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Earth
Physical Characteristics of Earth
1. Spherical shape
-satellite photos
-curved shadow on
moon during a lunar
eclipse.
-approaching ships
“rise” over the
horizon
Physical Characteristics of Earth
2. Rotation
-Earth spins on its
axis (an imaginary
vertical line) causing
night and day.
-24 hours to rotate
once on its axis
-rotates 365 times in
a year
https://www.youtube.com/watch?v=R3jr0DaV8N8
Foucault’s Pendulum shows the
Earth’s rotation as it swings
Physical Characteristics of Earth
3. Magnetic Field
-Movement of
liquid iron inside
Earth and its
rotation create a
magnetic field.
-Helps protect
Earth from harmful
CME’s from the
sun.
Physical Characteristics of Earth
4. Revolution
-Earth’s yearly orbit around the sun. (365 ¼
days)
-Path is elliptical in shape.
Farthest
away
from sun
in July
Closest
to sun in
January
What causes the seasons?
?
?
?
What do you know about the
Seasons?
• Summer
– NJ-warm, longer days,
June-August
– Hawaii-80’s, 12 hours
of light
– Alaska- up to 24 hours
of light
– Australia-Dec-Feb
• Winter
– NJ-cold, longer nights,
Dec-Feb
– Hawaii- 70’s, 12 hrs of
light
– Alaska-up to 24 hours
of darkness
– Australia-June-Sept.
Distance from the sun does NOT
cause our seasons.
• If it did, we would all feel winter in July and
summer in January. Even Hawaii would
have a cold winter!
Physical Characteristics of Earth
5. A Tilted Axis
23.5˚ tilt
-The Earth is
always tilted the
same direction
during its yearly
revolution
around the sun.
• Sunlight strikes the hemisphere tilted
towards the sun more directly than the
hemisphere tilted away.
• Summer occurs in the hemisphere tilted
towards the sun. (direct light)
Sun
Direct Light
• Areas receiving direct light from the Sun
have a greater amount of sunlight,
therefore higher temperatures.
Northern Hemisphere-Winter
What
season
is
it?
Southern Hemisphere-Summer
Sun
So what causes the seasons?
• The Earth’s tilt causes the seasons!
http://lhsgems.org/Presentations/SSS%203-8%20NSTA%202009%20final.ppt#362,35,Another Model for Distance
Solstice
• The day when the sun reaches its greatest
distance north or south of the equator.
• Northern Hemisphere- (opposite of S. Hemi)
– Summer solstice: June 21 or 22 (longest
period of daylight of the year)
– Winter solstice: December 21 or 22 (shortest
period of daylight of the year)
The sun’s path across the sky is
higher in the summer and lower in
the winter
http://www.newscientist.com/blogs/shortsharpscience/2011/10/about-time-beer-can-freezes-ti-1.html
Equinox
• When the sun is directly above the Earth’s
equator. Daylight hours are nearly equal
all over Earth.
– Neither the N. or S. Hemisphere is tilted
towards the sun.
– Spring equinox-March 20 or 21
– Fall equinox-September 22 or 23
Seasons demos
• https://www.youtube.com/watch?v=DD_8J
m5pTLk
• http://esminfo.prenhall.com/science/geoani
mations/animations/01_EarthSun_E2.html
http://spiff.rit.edu/classes/phys301/lectures/gas_planets/Seasons_Nav.swf
Northern Hemisphere Solstice and Equinox
positions
Seasons are opposite for the Southern
Hemisphere
Review Quiz
Which diagram correctly shows Earth’s orbit around
the sun?
Identify for the N. Hemisphere:
1. Summer solstice
2. Winter solstice
D
3. Fall equinox
Spring
4. Spring equinox
C
A
Winter
Summer
B
Fall
How do we know the Earth is a
sphere?
-satellite photos
-curved shadow on moon during a lunar
eclipse.
-approaching ships “rise” over the horizon
What is an axis?
• The imaginary vertical line around which
the Earth spins.
What does “A” represent? What
does “B” represent?
A-Revolution
B-Rotation
B
A
How long does one complete
rotation take on Earth?
• 24 hours
How long does one complete
revolution of Earth take?
• 365 days (1 year)
Why is a magnetic field important?
• It protects Earth from CME’s from the Sun
How do we have a magnetic field?
• The motion of the liquid metal inside Earth
and our daily rotation cause it.
What causes the seasons?
• TILT! TILT! TILT!
What season is it in the Southern
Hemisphere?
• Summer-southern hemisphere is tilted
towards the sun = direct light = summer!
Sun
What type of light makes hotter
temperatures?
• Direct!
Where is the sun during the
equinox?
• Directly over the equator.
What’s the difference between
northern and southern
hemispheres’ seasons?
• They are opposite!
Christmas (December)
in Australia is warm!
Easter is celebrated in the
fall (March or April)
• http://www.teachnology.com/worksheets/science/earth/4/