Chapter 2 Solar Energy to Earth and the Seasons

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Chapter 2Solar Energy to Earth and the Seasons
Robert W. Christopherson Charlie Thomsen
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Solar Energy to Earth and the Seasons

• The Solar System, Sun, and Earth  
• Solar Energy From Sun to Earth  
• The Seasons 

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The Solar System, Sun, and Earth  

• Solar System formation and structure  
• Gravity
• Planetesimal hypothesis
• Dimensions and distances
• Speed of light
• Earths orbit

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Solar System Formation and Structure  

• Gravity
• Mutual attracting force exerted by mass on all
  other objects
• Planetesimal hypothesis
• Suns condense from nebular clouds

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Dimensions and Distances

• Speed of light
• 299,792 kmps (186,282 mps)
• Milky Way Galaxy 100,000 ly across
• Our Solar System 11 light-hours across
• Moon is 1.28 light-seconds away

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Milky Way Galaxy
Figure 2.1
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Dimensions and Distances

• Earths orbit
• Average distance from Earth to the Sun is
  150,000,000 km (93,000,000 mi)
• Perihelion closest at January 3
• 147,255,000 km (91,500,000 mi)
• Aphelion farthest at July 4
• 152,083,000 km (94,500,000 mi)
• Earth is 8 minutes 20 seconds from the Sun
• Plane of Earths orbit is the plane of the
  ecliptic

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Our Solar System
Figure 2.1
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Solar Energy From Sun to Earth  

• Solar activity and solar wind  
• Electromagnetic spectrum of radiant energy
• Intercepted energy at the top of the atmosphere 

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Solar Activity and Solar Wind

• Solar wind is clouds of electrically charged
  particles
• Sunspots are caused by magnetic storms
• Sunspots have activity cycle of 11 years

Figure 2.2
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Aurora Borealis
Figure 2.4
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The Electromagnetic Spectrum

• Sun radiates shortwave energy
• Shorter wavelengths have higher energy
• Earth radiates longwave energy

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Wavelength and Frequency
Figure 2.5
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The Electromagnetic Spectrum
Figure 2.6
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Solar and Terrestrial Energy
Figure 2.7
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Earths Energy Budget
Figure 2.8
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Distribution of Insolation

• Tropics receive more concentrated insolation due
  to Earths curvature
• Tropics receive 2.5 more than poles

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Figure 2.9
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The Seasons  

• Seasonality  
• Reasons for seasons  
• Annual march of the seasons  

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Insolation at Top of Atmosphere
Figure 2.10
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Seasonality

• Seasonal changes
• Suns altitude angle above horizon
• Declination location of the subsolar point
• Daylength

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Daily Net Radiation
Figure 2.11
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Reasons for Seasons 

• Revolution
• Rotation
• Tilt of Earths axis
• Axial parallelism
• Sphericity

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Reasons for Seasons 

• Revolution
• Earth revolves around the Sun
• Voyage takes one year
• Earths speed is 107,280 kmph (66,660 mph)
• Rotation
• Earth rotates on its axis once every 24 hours
• Rotational velocity at equator is 1674 kmph (1041
  mph)

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Revolution and Rotation
Figure 2.13
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Reasons for Seasons 

• Tilt of Earths axis
• Axis is tilted 23.5 from plane of ecliptic
• Axial parallelism
• Axis maintains alignment during orbit around the
  Sun
• North pole points toward the North Star (Polaris)
• Sphericity

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Axial Tilt and Parallelism
Figure 2.14
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Annual March of the Seasons

• Winter solstice December 21 or 22
• Subsolar point Tropic of Capricorn
• Spring equinox March 20 or 21
• Subsolar point Equator
• Summer solstice June 20 or 21
• Subsolar point Tropic of Cancer
• Fall equinox September 22 or 23
• Subsolar point Equator

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Annual March of the Seasons
Figure 2.15
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1130 P.M. in the Antarctic
Figure 2.16
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Midnight Sun
Figure 2.17
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Seasonal Observations
Figure 2.18
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End of Chapter 2

• Geosystems 7e
• An Introduction to Physical Geography