Analemma and Equation of Time

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...UNDER DEVELOPMENT...

This is a simple, SVG-based application which will generate a path-based file of the solar Equation of Time.

Results should be good to within about one second of time. But there are no corrections for temperature, latitude, solar altitude, etc.

Typing "?simpleEOT" in the URL will generate additional output using a very simple algorithm for the equation of time and associated solar declination, which takes only about ten lines of code. For individuals interested enough to compare the results of this algorithm with the more rigorous calculation displayed by default, just use your mouse to zoom in and out on the display to see the differences.

The output produced by the Export option can be used in conjunction with Inkscape, a free utility that can be installed on virtually any computer no matter what the operating system, to generate a printout which can easily be scaled to just about any size. The template for both of the concrete castings, seen to the right, were generated by the export function. The darker piece (gray cement, iron-based acid stain) was made using a clay-model/plaster-mold technique, while the more detailed white casting (white cement) was made from a rubber mold (the mold was made from a plaster model).

Stay away from INTERNET EXPLORER or the new EDGE browser on Windows 10. They will "hang" when attempting to generate the SVG export file.

? Setup

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Plot type:	EoT versus Declination EoT versus Date
Scale-X:
Scale-Y:
Year:
Calculate

? Export

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This function will allow one to export the viewport's SVG markup to an XML file which can be imported into Inkscape. It's a very quick and easy way to generate a printout which can be used as a template for construction.

Export to SVG (Inkscape)

Export to DXF

General

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• Click & Drag to move the dial around.
• Zoom using the mousewheel.
• If no mousewheel, zoom in with Alt+Click or Alt+Shift+Click.
  Zoom out with Cntl+Click (or in combo with Shift).
  Reset the entire screen by Alt+Cntl+Click.
• To examine an element on the dial graphic, simply "mouse over it". Most of the elements have an associated "tool tip" which gives some information about what is being displayed.

About

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--under development--

 

 

 

 

 

 

 

 

 

 

 

HELP : Setup

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• Year : Enter the year of interest. Note that calculations are limited to years between 2000 and 2050.

• EoT vs. Declination : This will produce the familiar analemma.

• EoT vs. Date : This choice will plot the equation of time versus the calendar date.

• Scale-X & Scale-Y : Use these values to adjust the height and width of the generated output.

HELP : Pan Dial Input

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This function allows one to observe the effect of altering a single dial setting (e.g. wall declination, latitude, length of gnomon, etc) without having to open up the setup dialog. The user can quickly increment or decrement the chosen setting by the amount specified and observe the effect on the dial display.

If you open the setup dialog in conjunction with this operation, you can keep track of the current input settings, which are automatically updated.

The variables do NOT have preset ranges. The code will attempt to produce a dial no matter what you input. There isn't a lot of error checking. If the page stops working and you think the inputs are reasonable, trying reloading the page (you'll have to re-enter the inputs). If that doesn't work, post a comment and I will see if there is a bug somewhere.

HELP : Extras

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Hour Lines

In the past, some civilizations and cultures considered the start of the day, and hence the first hour of the day, to coincide with sunrise (Babylonians), while others (the Romans, or Italians) ended the day at sunset, which also meant that for counting purposes, the first hour of the new day began at sunset.

Babylonian hour lines indicate the number of hours the sun has been above the horizon, or the number of hours that have elapsed since sunrise.

Italian hour lines indicate the number of hours of sunlight left in the day, or the number of hours until sunset.

HELP : Export

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• You can use this SVG file, in conjunction with Inkscape, to generate a graphical printout of the Equation of Time. If you are unfamiliar with Inkscape, try this short tutorial to see how its done.
• Saving the File to Disk

  Because this application runs inside a browser, it is somewhat limited in terms of its ability to perform routine file operations on a user's computer.

  Select all the text displayed in the export text window and paste it into an ASCII text editor (e.g. "Notepad"), then save it on your computer giving it whatever name you choose, with a file extension of SVG (NOTE: make sure there are no blank lines at the beginning of the file).

• Adjustments for Paper Size & Units

  The SVG document has been formatted for use with Inkscape for the purpose of printing an image of the SVG graphic to scale. It assumes you will be printing on 8½ × 11" paper (i.e. standard "letter" paper size) and that the units used for the dial are inches (i.e. the numerical value for the length of the gnomon represents inches). To change the default setting, you can either edit the text yourself using the following instructions, or select the appropriate radio button to the right. NOTE: Make the appropriate selection after generating the SVG file.

  • PAPER
  • Letter
  • Legal
  • A4

  • UNITS
  • Inches
  • Centimeters

  • If you are using legal-size paper, change the height and viewbox parameters to read: height='1260' and viewbox='0 0 765 1260'.
  • If you are using A4 paper size, change the width, height and viewbox parameters to read: width='744', height='1052' and viewbox='0 0 744 1052'.
  • If you are using units of centimeters instead of inches, you will need to edit the parameter transform='matrix(90,0,0,-90,0,0)' to read: transform='matrix(35.433,0,0,-35.433,0,0)'.

  In time I intend to handle the conversion to other paper sizes and units programmatically, but right now I'm in a hurry and am concentrating on just getting the routine in place and a series of instructions written for how to use it in conjunction with Inkscape .... March 2011, BH.

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