created by Carl Sabanski
When you have decided what type of sundial you want to design and build, then there a few details that you need to deal with. Some of this information is required to design certain sundials, some to be able to set it up once it is built and others will increase the accuracy of the time indicted by the sundial. This section deals with a number of these topics.
First you must determine the geographical location where the sundial is will be placed. For a sundial that will indicate local apparent time you require the latitude. It the dial is not located on the central meridian of the time zone and you wish to correct for this, you will need to know the longitude. There are sections that discuss longitude and latitude and how to apply longitude correction. Also if you have a sundial that was designed and built for a different latitude there is a section that shows you how to correct for this during the installation of the sundial.
You also need to determine how high the gnomon of the sundial must be to ensure that the shadow reaches the hour markers during the entire year. If you are including hour lines for all the time intervals to be indicated, this may not be as important because you can use the lines to help determine the time. If you wish to include declination lines on the dial plate, then you require a nodus and its position is critical to ensure that the shadow follows these lines accurately. There is a section that deals with determining the minimum shadow length you gnomon will cast and how long the style must be to deliver a shadow of predetermined length.
If the gnomon of your sundial has a significant width, an error will be introduced if you do not adjust the positioning of the hour lines to account for this. This is due to the fact that the shadow will be cast from a different edge as the day progresses from morning to night. An edge change will occur three times throughout the day. Correcting for a wide gnomon is simple and a section discusses this in detail.
To install your sundial you need to know where True North (South) is located as the gnomon must point directly to the Celestial Pole. A section discusses methods of determining this.
In time more topics will be presented that may be of use to you in you quest to build an accurate sundial.