Thanks for the graph, Luke. If I take +/- 20 sec as the accuracy of a very good sundial, then I see that I have to start correcting for refraction around 10 deg altitude, i.e., the first hour after sunrise and the last hour before sunset. Since Pete Swanstrom's earliest observation is at 7:10 am on May 6, when the sun in Boise is 16.5 deg above the horizon, it is not surprising that he saw no refraction effect. If you don't feel like a stroll in the park at 5:30 am, Pete, how about taking a series of measurements in the last hour before sunset, between 7:30 and 8:30 pm?
Art Carlson
