Schmoyer Equatorial & Analemmatic Sundial Derivative

Introduction

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.

Change History

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: 

• a gnomon, or shadow-casting device; 
• an equatorial time-scale crescent; 
• a crescent supporting the gnomon and the time-scale crescent, called the latitude crescent; 
• a pedestal & base; 
• a daylight saving time stop and longitude setting and;
• a gnomon adjuster for the solstice periods. 

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

Main Features

• 5 minute reading resolution on the time-scale crescent;
• 1 degree adjustment resolution on the latitude crescent;
• Improved construction, using minimum number of parts and a simplified but reinforced latitude crescent;
• Computes corrections to the true, or apparent solar time by utilizing a visual-mechanical computer, otherwise known as an analemma, which is incorporated within the gnomon;
• Note that this version of sundial does not make correction for Local Mean Time to Standard Local Time via meridian dial offset adjustments.  Additionally, it cannot be adjusted to display daylight savings time directly.  These features may be added in future revisions;
• 4 base options are available; 3 with integrated magnetic compass and levels, and 1 without.  For compass/level options, refer to these printable links:
  • Tri-leg:  Improved Heliochronometer Sundial Base Design with Integrated Bubble Levels and Magnetic Compass by yba2cuo3 | Download free STL model | Printables.com
  • Leveling base & tripod head:  Heliochronometer Sundial Mount for Head Leveling Base or Tripod Ball by yba2cuo3 | Download free STL model | Printables.com
• Assembly measures 200x200x200mm (W x L x H).

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

Print Settings

• Printer brand:  Prusa
• Model:  i3 MK4S
• Supports:  Yes
• Resolution:  0.15mm Structural
• Infill:  20%
• Brim: No
• Filament brand:  Doesn't matter
• Filament material:  ABS
• Filament color:  Doesn't matter
• Special Notes:  
  • Print in an enclosure for best results. 
  • Use a darker color filament at a specific layer height to highlight the text if you have a single extruder. 

Construction

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.

List of Required Assembly Hardware

All HW is Stainless Steel Button Head Hex Socket Head Cap Screws and Nuts, unless specified otherwise.

Post Processing Tools

1. Deburring tool for removing excess plastic from printed parts
2. Hand Drill or Drill Press (optional)
3. 3.3mm or 1/8" drill bit for enlarging holes for M4 tap (optional)
4. M4 tap for making threads (optional)

For Sundial Alignment 

1. Magnetic Compass
2. Circular Bubble Level

Alternatives:   Smart phone with:  1) Compass or GPS app, 2) level app.

How to Assemble

See attached file section & look for Sunquest Equatorial Sundial - Assembly Instructions.

How to Use

Before using, make sure that:

1. your sundial is perfectly level;
2. your latitude is set on the latitude crescent;
3. the gnomon axis is properly pointing to true celestial north.  See refences below for alignment procedures. 

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:

1. Turning beyond a right-angle shuts out the direct sunlight entirely, but just short of a position squarely facing the sun, the band can be as fine as you care to see and use to interpolate between the 5-minute graduations;
2. The band of sunlight is shifted from the gnomon axis, which was showing local mean or sun time, to fall earlier or later on the time scale by an interval necessary to show local mean time instead.

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."

If you think this is a cool design, don't forget to hit the like button. I hope you enjoy building this design & thanks for your support!

References:  

1. Richard Kellogg - NASS: 3D-Printed Schmoyer Sundial
2. Scientific American - Amateur Scientist - 1959 (see file section)
3. Schmoyer Sundial User's Manual (see file section)
4. Heliochronometer - World's Most Accurate Sundial by yba2cuo3 | Download free STL model | Printables.com
5. Gard Heliochronometer Sundial Derivative by yba2cuo3 | Download free STL model | Printables.com
6. Sundials - Their Construction & Use, R. Newton Mayall & Margaret Mayall, Dover Publications Inc., 1994
7. The Equation of Time:  The Equation of Time