Horizontal sundial calculations: Difference between revisions
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Wikipedia: A [[wp:sundial|sundial]] is a device that measures time by the position of the [[wp:Sun|Sun]]. In common designs such as the horizontal sundial, the sun casts a [[wp:shadow|shadow]] from its ''style'' (also called its [[wp:Gnomon|Gnomon]], a thin rod or a sharp, straight edge)<!-- The style is the time telling edge of the gnomon, Waugh,1973 p29--> onto a flat surface marked with lines indicating the hours of the day (also called the [[wp:Sundial#Terminology|dial face]] or dial plate). As the sun moves across the sky, the shadow-edge progressively aligns with different hour-lines on the plate. Such designs rely on the style being aligned with the axis of the Earth's rotation. Hence, if such a sundial is to tell the correct time, the style must point towards [[wp:true north|true north]] (not the [[wp:North Magnetic Pole|north]] or [[wp:Magnetic South Pole|south magnetic pole]]) and the style's angle with horizontal must equal the sundial's geographical [[wp:latitude|latitude]].
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=={{header|11l}}==
{{trans|Python}}
<lang 11l>V lat = Float(input(‘Enter latitude => ’))
V lng = Float(input(‘Enter longitude => ’))
V ref = Float(input(‘Enter legal meridian => ’))
print()
V slat = sin(radians(lat))
print(‘ sine of latitude: #.3’.format(slat))
print(‘ diff longitude: #.3’.format(lng - ref))
print()
print(‘Hour, sun hour angle, dial hour line angle from 6am to 6pm’)
L(h) -6 .. 6
V hra = 15.0 * h
hra -= lng - ref
V hla = degrees(atan(slat * tan(radians(hra))))
print(‘HR=#3; HRA=#3.3; HLA=#3.3’.format(h, hra, hla))</lang>
{{out}}
<pre>
Enter latitude => -4.95
Enter longitude => -150.5
Enter legal meridian => -150
sine of latitude: -0.086
diff longitude: -0.500
Hour, sun hour angle, dial hour line angle from 6am to 6pm
HR= -6; HRA=-89.500; HLA= 84.225
HR= -5; HRA=-74.500; HLA= 17.283
HR= -4; HRA=-59.500; HLA= 8.334
HR= -3; HRA=-44.500; HLA= 4.847
HR= -2; HRA=-29.500; HLA= 2.795
HR= -1; HRA=-14.500; HLA= 1.278
HR= 0; HRA= 0.500; HLA= -0.043
HR= 1; HRA= 15.500; HLA= -1.371
HR= 2; HRA= 30.500; HLA= -2.910
HR= 3; HRA= 45.500; HLA= -5.018
HR= 4; HRA= 60.500; HLA= -8.671
HR= 5; HRA= 75.500; HLA=-18.451
HR= 6; HRA= 90.500; HLA= 84.225
</pre>
=={{header|Ada}}==
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