Hi Ken, Thanks for calling to check on the layout of the zodiac on the Elliston Park analemmatic sundial. I understand your concern when you put the precast date blocks in place and checked the time, the dial fast by almost one hour and 20 minutes. I am glad you called before pouring the concrete and casting things in stone.
This discrepancy between sun and clock time is as expected. The layout is correct. This is a bad time of the year for setting sundials as we just changed from daylight sayings to standard time and the equation of time correction if greatest at this time of year, 16 minutes 28 seconds sun fast. The total correction today should be 1:16:28, sundial fast. Your reading confirmed that the axes, N/S and E/W, are correctly oriented to the sun, the zodiac table is correctly aligned for the date and hour posts are in the right place, offset by 36 minutes to account for longitude. The dial was designed for summer use and the brass numbers in the hour posts indicate daylight savings time. Most use of the dial will be between April to October so the daylight sayings markings are appropriate. The equation of time is the difference between average clock time and variable solar time. These variations are due to the tilt of the earths axis and the elliptical orbit of the earth around the sun. No correction is required in mid March, mid June end of August and late December. The corrections are moderate in the spring and summer when most people will see the dial, 4 minutes fast in May, 6 minutes slow in July. The worst case happens to be today with a maximum correction of 16:28 fast. In February the dial is as much as 14 minutes slow. I did not design this correction into the dial. It is difficult to do and adds an unwarranted level of complexity. I hope the concrete pour and finishing went well so the dial can be completed before the weather really closes in on us. Roger Bailey Walking Shadow Designs N 51 W 115
