Hello All: I've been enjoying the discussion on the delay of sunset due to refraction. Somewhere I heard that at mid latitudes this is about three minutes. Can anyone confirm this?
Here is the reason I ask. On the outer edge of my horiz. sundials I engrave little sunrises and sunsets which mark the time and direction of sunrise and sunset on the equinoxes and solstices. Not knowing how to calculate the placement of the engravings with math and formulas, I used a simpler (for me) technique. Before starting I already knew that the sun should set due west on the equinox. To find out where the sun rises and sets on the solstices I first obtained U S Naval Observatory printouts of the times of sunrises and sets and then plotted these times onto the sundial face. This automatically gives the directions. ( I use the average times over several years as the time of rise and sets vary by a couple of minutes each year). A problem arose, however, when I plotted the equinoxes. The direction of the rises and sets was a several degrees SOUTH of due east and due west! Could this be that in theory the sun sets due west on the equinox (as it would if the earth had no atmosphere) but in reality is sets slightly south of due west due to refraction, and would this explain the time delay? This has really bothered me, because I want my dials to be correct.(my dials are corrected for longitude and I corected the observatory times with the EOT) Please comment on this somebody! John Carmichael thanks
