Exercise 12

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Exercise 12 Pg. 173 Earth Sun Relations
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Weather

• The state of the atmosphere at a particular place
  for a short period of time.
• Described by measuring the four basic elements
  temperature, moisture, air pressure, and wind
  (direction and velocity).

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Temperature

• Most important variable it controls the other
  variables.
• Example cool air high pressure system, and warm
  air low pressure system.
• Earth is heated from the Sun.

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Solar Heat

• Intensity - the angle at which the rays strike
  the surface of the Earth.
• Duration- number of hours of daylight in a 24
  hour period.
• They both will determine the amount of solar
  radiation any place on Earth will receive.

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Ray Diagram on Pg 174

• The angle from the Sun to point A is 90O. The
  sun beam projected will cover an area of 10mm.
• If the angle from the Sun to point B is 30O. The
  sun beam projected will cover an area of 17mm.
• Thus the rays hitting point A are concentrated in
  a smaller area thus are Stronger

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Solar Radiation

• Why is it warmer at the equator?
• The greater the angle the stronger the intensity.
• Tropic of Cancer 23.5 N Lat.
• Tropic of Capricorn 23.5 S Lat.

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Solar radiation would be constant if it were not
for

• The Earths rotates on its axis on a 23.50 and
  revolves around the Sun
• Throughout the year the Earths axis is pointed
  to the same place.
• The Earth rotates counter clockwise
• One whole revolution 24 hours.
• If the Earth was not titled then we would not
  have seasons.

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Days of the year

• Summer Solstice (ours June 20-22) longest day
  of the year the day with the greatest number of
  hours of daylight.
• Winter Solstice (ours Dec 21) shortest day of
  the year because it is the day with the least
  hours of daylight.

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Circle of Illumination

• This is what gives us darkness at night and light
  during the day.
• Arctic circle 66.5 ON Latitude
• Antarctic circle 66.5 OS Latitude
• Both have 24 hours with and without sun.

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Equinox

• Rays of the Sun are migrating between the Tropic
  of Cancer and the Tropic of Capricorn.
• At this time rays of the Sun are vertical at the
  equator.
• Equal hours of darkness and light (12 hours)
• This occurs Mar 21-22 and Sept 22-23

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Solstice 1

• June 20-22
• For us this is the Summer Solstice.
• Rays of the Sun are directed toward the Tropic
  of Cancer. The rays hit this area at 90O.
• If we lived below the equator then it would be
  the Winter Solstice.
• Because of the tilt, more solar intensity hits
  the tropic of Cancer and less at the tropic of
  Capricorn.
• Circle of illumination South pole 0 hrs of sun
  and North pole 24 hours of sun.

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Equinox

• Suns rays hitting Equator at 90O angle
• Less at both tropics
• First day of spring and fall.
• March 21 - 22 and Sept. 21 - 22
• Circle of illumination cuts through the poles,
  thus 12 hours of light and dark at the poles.

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Solstice 2

• Dec. 20-22
• For us this is the Winter Solstice.
• Rays of the are directed toward the Tropic of
  Capricorn. The rays hit this area at 90O.
• At this time the rays hit the equator at less
  then 90O.
• The rays hit the Tropic of Cancer at a smaller
  angle.
• Remember the greater the angle the stronger the
  intensity.
• Circle of illumination N pole 0 hrs of sun and
  South 24 hours of sun.

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The Sun is Directly Overhead
Tropic of Cancer 23.5O N Lat. Overhead on June 21

Equator 0O Lat. Overhead Mar 21 and Sept. 21
Tropic of Capricorn 23.5O S Lat. Overhead Dec. 21

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Analemma Figure 12.6 pg 177

• Tells us where the sun is overhead at noon time
  in the world.
• Used for navigation before GPS.
• Nov.4 the sun is overhead at noon time at 15O S
  Latitude
• Today April 14 9O N Latitude

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Chapter Summary pg 181

• Questions 4, 5, 6, 7 11