WELCOME BACK: Procedure continued from STUDY GUIDE.
Examine the three visible satellite images. These are actual images which were obtained on or near the first days of the Northern Hemispheres fall, winter, and summer seasons. Next, examine the small drawing to the right of each Earth image. The drawing shows the relative positions of the Earth, satellite, and rays of sunlight at the time each image was recorded. (In the small drawing, the view is from above the Earths Northern Hemisphere.) If you were located on the satellite, you would have seen the same view of the Earth as shown in each accompanying satellite image.
The three Earth images were acquired when sunset was occurring at the point on the equator directly below the viewing satellite (in the center of the Earths disk). Sunset was occurring along the dashed line passing through the sub-satellite point. The arrows to the left in each image represent incoming rays of sunlight at different latitudes.
Compare the 23 September image (Image 1) with Figure 3.9 (page 33) in the Study Guide Part A: Narrative showing autumnal and vernal equinox Earth/Sun relationships. Note that in both, the sunset line and the Earths axis line up together and are oriented perpendicular to the suns rays. Because the Earth rotates once in 24 hours, the period of daylight is ______ hours everywhere except right at the poles.
Now compare the 21 December satellite image (Image 2) with Figure 3.11 (page 34) of the Narrative. On the Northern Hemispheres winter solstice, the Earths North Pole is tilted the farthest away from the sun it ever gets during the year. Consequently, from the Arctic Circle to the North Pole, the period of daylight is ____ hours. From the Antarctic Circle to the South Pole, the period of daylight is _____ hours.
Compare the 21 June satellite image (Image 3) with Figure 3.10 (page 34) of the Narrative. On the Northern Hemispheres summer solstice, the Earths North Pole is tilted towards the sun as far as it ever gets during the year. Consequently, from the Arctic Circle to the North Pole, the period of daylight is ____ hours. From the Antarctic Circle to the South Pole, the period of daylight is _____ hours.
Along with these variations in the length of daylight at various latitudes as shown in the satellite views, the intensity of incoming sunlight varies with the angle of incidence at the Earth's surface as seen in the arrows drawn for the Equator and the North (or South) Pole. (A latitude line could also be added at your latitude.) Thus, the solar energy received at a location over the course of the year depends on the solar altitude and the period of daylight.
A satellite image was not provided in this activity for the first day of the Northern Hemisphere's spring season. If it were, its solar ray orientation would look very much like the image for the first day of ______________.
As we progress through the Autumn season to the Winter Solstice and on to the next Spring season, call up DataStreme visible satellite images near times of sunrise or sunset and observe the orientation of the terminator line. Relate this "remote" view of the Earth/Sun relationship to the path of the Sun through your local sky and the length of daylight at your location. Also note the general cooling of temperatures associated with these changes in solar altitude and period of daylight. Winter happens! You might also have students call up http://www.time.gov to verify the sunrise and sunset terminator orientations and keep track of the change of length of daylight at various locations on the Earth.
To estimate amounts of solar radiation received at your location for the various months of the year similar to that given in Figure 1 of Activity 3B, you can call up http://solstice.crest.org/renewables/solrad/data/index.html. Because this site is designed to calculate the energy from solar collectors, you need to choose the option of a "flat-plate collector at 0° tilt" along with your location from the map. Finally, the energy units of kilowatt hours per square meter per day need to be multiplied by 86.04 to obtain calories per square centimeter per day as used in this activity.
After completing this week's applications, fax the following pages to your LIT mentor by Monday, October 2, 2000:
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