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.
Look at the 23 September image (Image 1). Note that the sunset line and 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.
Compare this Image 1 to the visible satellite image delivered as the Monday Activity 3A Image 1. The terminator line you drew across the Monday Image 1 visible satellite view [(was) (was not)] oriented in the same north-south direction as the dotted line on the full-disk Image 1 of 23 September.
Now look at the 21 December satellite image (Image 2). On the Northern Hemispheres winter solstice, 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.
Now look at the 21 June satellite image (Image 3). On the Northern Hemispheres summer solstice, 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, that is, the angle at which the sun's rays strike the 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 [(Fall) (Winter) (Summer)].
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 1, 2001:
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