Capricorn: Dec.22-Jan.29 The Sundial Primer
created by Carl Sabanski
Capricorn: Dec.22-Jan.29

The Sundial Primer Index

DeltaCad Sundial Macros - Valentin Hristov - Universal Ring Sundial

The universal ring sundial is a modified equatorial sundial that can be used anywhere in the world. The elegant paper design was described by Wee-Meng Lee in 2005 on his web page http://leewm.freeshell.org/origami/ (Click on the picture for the pdf file!!!). In 2006 Valentin Hristov converted the idea into a DeltaCad macro adding the rotation of the hour ring which allows for corrections for the longitude and the Equation of Time

Universal Ring Sundial - sdring

The universal ring sundial macro requires no inputs from the user. The sundial drawn with this macro is shown in Figure 1.

Figure 1 - Universal Ring Sundial

Figure 1 - Universal Ring Sundial

The entire sundial can be printed to fit on a single "Letter" or "A4" sheet of paper but the parts are quite small. If each of the 3 main rings is printed separately at full scale the size of the sundial then becomes larger and it is easier to build. Keep the two rectangular pieces with the ring they are near when printing. Choose "Set Print Region" in the File menu of DeltaCad. "Print Area" has as a possibility "Set to Current Window". Keeping the same suitable scale you can show fully on the screen one of the three rings at a time and print it. Another possibility is to give a rectangle for printing. Suitable values (square areas) are:

Left/Right/Bottom/Top: North Face: -3.5/3.5/-3.5/3.5; South Face -3.5/3.5/3.5/10.5; Latitude Ring: 0.5/7.5/0/7

The photograph in Figure 2 shows the parts of this sundial. There are 4 main parts: 

1. Latitude ring (with Longitude correction)
2. Celestial north facing hour ring (with EOT correction table)
3. Celestial south facing hour ring (with glue tabs)
4. Date slider

The remaining two rectangular pieces are used to hold the rings perpendicular to each other when the sundial is in use.

Figure 2: Cut out the model and fold carefully.

Figure 2: Cut out the model and fold carefully.

The double ring at the bottom left can be cut out using a craft knife. Be very careful not to cut the short dashed lines used to make the hinges for the latitude ring and the date scale. Once the parts are cut out the sundial is very easy to assemble.

Figure 3 illustrate the next two steps involved in the assembly of this sundial.

Figure 3: Step 1

 Step 1: Place south facing hour ring face down. Place latitude ring on hour ring face up.

Figure 3: Step 2

Step 2: Glue north facing hour ring face up to tabs.

Figure 3: Assembling the Universal Ring Sundial

When performing Step 2 be very careful not to glue a tab to the latitude ring. Do not apply too much glue to the tabs or the latitude ring may become glued to an hour ring. The latitude ring must be able to turn between the two hour rings.

The final step is to fold the date slider on the date scale. Position it on the back of the date scale with the pointers on the front to allow for easy selection of the date. Ensure the aperture (hole) is aligned with the slot in the date scale and the slider can be moved up and down. Figure 4 shows the completed sundial.

Figure 4: Universal Ring Sundial Model

Figure 4: Universal Ring Sundial Model

HOW TO USE THE SUNDIAL

  • If the sundial is to show local apparent or solar time rotate the latitude ring until the 0 or Central Meridian Line is aligned with the 0 line on the EoT graph. In any case this is the first step in setting up the sundial.

  • If the sundial is to indicate zonal solar time, local apparent or solar time with longitude correction, rotate the latitude ring until the 0 line on the EoT graph is aligned with the correct longitude value east or west of the Central Meridian. If the sundial is to indicate clock time this step must be completed. In addition, make a pencil mark on the latitude ring at the point of the 0 line on the EoT graph. A pencil mark can also be placed at the desired latitude.

  • If the sundial is to indicate clock time you must correct for the Equation of Time. Knowing the date find the point where the date line on the graph intersects the EoT curve. This point will give the direction and position the pencil mark on the latitude ring must be rotated to.

  • No correction must be made for Daylight Saving time. The hour lines have a second set of numbers to account for this.

  • Move the date slider until it points to the correct date.

  • The sundial has been corrected for longitude and the Equation of Time. It has also been set for the date and is ready for use.

  • Rotate the latitude ring on its hinges until it is perpendicular to the hour rings. Use the two rectangular pieces to hold it in position.

  • Suspend the sundial from the latitude ring at the position of your latitude. A paper clip and some string is one method to use.

  • Turn the sundial and rotate the date scale on its hinges until a spot of light appears on the hour ring. This happens at two places because twice a day the sun has the same altitude (elevation, height), once before LOCAL NOON and a second time after it. Make the correct time choice and then during the entire day the sunlight will be on a cone with the vertex being  the aperture (hole) and the base being the hour ring.

  • The indicated time is clock or civil time at your location.

Figure 5 shows the sundial set up and ready to use. The two rectangular pieces are folded around the latitude ring and locked in place using the short horizontal cuts. It can be seen how the tabs from these two pieces help to hold the latitude ring and hour ring perpendicular to each other. They should be opened slightly. The tabs can be folded to allow the sundial to be folded flat. A paper clip and string are positioned at the sundial's latitude and used to suspend the sundial at the correct angle. 

Figure 5: Universal Ring Sundial Model Ready for Use

Figure 5: Universal Ring Sundial Model Ready for Use