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The Atmosphere: Composition, Structure & Temperature Earth-Sun Relationships Honors E&S 1 Earth-Sun Relationships Nearly all of the energy that drives Earth’s variable weather & climate comes from the sun o Earth intercepts only a minute percentage of the energy given off by the Sun less than one two-billionth Solar energy is not distributed evenly over Earth’s surface o Varies with latitude, time of day, and season Unequal heating of Earth creates winds and drives the ocean’s currents Variations in solar heating are caused by the motions of Earth relative to the Sun by variations in Earth’s land-sea surface Earth’s Motion Rotation is the spinning of Earth about its axis o Once every 24 hours Circle of illumination- line separating the dark half of Earth from the lighted half Revolution refers to the movement of Earth in its orbit around the Sun o Earth travels at 113,000 km/min (70,000 mph) in an elliptical orbit Seasons Long summer days expose us to more solar radiation Annual shifting of the solar angle or altitude of the Sun o Affects the amount of energy received at Earth’s surface When Sun is high in the sky the solar rays are most concentrated The lower the angle, the more spread out and less intense the solar radiation reaching the surface o Angle of the sun determines the amount of atmosphere the rays must penetrate Shultz revision of Schott ‘04 D:\769871556.doc 1 The Atmosphere: Composition, Structure & Temperature Earth-Sun Relationships Honors E&S 1 The longer the path, the greater the chances for absorption, etc. o The nearer a place is to the latitude receiving vertical rays of the Sun, the higher will be its noon Sun and the more intense will be the radiation it receives Earth’s Orientation Causes fluctuations in the Sun angle & length of daylight Earth’s axis is tilted at 23.5, called the inclination of the axis o No inclination would mean no seasons Always pointed the same direction (North Star) Solstices and Equinoxes On June 21 or 22, Earth is in a position where the axis of the northern hemisphere is tilted 23.5 toward the sun o Vertical rays strikes 23.5 N latitude Tropic of Cancer o In Northern Hemisphere = Summer Solstice On December 21 or 22, Earth is in an opposite position o Vertical rays strike 23.5 S Tropic of Capricorn o In Northern Hemisphere = Winter Solstice Equinoxes occur halfway between solstices (equal night) o September 22 or 23 = autumnal equinox o March 21 or 22 = spring equinox (vernal) o Sun’s rays are located at 0 Shultz revision of Schott ‘04 D:\769871556.doc 2