars
appear to move because of this rotation, but it's Earth that is
moving relative to the heavens.
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Magnetic Field
[A Beginner's Guide to
the Earth's Magnetosphere]
[The
Magnetosphere]
Same
force (electromagnetic
field) as that produced by a magnet.
Earth
has North and South
magnetic poles, like a magnet!
Because: Earth has an iron core.
Note: The magnetic poles are not in
exactly the same place
as the geographic N and S poles.
Other planets have magnetic fields:
- Jupiter's is
very large,
and
very
strong:
View the
Magnetic Field of Jupiter at Views of the Solar System
(This is a large .avi movie. This
link will open it in a new browser window)
- The Voyagers' and Galileo's instruments
had to be specially protected against damage from it!
- Saturn's is much weaker than Jupiter's.
SEASONS
Factors determining the changes in earth's seasons:
Revolution:
Around the sun, (our Year) coupled with the:
TILT Of the earth's
Axis of Rotation,
and it is NOT related to the fact that:
- In fact, the Earth is farther from the sun during
the Northern Hemisphere summer than during the Northern Hemisphere winter.
ANGLE OF
INCIDENCE:
The angle at which the sun's rays strike the earth's surface.
The higher the angle, the stronger the sunshine per unit area. Also, the sun is up longer in summer than in winter.
EQUINOX
When the sun is directly above the equator [SEE IT]
Length of day = Length of night
Start of spring/fall
~20 March, ~21 September
SOLSTICE
When the sun is farthest north or south of the equator.
- Day is either longest or shortest of year.
- Start of winter/summer
- ~21 June, ~21 December
Go to:
LUNA: Earth's Moon
to continue with this lesson.
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