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Announcements Last math review, tonight 4-4:45pm, room 230
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When did the sun rise this morning? From what direction did the sun rise? yesterday
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N S E W When did the sun rise this morning? From what direction did the sun rise? 7:15 am 113˚
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• 76.7˚ 80.7˚• How much later (in min.) does the sun rise in Blacksburg than Williamsburg? Longitude difference = 4˚ Recall 15˚ longitude per hour 4˚/15˚ per hour = 0.267 hrs = 0.267 hrs x 60 min./hour = 16 minutes
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N S E W Local Noon For mid-latitudes in northern hemisphere sun is directly to the SOUTH At local noon the sun is at its highest angle of the day above the horizon That angle is a function of the time of year and your latitude .
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Inclination <ul><li>tilt of the Earth’s axis </li></ul><ul><li>with respect to a line perpendicular to the plane of the ecliptic </li></ul><ul><li>amount of tilt affects day length and angle of sunlight, also determines declination during solstices </li></ul>23.5 °
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Why is there a summer season? A. Summer occurs when the distance between the earth and the sun is closest B. Summer occurs when the earth’s rotational axis is tilted towards the sun, lengthening the days C. Summer occurs because the tilt of the earth’s axis makes it closer to the sun D. Summer occurs when the sun is higher overhead, so the rays strike the Earth more directly
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Seasons: the logic Summer longer days more direct sunlight more energy warmer temperatures Winter shorter days less direct sunlight less energy colder temperatures
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March 21 June 21 Sept 22 Dec 21 How does a tilt make days longer or shorter?
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1. Day length Longitude Summer Solstice Winter Solstice Autumn Equinox Spring Equinox Winter Solstice
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1. Day length Longitude Summer Solstice Winter Solstice Autumn Equinox Spring Equinox Winter Solstice <ul><li>How long is the longest day of the year (@40 o )? </li></ul>
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1. Day length Longitude Summer Solstice Winter Solstice Autumn Equinox Spring Equinox Winter Solstice <ul><li>When are the days getting shorter the fastest? </li></ul>
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2. Sun angle: declination <ul><li>Declination: The latitude for which the sun is directly overhead at noon. </li></ul>
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Seasons activity <ul><li>Divide into groups of 4 </li></ul><ul><li>Assign each member of your group a date </li></ul><ul><ul><li>- March 21, June 21, Sept 22, Dec 21 </li></ul></ul><ul><li>3. Answer following for your date </li></ul><ul><ul><li>- How is the Earth tilted relative to the Sun? </li></ul></ul><ul><ul><li>- What is the declination? </li></ul></ul><ul><ul><li>- How many hours of daylight at NP, Eq, and SP? </li></ul></ul><ul><li>Extra challenge: How would the seasons change if the tilt of the Earth was 0 °? </li></ul>
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2. Sun angle: declination curves <ul><li>graph of declination throughout year </li></ul><ul><li>x-axis: months of the year </li></ul><ul><li>y-axis: declination (90 °S to 90°N) </li></ul>
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2. Sun Angle: Insolation <ul><li>Watts per square meter (W/m 2 ) </li></ul>1 Watt 1 m 2 ? m 2 1 Watt
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2. Sun Angle X X X Y Y Y X’ X’= X/sinƟ Ɵ sinƟ=X/X’
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