created by Carl Sabanski
Hours Before Sunset Sundial Kit
This universal hours before sunset sundial is based on a design developed by Mac Oglesby.
Figure 1 shows the Kit that you will use to make your own universal hours before sunset (HB4SS) sundial.
Figure 1: Hours Before Sunset Sundial Kit (CAD)
is designed so that you can build one for the
Northern or Southern Hemisphere. All you need are scissors, styrofoam, glue and
a wood dowel. The dial is a lot of fun to
make and would be a great science project. If you would like to download a
PDF file of the "Hours Before Sunset Sundial Kit" just open the door.
The sundial must be assemble for it to function correctly. Figure 2 shows a photo of the completed sundial. The hour line plate rotates about fixed dowel at the centre. The dowel is fixed to a circular plate behind the hour line plate. During assembly the North arrow on the hour line plate must be aligned with a similar arrow on the back of the fixed circular plate. When the dowel is glued into the fixed circular plate the pointer must be positioned on the "0" line.
When you have completed the sundial all you have to do is set up and it will tell you just how much time you have before sunset. 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. The dowel that holds the metal pointer will be aligned with the celestial pole.The sundial does not need to have the Equation of Time or longitude taken into consideration.
Figure 2: Universal Hours Before Sunset Sundial
The sundial in Figure 2 is set for a latitude of 50º N. The next step is to position the hour plane plate, which must be rotated to a horizontal position. Use a string level or other small level to do this. The sundial is now ready to use. The top of the cylinder must be parallel to the hour plane plate and the vertical line that was transferred to the outside must be aligned with arrow on the hour plane plate.
To determine the number of hours left until sunset rotate the hour line plate until all the sun's rays exit the top of the cylinder. At this point the top of the cylinder lies in the present hour plane and the pointer indicates the number of hours before sunset. The cylinder also has a small hole or aperture and a line drawn on the inside. When the light beam from the hole is positioned on the line inside this too indicates the hour plane plate has been rotated to the correct position. This feature is useful when light levels are low and it is difficult to determine when the sun's rays exit the top of the cylinder.
The following are additional photos of the sundial.
Universal Hours Before Sunset Sundial - Rear View
(The aperture, stationary circular plate and the latitude scale can be seen.)
Universal Hours Before Sunset Sundial - 3 Hours Before Sunset