Download Chapter 22

Chapter 23
Sun, Earth, Moon System
• Position?
• Center of the universe?
• No, the Sun is the center of our solar system; Earth
travels around the Sun.
• Shape?
• Flat? Would you fall off if you went too far?
• No, the Earth is a sphere. Spheres are round, 3-D,
and all points on the surface a equidistant (??) from
the center.
• EVIDENCE: Aristotle:
» Earth casts curved shadow
» Appearance of approaching ships
» Pictures from space probes and satellites.
Motion
• Earth rotates around an
imaginary line called the
axis.
• This causes day and night.
• One rotation = 24 hours
• Rotates 365 times in a
year
• Earth also revolves around
the Sun
• Revolution = 1 year
Rotation causes…..
• Day and night
– Rotates
counterclockwise or
East to West
• Changes in position of
Sun, stars, planets
– Sun rises in the East
sets in the West
– Observed position
changes are due to
rotation of Earth.
Revolution
One trip around the Sun!!!
** Revolution = length of a year
(Closer planets have shorter years, farther
planets have longer years)
** Orbit = path the Earth takes around the Sun
* Ellipse = shape of the Earth’s orbit.
• http://www.mathsisfun.com/earth-orbit.html
Get your partner to say the following!!
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SPHERE
REVOLUTION
ROTATION
YEAR
ARISTOTLE
EAST TO WEST
ELLIPSE
ORBIT
Revolution
• Closest to Sun in
January????
• Farthest in July???
• Then what causes
seasons???
Tilt
• The Earth is tilted on its axis at about
23.5o
• Daylight hours are longer for the
hemisphere tilted toward the SUN!!
• This hemisphere also receives more
INTENSE RADIATION from the Sun.
http://astro.unl.edu/naap/motion1/animations
/seasons_ecliptic.html
• http://highered.mcgrawhill.com/sites/007299181x/student_view0/c
hapter2/seasons_interactive.html
Equinoxes
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Sun is directly over the equator.
Equal hours of day and night.
Neither hemisphere is pointed toward Sun
Happens twice/year
– N. Hemisphere
»Spring = March 21 or 22
(Vernal Equinox)
»Autumn = September 21 or 22
(Autumnal Equinox)
Solstice
• Point at which Sun reaches greatest
distance north or south of equator.
• Happens twice/year
»June 21 or 22 (Summer Solstice)
»MOST DAYLIGHT
»December 21 or 22 (Winter Solstice)
»MOST NIGHT
Get your partner to say the
following:
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Sphere
Axis
Rotation
Revolution
Ellipse
Equinox
Solstice
Get your partner to say the
following:
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24 hours
365 days
Autumn
Orbit
Tropic of Cancer
June 21 or 22
March 21 or 22