To construct a 24-hour clock to be used as a pie graph to show daylight hours versus nighttime hours.
This will depend on how many graphs the students are constructing. To construct one graph will take about 20 minutes. If you are comparing a number of different dates for your area or you are comparing the daylight hours at a number of different latitudes, you will probably want to reproduce a line drawing of the basic graph.
- Help each student construct a pie graph using a compass to draw the circle and a ruler and protractor to divide the circle into twenty-four wedges. Divide each wedge in half and then each half in half again by making tick marks on the circle. Mark the lines dividing the twenty-four wedges from 1 through 24 to make a 24-hour clock. Alternatively, hand out a basic pie graph already constructed as described and reproduced in quantity.
- On each graph, ask the students to plot the time of sunrise and sunset for a certain day at a certain latitude to the nearest quarter of an hour. Have the students color the dark hours and the light hours the same contrasting colors on all the graphs.
- Either assign data for different dates or latitudes to each student or group of students, or have all the students color in several different sets of data on already-prepared graphs. Be sure to assign dates at diametrically opposite times of year or assign latitudes for the same date in areas north and south of the equator. (This information can be obtained from an ephemeris.)
- After a variety of graphs are prepared, compare the areas of light and dark on graphs for the different dates or different areas.
If the students are contrasting daylight and nighttime hours at different times of year, they will see graphically that the longest days are in June and the shortest in December and that the hours of daylight and darkness are equal at the equinoxes.
If the students are contrasting the length of daylight hours at different latitudes, they will find that in June the daylight hours are longer than the hours of darkness north of the equator and shorter south of the equator. On any given date, the daylight hours and hours of darkness get closer to being equal as you approach the equator. In areas along the equator, the days and nights are of equal length year around.
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