GEOG 111 1st Edition Lecture 5 Outline of Last Lecture I Two components of solar radiation a Direct beam b Diffuse light II Factors of Atmospheric Transmissivity III Earth Sun Geometry Outline of Current Lecture I Earth Sun Geometry a Rotation b Revolution c Tilted axis d Solar declination e Solar elevation f Solar insolation Current Lecture I Earth Sun Geometry a Seasonal changes in earth sun geometry controls the intensity of solar radiation and the length of the day b Two independent motions affect earth sun geometry i Rotation counterclockwise West to East goes 360 degrees in 24 hours 1 This is why we have time zones 2 We go later in time to the east Europe is ahead of us and earlier in time to the west The sun rises and sets later on the western edge of a time zone region and earlier on the eastern edge of a time zone region ii Revolution the earth revolving around the sun on the plane of the ecliptic 1 Takes 365 25 days 2 Due to the earth s elliptical path not a perfect circle the distance between the earth and sun varies during the year 3 Perihelion around January 3 a Earth is closest to the sun b 147 500 000 km 4 Aphelion around July 4 a Earth is farthest away from sun b 152 500 000 km iii The Earth s axis is tilted 23 5 degrees with respect to the plane of the ecliptic 1 This results in seasons These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute iv v vi vii a Solstice December 21 22 June 21 22 i Summer longest day in Northern Hemisphere 1 SE maxed out in NH 2 SD 23 5 degrees north Tropic of Cancer 3 Latitude increases day length increases ii Winter shortest day in NH 1 SE min in NH 2 SD 23 5 degrees south Tropic of Capricorn 3 Latitude increases day length decreases b Equinox March 21 22 September 22 23 i At noon the sun will be hitting the equator directly overhead ii Equal day and equal night everywhere 12 hours iii SD 0 degrees Equator Solar declination SD latitude at which the sun s direct rays are hitting 1 Always between 23 5 degrees north Tropic of Cancer to 23 5 degrees south Tropic of Capricorn Solar elevation SE the sun s position in the sky 1 Highest in June 2 Seasonal changes in the length of the day are related to solar elevation 3 The rate of change in the day length i e sunrise and sunset time is positively related to the rate of change of solar elevation a Greatest changes late winter early spring and late summerearly fall b Smallest changes late fall early winter Links between solar radiation and earth sun geometry 1 The intensity of solar radiation is related to solar elevation a Direct rays give one energy unit b Oblique rays give half energy units 2 The intensity of solar radiation is also affected by atmospheric transmissivity which is related to the solar elevation a Solar elevation increases transmissivity increases Solar insolation SI the total amount of solar radiation energy received on a given surface area during a given time 1 Maximized in the summer and continues decreasing throughout late fall winter 2 Why is SI higher over the north polar region during the solstice The days are longer so the sun is beaming a longer amount of time even though it may not be as strong as it is in other seasons or areas This solar radiation adds up over time a If this is true why is it not warmer there The sun is coming in at a low angle so most of the radiation ends up being reflected by the snow albedo The energy is used up in melting the snow and ice and none is left to heat up the surface
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