
Daylight() is a program which calculates sunrise, sunset and daylight times for any
location on the Earth. The Sun's declination and culmination are also calculated.
The sunset is calculated for the moment when the Sun's upper limb touches the horizon.
The atmospheric refraction is also accounted for (both contribute -50' or -.833 degree 
under the horizon). 

				DATA REPRESENTATIONS

The data can be displayed in four different representations:

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1st key	  2nd key	Rewiev of data:
------------------------ ------------------------------------------------------------
F1					DATA FOR THE DAY
			date, sunrise, sunset and daylight times for one day
			prolongation of the daylight from the shortest daylight
			the same in % (100% is the difference between the shortest
				and the longest daylight)
			Sun's culmination time and angle (in degrees; angle < 0
				means that the Sun's culmination is under the horizon)
			Sun's declination (in degrees)
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F2					DATA FOR THE WEEK
			date, sunrise, sunset and daylight times for seven days
-------------------------------------------------------------------------------------
F3					DATA FOR TWO SYMETRICAL DAYS
			date, sunrise, sunset and daylight times for symetrical days
				(days with similar daylight times)
			number of the days between these dates
-------------------------------------------------------------------------------------
F4					DATA FOR TWO GIVEN DAYS
			date, sunrise, sunset, daylight times for two given days
			time differences between these days
			the same in % (100% is the difference between the shortest
				and the longest daylight)
			number of the days between these dates
-------------------------------------------------------------------------------------

Every rewiev (F1...F4) requires enter of the date in the format day.month 
	(for example 31.12).
Time format is hours:minutes (for example 22:12). 
Time --:-- means that the Sun is continuously below the horizon (Polar night). 
Time **:** means that the Sun is continuously above the horizon (Midnight Sun). 
Time < 0:00 means that the event happens the day before 
	(for example -0:07 = day before at 23:53). 
Time > 24:00 means that the event happens the day after 
	(for example 24:34 = day after at 00:34).

				   OTHER COMMANDS

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1st key	  2nd key	Command
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F5			Parameters
			Longitude (in degrees; +=East, -=West; for example -23.4 or
				-2324', - must be unary minus (-) ), 
			Latitude  (in degrees; +=North, -=South) and 
			Time correction for local time (in minutes; 
				it can be 0, +-30, +-60,...).
2nd	  F1		Rewiev of the commands
+			one day forward
-			one day back
right			one week forward
left			one week back
up			one month forward
down			one month back
2nd	  +		second date one day forward   (only within command F4)
2nd	  -		second date one day back      (          "           )
2nd	  right		second date one week forward  (          "           )
2nd	  left		second date one week back     (          "           )
2nd	  up		second date one month forward (          "           )
2nd	  down		second date one month back    (          "           )
2nd	  APPS		exchange 1st and 2nd date
HOME			exit (or 2nd ESC)
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			TIME CALCULATION AND TIME CORRECTION

The time is calculated from the longitude and Greenwich Mean Time. Only if the local
time differentiates from the next table, time correction value (in minutes) for this 
difference must be set (command F5). Daylight saving time is not considered.

------------------------------------------------------------------------------------
longitude (W)		time			longitude (E)		time
------------------------------------------------------------------------------------
   0 +-7.5		GMT			  0 +-7.5		GMT
 -15 +-7.5		GMT-1h			 15 +-7.5		GMT+1h
 -30 +-7.5		GMT-2h			 30 +-7.5		GMT+2h
 -45 +-7.5		GMT-3h			 45 +-7.5		GMT+3h
 -60 +-7.5		GMT-4h			 60 +-7.5		GMT+4h
 -75 +-7.5		GMT-5h			 75 +-7.5		GMT+5h
 -90 +-7.5		GMT-6h			 90 +-7.5		GMT+6h
-105 +-7.5		GMT-7h			105 +-7.5		GMT+7h
-120 +-7.5		GMT-8h			120 +-7.5		GMT+8h
-135 +-7.5		GMT-9h			135 +-7.5		GMT+9h
-150 +-7.5		GMT-10h			150 +-7.5		GMT+10h
-165 +-7.5		GMT-11h			165 +-7.5		GMT+11h
-180 +-7.5		GMT-12h			180 +-7.5		GMT+12h
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Some examples for the calculation of the time correction:

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Place	    Country     Longitude   Time from Long.  Local time    Time corr.(min.)
-----------------------------------------------------------------------------------
Sydney	    Australia	 151.5	     GMT+10h	      GMT+10h		   0
Calcutta    India	  88.	     GMT+6h	      GMT+5.5h		 -30
New Delhi   India	  77.	     GMT+5h	      GMT+5.5h		 +30
Ljubljana   Slovenia	  14.5	     GMT+1h	      GMT+1h		   0
Paris	    France	   2.3	     GMT	      GMT+1h		 +60
New York    USA		 -74.	     GMT-5h	      GMT-5h		   0
Nome	    Alaska	-165.	     GMT-11h	      GMT-9h		+120
-----------------------------------------------------------------------------------

				      ACCURACY

Calculations are based on average year cycle with 365 days with the corrections for
each year. Stated accuracy will be preserved for some decades. Leap years are included
in 4 years average, but the data for the 29th February are not calculated. They lie 
between the data for 28th February and 1st March.

Average	deviation		Remark  
+- 0 ... 0.8 day              	in the year cycle
+- 0 ... 2 minutes		sunrise/sunset times, -65 <= latitude <= 65
+- 0 ... 0.2 degree		culmination, declination

On the greater latitudes the accuracy falls with the growth of the latitude, specially
near the beginning or the end of the Midnight Sun or of the Polar night. In these 
periods the deviation of the sunset/sunrise times can be up to +-1 hour. Because of 
this reason (the shortest daylight can last only some minutes) the beginning and the 
end of the Midnight Sun and of the Polar night is calculated with deviation +- 1 day.

				      REMARKS

Operational system version 2.08 is required.

Reference for exact computations: http://aa.usno.navy.mil
(Data services, Table of Sunrise/Sunset for an entire year)


Primoz Pirnat



