Standard Time Equatorial Ring Sundial Kit

Analemmic Sundial: this term has sometimes been used to describe dials which have an analemmic shaped gnomon, or analemmas on the hour lines, enabling them to read mean time.

Equatorial Sundial: a dial in which the dial plate is parallel to the equatorial plane and the polar-pointing gnomon is perpendicular to it.

Heliochronometer: a precision sundial which incorporates some means to allow it to read civil (or mean) time.

Vernier: a small moveable scale for obtaining fractional parts of the subdivisions of a fixed scale. Invented by Pierre Vernier in 1631 (published Brussels, 1638). For circular scales, a Type A vernier has a central zero.

The equatorial sundial is a universal dial and can be used anywhere in the world. All you have to do is position it correctly and it will tell you the time. It is quite easy to make as the hour lines on the sundial are placed at intervals of 15° for every full hour. Because of  the equal hour intervals it is possible to correct the sundial for longitude and the Equation of Time (EoT)  just by rotating it. The longitude correction is constant but the EoT changes each day. The adjustment must be made every day for maximum accuracy. Once done the sundial will indicate standard or clock time. This sundial is also referred to as an analemmic sundial or heliochronometer.

Figure 1 shows the Kit that you will use to make your own standard time equatorial ring sundial. This sundial will work throughout the year.

The sundial is made using paper and styrofoam. Be careful when constructing this sundial to make sure the inside dimension of the ring shown on the right of Figure 1 is kept at 8 inches. The hour line ring is kept in place in its slot by maintaining a tight fit. This allows it to be rotated in either direction to correct for the Equation of Time and/or longitude. As the hour lines are drawn at 10 minute intervals a vernier scale is included to help adjust the correction to the nearest minute.

Figure 1: Standard Time Equatorial Ring Sundial Kit  (CAD)

The sundial is designed so that you can build one for the Northern or Southern Hemisphere.  If you would like to download a PDF file of the "Standard Time Equatorial Ring Sundial Kit" just open the door that works for you.

Northern Hemisphere	Southern Hemisphere

There are actually three versions of this sundial in one kit. The difference is in the gnomon. The gnomons are shown in Figure 2. The first and simplest gnomon is a straight rod. It can be easily made from a metal clothes hanger. When using this gnomon the hour line ring must be rotated to correct for both the Equation of Time and longitude. This gnomon requires adjustment every day. The other two gnomons are analemmic gnomons. They differ in how they project the analemma on to the hour line ring. One is solid and projects light through the analemma shaped cut out. The second is printed on a transparency and will project the analemma as a thin line. When using these gnomons the hour line ring is rotated to correct only for the longitude.

Figure 2: Standard Time Equatorial Ring Sundial Gnomons

The rod gnomon is in the centre of the photo. The analemmic gnomons are on the sides with the the transparent gnomon on the right. The two small rods on the left are used to secure the top and bottom of the analemmic gnomon in place and allow the gnomon to rotate. The date lines are spaced every 5 days as indicated on the gnomon.

To set up this sundial place it on a level surface and align it with you local meridian, i.e. the true north-south line. Rotate the sundial until the "Latitude Pointer" is aligned to the correct latitude. A vernier scale is used to set the angle of the sundial to the nearest 1/4º for a latitude scale spaced at intervals of 1º. To learn more about the vernier scale visit the "Standard Time Equatorial Sundial Kit" page. When using the rod gnomon read the time indicated by the centre of its shadow, When using the analemmic gnomon rotate it so it faces directly at the sun. Read the time at the centre line of the hour line scale. Use the dates to determine which side of the analemma to read from on a particular day.

Here's what the sundial will look like once you have finished making it.

Standard Time Equatorial Ring Sundial - Front View

(Shown with the rod gnomon so the hour line ring and vernier scale can be clearly seen.)

Standard Time Equatorial Ring Sundial - Side View

(The latitude scale can be seen in this photo.)

Standard Time Equatorial Ring Sundial - Analemmic Gnomon

Standard Time Equatorial Ring Sundial - Transparent Analemmic Gnomon

Happy Dialling!