1.16.09 Weather Maps station model- compresses weather data < temp., dew pt., pressure, etc > The Sun, the Earth and Reasons for the Seasons: The Sun: at the center of the universe average, nearly constant star so massive?extreme pressure causes heat at center, leading to nuclear fusion surface temp about 6000 º C sun ' s energy reaches us as visible light sun ' s energy is main fuel source for Earth solar wind- charged particles b lown thru space when they hit Earth ' s magnetic field and upper atmosphere ?sun spots?- (discovered by Galileo) cooler regions on sun ' s surface; 11 year cycle?could effect earth ' s climate Sun-Earth Relationships: spacially related: how, where, when and how much solar energy reaches us Earth is almost spherical rotates: once around = one day orbits: once around = one year orbit is almost circular: 150,000,000 km from sun perihelion (Earth ' s close to sun): Jan 3 aphelion (Earth ' s far from sun): July 4 Earth ' s Tilt: tilted relative to plane connecting the center of the sun and Earth (23.5 º ) effects how much solar energy reaches locations towards the sun= spring/ summer away from the sun= fall/ winter equinoxes- ?equal nights?; tilt is neither toward of away from the sun tilt causes the seasons Seasons Tropic of Capricorn- sun is strongest (our winter) Equator- sun is strongest (our spring) Tropic of Cancer- (our summer) Equator- sun ' s strongest (fall) Solar Zenith Angle: how high sun ' s in sky How to determine S.Z.A. What latitude is sun overhead at noon on a particular day? What latitude are you at? Distance of latitude (in degrees) between first and second questions = solar zenith angle EXAMPLE: What ' s noon sun at Athens, GA around June 21? noon sun lat= 34 ºN sun ' s overhead at 23.5ºN 34º-23.5º= 10.5º high in the sky (small angle) **Sun ' s always in southern sky** tilted toward sun= longer days Equator- no seasonality 30 º - 12hr/12hr seasonality 42 º - 9hr/15 hr seasonality 70 º - 24hr sunlight/summer; none in winter? most seasonality
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