Aim: What is the reason for the seasons?

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• Aim What is the reason for the seasons?

Seasons animation
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Seasons diagram in Northern Hemisphere
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A Two Reasons

• 1. The tilt of the Earths axis
• a. When a hemisphere is tilted toward the Sun,
  the season is summer
• b. When a hemisphere is tilted away from the Sun,
  the season is winter.
• 2. The revolution of the Earth around the Sun
• The hemisphere that points toward the Sun changes
  as the Earth revolves around the Sun causes
  seasons to change.

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B. Earths tilt creates uneven heating

• The earth is tilted 23.5 o in relation to the
  sun.
• The tilt causes the sun to hit the earth at
  different angles.causing different
  temperatures.
• This is called the angle of insolation. Higher
  anglesstronger sunlight

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ESRT periods of revolution
Planets Period of Revolution Around the Sun
Mercury 87.96 Earth days
Venus 224.68 Earth days
Earth 365.25 days
Mars 686.98 Earth days
Jupiter 11.862 Earth years
Saturn 29.456 Earth years
Uranus 84.07 Earth years
Neptune 164.81 Earth years
Pluto (dwarf planet) 247.7 years
Which planet is goingFastest? Slowest?
The farther the planetthe faster the orbital
speed!
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Questions

• If the Earths orbit is a 360o ellipse, and it
  takes 365.25 Earth days to revolve.Approximatel
  y how many degrees per day does the Earth travel
  in its revolution?A) 1 B) 3 C) 10 D) 30

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C. Definitions

• 1. Revolution The movement of a planet in its
  orbit around the Sun.
• 2. Orbit The path a planet takes around the
  Sun.
• 3. Path is slightly oval shaped called an
  ellipse. An oval shaped orbit is referred to as
  elliptical. The farther away the planet, the
  longer the period of revolution.
• 4. Season The change in temperature caused by
  the earths tilt as it revolves around the sun.

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D. Seasons have nothing to do with distancethe
N.H. is in summer when Earth is farther away from
the sun.
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E. Animations of the The Earths Orbit
Earths Orbit
seasons animation
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Label Seasons diagram.
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The Tropics
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F. What is a solstice? When the Suns direct rays
(strongest) reach farthest north or farthest
south of the equator.

1. Summer Solstice in N.H. June 21
2. First Day of Summer, longest daylight hours
3. Strongest (direct) rays hit north of equatorat
   the tropic of cancer (noon sun directly overhead)

Sunrise N of ESunset N of W
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• Winter Solstice in N.H. December 22
• First Day of Winter, shortest daylight hours.
• Strongest (direct) rays hit south of the equator
  at the tropic of capricorn (noon sun directly
  overhead)

Sunrise S of ESunset S of W
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G. What is an Equinox?

• 1. The direct rays of the Sun are striking at
  the equator (noon sun directly overhead)
• 2. All places on Earth have equal hours of
  daylight and night
• Autumnal Equinox
• First Day of Fall in N.H., September 21
• Vernal Equinox
• First Day of Spring in N.H., March 21

Sunrise due ESunset due W
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Varying daylight hours.
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Summer in the Arctic

• http//www.youtube.com/watch?vJ9eCK7rWMNE

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Seasons animation
http//kids.msfc.nasa.gov/earth/seasons/EarthSeaso
ns
sun at solstice in north pole
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Summary effects of Earths tilt

• Seasons (Angle if insolation)
• Higher angle warmer season
• Lower angle cooler season
• Little change at the equator no seasons
• Different amounts of daylight hours (duration of
  insolation)
• Longer duration warmer days
• Shorter duration cooler days

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Insolation Chart
Intensity of Insolation (season) Date it Occurs Angle of Insolation (Highest arc of the sun) Duration of Insolation ( daylight hours) Location of the Direct Rays (Latitude) Diagram
Maximum insolation (most)Summer
Average InsolationSpring--------------------------Autumn -------------------- ------------------------------ ----------------------------- -------------------------- ---------------------------
Minimum insolation (least) Winter
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Apparent Path of the Sun

• Aim Why do we get differing amounts of daylight
  hours during the year?

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A. Why do we get different amounts of daylight
hours during the year?

• The tilt of the Earths axis makes the sun appear
  to rise to different heights during different
  seasons.
• Summer sun rises higher, takes longer to set,
  longer daylight hours, shorter shadows, more
  intensity and duration of insolation.
• Winter sun rises lower, takes less time to set,
  shorter daylight hours, longer shadows, less
  intensity and duration of insolation.

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View of Sun in N. H. at noon
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At the equator.
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Noon sun at different latitudes
KNOW THESE DIAGRAMS!
EQUATOR
S. Hemi
N. Pole
N. Hemi
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Factors Affecting Insolation

• Intensity (strength)
• Atmosphere (clouds)
• Latitude
• Seasons
• Time of Day

• Duration (length)
• Latitude
• Season

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Surface temperatures.

• The Earths surfaces take time to absorb and heat
  the airso the warmest time of the day is late
  afternoon, even though the strongest intensity of
  insolation is at noon.
• Same applies for seasons.strongest intensity is
  in June when the sun is most direct overhead, but
  it takes a couple of months to heat the oceans
  and landso the warmest month tends to be August.

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Climate change in history Milaknovitch cycles

• Earth wobbles like a top every 26000 yrs.
• Earths orbit becomes more elliptical every
  100,000 yrs.
• Tilt changes from 23.5 to 24.5 every 41000 yrs.
• Milankovitch cycles on four different periods
  19,000, 23,000, 41,000 and 100,000 years.
• Thought to trigger ice ages

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More seasons animations

• Brainpop.com