Name:____________________________________ Date:_______________________ Sunshine Daylight follows a dark night. - Massai Proverb Key concepts in this lab: Earth/Sun Geometry Insolation Sun Angle Daylength Solar Declination Analemma Circle of illumination Tangent Rays Introduction: Radiation emitted from the sun travels through outer space at 300,000,000 meters per second (3.0 x 108 ms-1). Earth/sun geometry determines how much solar energy strikes the planet. Insolation is the amount of solar energy that strikes a given location on the planet’s surface and varies seasonally due to changes in sun angle and daylength. The sun can only directly strike locations at one parallel of latitude on a given day. This latitude is known as the solar declination. We can use a special diagram called analemma to tell us the solar declination on each day of the year. We can then use this information to calculate the sun angle at any latitude on a given day using the following equations: Arc Distance = latitudinal distance between location of interest and the solar declination Sun angle = 90 – arc distance The Circle of Illumination divides the earth into two halves: the illuminated side (day) and the dark side (night). We experience day and night as our location on the earth spins out of one half and into the other. Daylength varies each day of the year at all latitudes except at the equator. Here in Kentucky, we experience longer days when the northern hemisphere is pointed toward the sun and shorter days when our hemisphere is pointed away. The difference between the number of daylight hours during summer and winter gets larger as one moves further north or south of the equator. The latitudes where the circle of illumination touches the planet are the latitudes of the tangent rays. Areas between the tangent rays and the poles experience 24 hours of daylight and 24 hours of darkness during part of the year. We can calculate the latitude of the tangent rays on any day using the following equation: Tangent rays = 90 – solar declination Part 1: Fill in the table below. Richmond’s latitude is 37.74°N. Day Solar Declination Sun angle at the equator Sun angle in Richmond, KY Sun angle at the Arctic Circle January 3rd March 17th May 30th November 26th Part 2: Fill in the table below. Day Solar Declination Tangent Rays (latitude) 24 hours day or night at North pole 24 hours day or night at South pole February 20th June 8th October 5th December 25th Part 3: Use the information provided on the first page of this lab to answer the questions below. Be sure to show your work on mathematical problems and circle your final answer. 1.) How long does it take energy emitted from the surface of the sun to reach the earth? (Assume an average earth/sun distance of 150 million kilometers.) Write your final answer as __ minutes and __ seconds. 2.) a. What is the shortest day of the year here in Richmond, KY? b. What is the shortest day of the year in Maputo, Mozambique? 3.) a. On what day does the sun get the highest above the horizon here in Richmond, KY? b. On what day does the sun get the highest above the horizon in Maseru, Lesotho? 4.) a. What degree of latitude would you have to go to in order to see the sun directly overhead at noon on the 4th of July? b. Name a country that is located along this parallel of latitude. 5.) a. There is a huge 24-hour party to celebrate Dr. Yow’s birthday on August 3rd at the southernmost latitude that experiences 24 hours of daylight on this day. What latitude would you have to go to if you wanted to go to the party? b. If you were worn out from the festivities on the 3rd and needed a lot of sleep, what degree of latitude would you have to go to in order to experience 24 hours of darkness on August 4th? Part 4: Critical Thinking 1.) Daylength and sun angle determine daily insolatoion. Which of these two factors do you think is most important in determining how much solar energy a place receives on a given day. Explain your answer using 1-3 complete sentences. Bonus Question: The opening quote on this lab was a Massai Proverb. For 5 extra points, do an internet search to find out who the Massai are and where they live? List 5 things about them and the source of your information.
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