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daylight anddarkness
2 – preparat i on
DAYLIGHTANDDARKNESS (AIPGEN 2.7)
‘Night’ is that periodbetween the end of the evening civil twilight and the
beginningof themorning civil twilight. For all intents anpurposes, first light
should be construed as the beginningof civil twilight and last light as the end
of civil twilight. The terms ‘sunrise’ and ‘sunset’ have no relevancewhen
calculating day light operating times for theVFR pilot.
To compute the beginning or end of daylight using the graphs contained in
this section:
• enter the top or bottom of the scale at the appropriate date;
• move vertically up or down to the curve for the latitude of theplace
concerned (interpolating for intermediate latitudes if necessary);
• move horizontally to the left or to the right and read local mean time on
the vertical scale at the side;
• to convert toUTC, subtract (inE longitudes) from the LMTobtained, the
time increment corresponding to the longitude of theplace concerned in
the ‘Conversion of Arc toTime’ table.
• to convert toEST, add 10 hours toUTC;
• to convert toCST, add 9.5hours toUTC; and
• to convert toWST, add8 hours toUTC.
Example:
To determine the end of daylight at Echuca (S3609.0E14446.0)
on 20thNovember. Using the graph, enter at 20thNovember
at the top of the page and follow downwards to latitude 36° (by
interpolation), then horizontally to the left and readoff LMT=
1919. To convert toUTC, obtain theArc of time by entering the
‘Conversion of Arc to Time’ table, at longitude 144° (9hours 36
minutes). Add the increment corresponding to46’ in the right hand
column= 3’04’ + 0936= 0939
Subtract this from the LMT found: 1919 – 0939= 0940UTC.
To findEST add 10 hours toUTC=1940EST.
Users of these graphs should note that the parameters used in compiling
theDaylight andDarknessGraphs do not include thenatureof the terrain
surrounding a location, or the presence of other than a cloudless sky and
unlimited visibility at that location.