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Unit 4: Sun-Earth Relationships. Revolution Rotation Declination (Tilt of Earth’s Axis) Seasons Time Zones Insolation and its variation. Sunrise over the Earth. Source: http://ajorbahman.blogspot.com/2011/02/third-of-russians-think-sun-spins-round.html. OBJECTIVES
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Unit 4: Sun-Earth Relationships • Revolution • Rotation • Declination (Tilt of Earth’s Axis) • Seasons • Time Zones • Insolation and its variation Sunrise over the Earth. Source: http://ajorbahman.blogspot.com/2011/02/third-of-russians-think-sun-spins-round.html
OBJECTIVES • Examine the Earth’s motions relative to the Sun • Demonstrate the consequences of the Earth’s axis tilt for the annual march of the seasons • Introduce the time and spatial variations in solar radiation received at surface locations
Revolution of the Earth around the Sun • Perihelion-closest to Sun Jan. 3rd • Aphelion-farthest from Sun July 4th • Distance differences from Sun do not influence amount of solar energy received significantly Earth revolves around the Sun in an elliptical path. Earth and Sun are not drawn to scale, and the orbit’s elongation is highly exaggerated for clarity.
Counterclockwise movements • Revolution-annual cycle • Rotation-daily cycle
Declination of the Earth’s Axis • Constant tilt of 23.5 degrees • Provides seasons Video shows misconceptions about the cause of the seasons. http://www.youtube.com/watch?v=iMEfYLvxioc
Midnight Sun: Within the Arctic and Antarctic Circle the Sun does not set at Summer Solstice
Solar altitude-Sun’s height above the horizon • Vertical (90o) Sun is at the equator on equinoxes • Vertical Sun is at the Tropic of Cancer on summer solstice • Vertical Sun is at the Tropic of Capricorn on winter solstice
World’s Time Zones Source: http://www.colourbox.com/vector/clocks-in-people-head-vector-invitation-card-vector-3095601 Why are the boundaries not straight lines? Why are the Prime Meridian, International Dateline significant?
Intensity of Sunlight Source: http://nsidc.org/cryosphere/frozenground/what_affects_fg.html Reception of solar radiation at different latitudes showing direct, indirect rays
Relationship between solar noon altitude and daylight hours Daylength (left axis) and noon solar altitude (right axis) at 45° north latitude. These factors work together in producing pronounced seasonality at middle and high latitudes. Notice also how the pace of change in both is much greater near the equinoxes than near the depths of summer and winter.
Spatial distribution of insolation at top of the atmosphere as percentage of global average Verify we have permission for this image Seasonal and spatial variation in solar radiation reaching the top of the atmosphere as a percentage of the global average. The latitude axis is scaled to acount for shrinking area at higher latitudes. Compare with patterns of the previous figures to see how solar position modulates the effect of daylength.