Solar Telescope Demonstration Sundial Marking Technique
June 19, 20 & 21 2002

From June 19 to Jun 21, a team of 5 volunteers helped me to mark the time points and seasonal markers of the demonstration sundial using the shadow of the solar telescope's angled polar axis structure (the light tube). We located the position of the marks using the very precise "Time Method" which employed the fuzzy edge (the penumbra) of the shadow, an image projection screen, a precision radio clock and the Equation of Time Conversion. We marked the points on the chip & seal asphalt surface with 2 inch flat-head roofing nails with bright orange 1" washers. This is the procedure we used:

Above: NASS members John Carmichael and Bob Hough marking the time points of the McMath-Pierce Telescope Demonstration Sundial. Bob Hough holds the shadow sharpener.

After checking into the cozy cabins provided by Kitt Peak, three of us (John Carmichael, Bob Hough and Cristina McVie) arrived on site at 4:00pm and we laid out the west, north and east borders of the rectangular shaped sundial using bright orange surveyor's string. We wanted all three border timelines to be in place so that we could begin practice markings at sunrise the next day. Using the south corner of the Heliostat Tower as our reference point and the border locations desired by Kitt Peak, we determined the position of the perimeter time markings. (This rectangular dial face has markings on the west, north and east sides and we will refer to them that way). We put nails a little beyond the corners and at the sunrise and sunset points on the perimeter timelines then we stretched surveyor's string between the nails and swept the excess pea gravel away with a push broom from underneath the string to expose the smoother black asphalt below. A smooth surface would allow the head nails to be driven in completely. The Delta Cad original sundial drawing I did for the proposal served as a useful guide, but we had to relocate the east timeline several feet to the west because of chain link fence that was in the way. We noted the shadow at sunset so that we knew how long to make the east timeline.

June 20

Jun 20 was our practice day when we refined our techniques and did some experiments. Having this extra day proved to be a very wise decision! We were on site at 5:00am before our estimated sunrise at 5:22:47am. We placed all our equipment on the south end of the west timeline string where we estimated the sunrise shadow would be so that we would be ready when the sun rose. There was almost no horizon pollution to the northeast and using eclipse glasses, we observed the ½ solar disk rise above the distant mountains at 5:21:10am. The telescope's shadow appeared and we marked this point as the summer solstice sunrise time point. Then began the grueling schedule of marking time points every 5 minutes and all the other seasonal markers, style shift marks, and the High Noon mark. We worked in alternating shifts that we all agreed upon until sunset at 7:24pm. (Theoretical sunset time was 7:31, but a little horizon pollution made it happen at 7:24pm) There were 182 time points, six seasonal points, two style change points and one high noon point for a total of 191 points. We only missed two points during the day which we later marked using guesstimation and a ruler.

We used a pre-calculated Sundial Time/Mountain Standard Time List provided by Bob Hough that equates sundial time to watch time for June 20 so that we would avoid math errors by doing The Equation of Time corrections in our heads. For maximum precision, Bob had calculated the exact Equation of Time values for each and every point on the sundial! For easy reference, we had this printed time conversion chart and a drawing of the sundial face attached to a clipboard that we moved around with us. This list was indispensable.

To mark the timeline points, somebody had to watch the radio clock at all times. Another person held the 2 mm pinhole shadow sharpener at least 1 meter above the ground in the shadow's penumbra region so that the 1/2 solar disk image was centered on the string. This was somewhat difficult and required some practice, especially since we were battling 50 mile per hour winds for most of the day and it was hard to hold the sharpener still. The winds were so strong that we had to weight all our equipment down with rocks!

Because the asphalt was dark and uneven and made the image difficult to see, we placed a 1/8 inch thick, 18 inch long and 3 inch wide strip of beige flat particle board underneath the orange string to serve as the pinhole image projection screen and we slid it along the line as the shadow's penumbra moved. The clock person gave us 1 minute warnings so that we could get ready, then, counting down the seconds, at the correct radio clock time indicated on the Sundial/Watch Time list, the image location was noted, the screen removed and the nail person drove a nail into the asphalt at that point next to the string. We nailed small flat metal waterproof numerals and letters (Like the little metal ones you see on mailboxes) on the Hour, High Noon, style changes and seasonal points; and we marked the 15, 30 and 45-minute points with paper tags. Underneath the nail heads we placed bright orange washers for greater visibility.

We had a major problem after 12:50pm. This point is at the northeast corner of the sundial face. Shadow velocity increases dramatically after 12:50 because of the changing geometry of the borderlines. It was moving so fast (about 2 cm/second) that the person holding the shadow sharpener couldn't keep up and we missed a couple of points. Knowing this would happen again the next day, we were prepared for it so we wouldn't make the same mistake again. We also noted some rocks that were in the way on our late afternoon points so we had to shift the entire east timeline 23 cms to the east.

After sunset we were completely exhausted and went to bed early!

June 21 (Summer Solstice)

With two new additional volunteers on site (Tom Maza and Mark Klingensmith), we repeated the marking procedures we perfected the day before. The extra help proved to be invaluable since there were constant distractions from visitors asking questions, and with extra people, we could take more rest and food breaks. Volunteer movie photographers Rich Richey (a docent tour guide at Kitt Peak) and Tom Maza filmed close-ups of the marking technique and a movie of the morning style shift. Unfortunately, we were unable to film a time-lapse movie because we didn't have enough time or the equipment to do it. But we also took still shots with a 35 mm camera.

In case these temporary markers are removed for some reason, and we need to reconstruct them in the future, after we marked the points, we placed a 100 ft. measuring tape along each time line and we wrote down the exact distance each point was from a corner point. With this information I can make a new Delta Cad drawing of the dial face as it actually is. And these points may help in the construction of a permanent sundial.

When finished, I looked at the dial face from a distance and saw that I couldn't read any marker points because they were so small. To read the markers, you had to be near them. It was immediately apparent that the sundial lacked a sculptural presence. So, we placed rocks next to each point. We placed Big rocks next to the hour and seasonal points, medium size rocks next to the ½ hour points, and little rocks on the 5 minute points. These crude markings helped immensely to visualize the sundial and allow the user to read it from a great distance.

At sunset, we marked the last point and toasted to celebrate the finished sundial.

The Future Hopefully, the demonstration sundial will create interest and funding for a much nicer permanent sundial in the near future and that our experiences will help other dialists who wish to use the Time Method to mark future monumental sundials. We hope to monitor the demonstration dial at different dates to check its accuracy.

Note on Precision:

If we did our marking correctly, the biggest factor affecting precision will be the straightness of the styles. I suppose this could be checked exactly by using a laser, but lacking one, all we could use was our eyes. By placing one eye at the base of a style, we could look straight up the edge of the styles. We did see very slight undulations in the styles, but we guesstimated that they were only between I and 3 inches, a very small amount if you consider the enormous size of the sundial. These could only affect the precision of the dial by a few seconds. Time will tell!