Introduction: Scarab 4 Season Sundial
Enjoying the ride? You know, the one with the 13 billion trillion ton spinning rock, circling an even larger ball of boiling nuclear fusion, at no less than 67,000 mph. Now that's a tilt-a-whirl. Here's a device that will give you a little reminder.
The shadow cast by the small brass pin (gnomon) tells the annual winter and summer solstice, and the fall or spring equinox. The seasons are determined by the apparent changing height or altitude of the sun above the horizon, high in summer, low in winter. The central vertical line serves as a solar noon mark, the sun at it's zenith or highest point.
No hour lines on this sundial, we're talking strictly space time.
The sun scarab is an ancient Egyptian symbol of renewal and rebirth, concepts central to that culture.
3/16" x 4 1/2" clear acrylic, length to suite.
1/8" matt orange acrylic (or similar sheet vinyl).
1/16" diameter brass pin.
3/4" x 1/2" x 4 1/2" hardwood for base.
Translucent matt "etched glass" sheet vinyl.
Your favorite vector graphics or CAD software program.
Step 2: Scale the Dial to Your Latitude.
www.shadowspro.com (free) will give you a very nice graphic of a vertical sundial facing south for your latitude. My latitude of 42 degrees north is represented above. You only need the location of the gnomon, gnomon length (A to B), and the upper, central, and lower lines that define the imposed cross size (in red) for your latitude (see above).
Scale the cross to the appropriate size (using the shadowspro software option) and position on the scarab graphic (PDF below) using a vector graphics or CAD program. Note: use the gnomon position already defined on the scarab graphic. Those living in latitudes closer to the equator may find the lower section of the cross that determines the summer solstice very long.
Prepare the clear acrylic sheet by cutting to size and polishing the edges with successively finer grades of wet sandpaper. The scarab PDF graphic is scaled to a 4 1/2" total acrylic width, but could be altered to suite your needs.
Once the file is set up, cut the transparent vinyl on a plotter, weed out the appropriate areas, and apply the vinyl. (tip: use the wet vinyl method for ease of application). An alternative would be using a laser engraver to etch the surface of the acrylic.
I used a CNC mill to accurately cut and inset the orange acrylic disc. An alternative would be to use colored transparent vinyl.
Step 3: Assemble
The 1/16" brass pin is carefully cut to the required length (A to B) plus the acrylic thickness. A 1/16" hole is drilled (drill press is best) in the appropriate spot and the pin inserted on the vinyl side of the acrylic.
The base is a 3/4" x 1 1/2" x 4 1/2" piece of hardwood. I used a table saw to cut a 3/16" x 3/8" deep slot to hold the acrylic. For safety I cut the slot in a longer piece, then cut to length. The base was then stained black.
Step 4: Setup and Use
The dial must be positioned so the gnomon/vinyl side faces due south (north in the southern hemisphere). The easiest way to do this is to determine a date and time for exact solar noon for you specific location, which can be found on line at "NOAA Solar Calculator". At the time and date specified for your location, position the dial so the gnomon's shadow lands exactly in the middle of the central vertical noon line. Mark the surface where the base edge sits with a piece of tape or other method for future reference. The surface must be level.
Observing the shadow's movement throughout the year as it moves from winter to summer and back will give witness to the great ride. Search "earth sun geometry" for more information on how the seasons are determined by earth sun interaction.
"I'm gonna kiss that pretty girl, on the tilt-a-whirl". (The late great John Prine, "When I Get To Heaven".)
Participated in the