NAVAL AIR STATION NORFOLK VA
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The daylighter is a device which can conveniently illustrate the duration of daylight, twilight, and darkness, particularly in moderately high latitudes. The simpler situations at low latitudes are familiar, as is the annual cycle exactly at the poles. For normal use, the daylighter is set up by placing an overlay map, Northern or Southern Hemisphere, so that it will pivot about the pole over a daylight pattern selected for the appropriate hemisphere and for the date. Daylight patterns are prepared for a number f values of declination of the sun. Except for the soltice patterns, the sun reaches each declination on two dates of each year, once as it passes northward and once as it passes southward.