November 2, 2025
Description
The original design of the “Sunquest” sundial was derived from a traditional armillary sphere, featuring an axis parallel to that of the Earth and multiple nested rings representing latitude, longitude, the celestial equator, the ecliptic, and more. The gnomon design presented here is a simplified/alternate version of the original Schmoyer gnomon, as described in the 1959 Scientific American article; (see references below). It also doesn't have an adjustment for longitude offsets from the Standard Time meridians, or Daylight Savings Time (DST) like the original design.
Update (02-08-25): The numerals on the latitude crescent were changed to properly represent the observers actual latitude vs. the anti-latitude. Look for the file named: sunquest_latitude_scale_crescent_v2 If you you prefer to keep using your original latitude crescent, you will need to substract 90 degrees from your actual latitude & use this number to set your sundial's latitude scale. Example: 90 - observers latitude (50 degrees) = 40 degrees ← set the latitude crescent reading to this number.
Update (05-01-24): Added support for both northern & southern hemispheres. If you live in the southern hemisphere, make sure to use the southern hemisphere dial plate & gnomon holders, which labels the correct seasons for the corresponding months on the gnomon. The analemma gnomon itself is the same design for north or south hemispheres. You just need to rotate the analemma gnomon end-for-end by 180 degrees so that the narrow part of the curve is pointing towards the top portion of the sundial. Refer to the assembly instructions for clarification.
Figure 1: The original Sunquest Sundial by Richard L. Schmoyer, 1959, as featured in Scientific American.
The original Sunquest was constructed out of brass or aluminum foundry castings & was offered assembled or in kit form. It consisted of the following components:
From Schmoyer's original article: “The Sunquest gnomon is related to the analemma but differs in that the halves of the figure are separated. Structurally, the curves for each half-year are placed at right angles to each other, with the apex of the angle opened to form a narrow slot. The halves of the gnomon are bent into compound curves so that their shadow-making edges are complementary. They are almost, but not quite, asymmetrical since the sun-time to clock-time correction for the two half-years differs. It is essentially an analemma. When either half is turned to face the sun, a curved ribbon of sunlight passes through the slot, intersects the time scale, and corresponds with the Equation of Time for that half of the year; the remaining six months are represented by the other half. Unlike the familiar garden sundial, where time is indicated by a shadow or the edge of a shadow, the Sunquest sundial shows time by a band of sunlight between two shadows cast by the gnomon on the time scale.”
Richard Kellogg also describes his process of implementing a 3D printable version of the original Schomoyer sundial on the North American Sundial Society (NASS) website. Check out his articles: 3D-Printed Schmoyer Sundial
For useful background information on analemmatic sundials in general; i.e. history, theory of operation, design, how to align and use, etc. refer to this useful printable: Heliochronometer - World's Most Accurate Sundial by yba2cuo3 | Download free STL model | Printables.com
This sundial was constructed out of ABS plastic filament. Check the Technical Details section & How was the Analemma Curve Designed into this Heliochronometer from this other printable: Heliochronometer - World's Most Accurate Sundial by yba2cuo3 | Download free STL model | Printables.com The analemma curve was calculated & plotted using MS Excel and then scaled to match the size (diameter) of this equatorial sundial.
If you prefer using an alternative to the rotatable two-faced analemma presented in this Schmoyer Equatorial - Analemmatic sundial design, you can download a 3D analemma which doesn't require any rotation or alignment to accurately display the time. You just need to read the appropriate shadow edge against the main dial crescent; i.e. left or right side edge, depending on your season. Check out the design here: Alternative 3D Analemma for the Schmoyer Sundial Derivative by 3DMason | Download free STL model | Printables.com
The construction of this sundial is relatively simple, making use of M4 hardware. A list of assembly material is provided below, along with where it's used. All parts can be easily disassembled and reassembled to facilitate transportation.
All HW is Stainless Steel Button Head Hex Socket Head Cap Screws and Nuts, unless specified otherwise.
| Qty | Description | Where Used |
|---|---|---|
| 2 | 3 dia. x75mm rod | Holds the top & bottom of gnomon to the latitude scale crescent |
| 2 | M4x20mm screw | Used with bracket to hold top of time scale crescent to latitude scale crescent with nuts |
| 2 | M4 nuts | Used with above |
| 2 | M4x12mm screw | Used with bracket to hold edge of time scale crescent to latitude scale crescent. Screws to side of time scale crescent. |
| 4 | 3mm collar | Used to secure top & bottom of gnomon to 3mm rods |
| 3 | M4x20mm screw | For attaching pedestal to latitude scale crescent |
| 3 | M4 nuts | Used with above |
| 2 | M4x16mm screw | For attaching pedestal to base mount. |
| 3 | M4x30mm screw | For base leveling. Screws in at ends of base |
| 6 | M4 nuts | Locks base levelling screws (top and bottom) once level. |
Alternatives: Smart phone with: 1) Compass or GPS app, 2) level app.
See attached file section & look for Sunquest Equatorial Sundial - Assembly Instructions.
Before using, make sure that:
From Schmoyer Original User's Manual: "time is shown not by a shadow, but by a band of sunlight between two shadows cast by the gnomon on the time scale. The gnomon is turned by hand on its axis (from the top or bottom knob) to sharply define, broaden, or narrow the band of sunlight. The center band at the corner of both right-angled halves; i.e. on the gnomon axis, is an indication of the local sun time without correction. However, in reading the sundial in either the winter-spring face (from December 21 to June 20), or the summer-fall face (from June 21 to December 20 ), the surfaces are turned toward the sun, and gradually brought to a position at right angles to the direction of the sun's rays. In this situation two things happen:
The portion of the curved slot passing the sun's rays that meet the time scale changes from day to day and depends upon the declination of the sun. In summer the sun is high in the sky and shines through the upper, or north end part of the slot. The reverse is true in the winter when the sun selects an appropriate portion of the lower end of the gnomon slot, and offsets the necessary number of minutes on the time scale by casting the band of light projected by the analemma curve carved out of the gnomon plate."
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References:
License:
Creative Commons — Attribution — Noncommercial — Share Alike
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