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Required Parameters
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SCALE OF THE
SUNDIAL
DIMENSIONS OF THE SUNDIAL
A sundial should be sized for easy reading of the dial. A larger sundial can have a greater number of hour lines for more precision and the lines can be more widely spaced for easier reading. A larger size also allows for easier reading from a distance.
The program, because it is independent of the drawing scale, can design clocks with a span of several meters (yards) without any difficulty. With direct printing from Windows, the size limitation is about 3 meters (9 feet). Larger sundials can be printed by outputting in DXF format to a CAD (Computer Aided Drawing) software program.
ORIENTATION
(DECLINATION) OF THE WALL
The orientation is the angle that the wall makes with a true north-south local meridian for the location of the
sundial.
There are two methods used to determine the orientation of a wall:
1. The first and simplest method is to use a magnetic compass to find true magnetic
north-south and make the necessary correction to obtain true geographical
north-south using a tabulated magnetic declination value for the location. This method is only used if a minimum of accuracy is
desired.
2. The second and more preferred method is to use a vertical plumb line to cast a true
north-south meridian when the sun is at its highest position during the day. This method or similar ones using surveying instruments are precise if done
correctly. Several other methods of finding the orientation of a wall are available from a good bibliographical source or the
internet. In the program, this parameter is input in the screen
Orientation of the wall.
To determine the exact time that the sun reaches its highest point (crosses the meridian) the following chart can be used. The chart is referenced for the Greenwich meridian (zero degree) and must be adjusted for the actual longitude of the sundial. Four (4) minutes must be added for each degree of longitude west of Greenwich and likewise subtracted for each degree east of Greenwich. Daylight savings time, if in effect, must also be accounted for (spring ahead 1hrfall back 1hr). For dates between those listed in the table a linear interpolation can be used.
JANUARY
Day 10 12h07m
Day 20 12h10m
Day 30 12h13m
FEBRUARY
Day 10 12h14m
Day 20 12h13m
Day 29 12h12m
MARCH
Day 10 12h10m
Day 20 12h07m
Day 30 12h04m
APRIL
Day 10 12h01m
Day 20 11h58m
Day 30 11h57m
MAY
Day 10 11h56m
Day 20 11h56m
Day 30 11h57m
JUNE
Day 10 11h59m
Day 20 12h01m
Day 30 12h03m
JULY
Day 10 12h05m
Day 20 12h06m
Day 30 12h06m
AUGUST
Day 10 12h05m
Day 20 12h03m
Day 30 12h00m
SEPTEMBER
Day 10 11h57m
Day 20 11h53m
Day 30 11h50m
OCTOBER
Day 10 11h47m
Day 20 11h45m
Day 30 11h44m
NOVEMBER
Day 10 11h44m
Day 20 11h46m
Day 30 11h49m
DECEMBER
Day 10 11h53m
Day 20 11h58m
Day 30 12h03m
TABLE OF TIME ECUATION CORRECTIONS
The next table shows the time corrections the observer should apply in order to obtain the Civil Time in a sundial without Time Ecuation correction. It has been made for days 5,15 and 25 of each month, so if you need the correction for other day just simply interpolate.
Time Ec. day 5 day 15 day 25 January -5m03 -9m10 -12m12 February -14m01 -14m16 -13m18 March -11m45 -9m13 -6m16 Apryl -2m57 +0m14 +1m56 May +3m18 +3m44 +3m16 June +1m46 -0m10 -2m20 July -4m19 -5m46 -6m24 Augost -5m59 -4m33 -2m14 September +1m05 +4m32 +8m04 October +11m20 +14m01 +15m47 November +16m22 +15m28 +13m11 December +9m38 +5m09 +0m13