Hi John and all, Thanks for the perspective and the time zone map. You are correct that we have no real tradition for sundials. Most people here expect sundial to tell time as they know it. They don't realize that sundials tell the true time when high noon when the sun is above your meridian is 12:00, halfway between sunrise and sunset.
A good test is whether an uncorrected sundial will ever show clock time at your location. It will twice a year within a band 4.1° west in the fall or 3.7° east of the time meridian, 15° intervals of longitude around the world. That is a band of about half a 15° time zone. Note many time zones are not centered on the mod 15° meridian. Draw the lines on a map like the one in the link. I made a little clear plastic template to slide over the map. Uncorrected sundials will never show clock time during daylight savings, the spring and summer, so the smaller peaks on the EQT are never in the correct zone. Most of the UK fits the criteria, as does most of Germany, Netherlands, Austria, Italy, etc. The criteria always fails in daylight savings times, always fails in France, Spain etc, often in most of China and Russia and many other parts of the world. It fails for you John as you are almost 6° west of the 105° meridian. It works for me at 123.4° west of about 15 Oct and 25 Nov. Test your location. I am sure there are exceptions to these general statements. Regards, Roger Bailey Walking Shadow Designs From: John Carmichael Sent: Sunday, February 13, 2011 9:28 AM To: [email protected] Subject: RE: part 2 of longitude correction My friend, Jim Tallman and I have had many discussions about longitude corrected dials. I know that many of the Western European dialists don't like longitude corrected dials- especially the British dialists. I can see why they feel this way. Their three biggest arguments against longitude corrected dials are these: 1) They aren't traditional, 2) They aren't symmetrical, 3) They are so close to their Prime Meridian that the longitude correction is quite small and almost insignificant. But there are equally good arguments for longitude corrected dials! In The United States, and many other places, the sundial may be located far away from the Prime Meridian at the edge of a Time Zone. In a perfect World, a Time Zone would only span 15 degrees. But most of our Time Zones have wiggly irregular boundries that sometimes span distances far greater than 15 degrees. Russia is an extreme example of this! There are parts of Russia that are missing entire zones! Then there's China. The entire country only has one Time Zone! See: http://www.travel.com.hk/region/timezone.htm For places like these, a well-built traditional Solar Time sundial will give a time reading that can be more than an hour off of Watch Time (Standard Mean Time). A casual non-dialist would say that these sundials don't work, especially if there is no Equation of Time graph available with built-in longitude correction! Correcting a dial for longitude solves this problem. For this reason, I think longitude corrected dials are more user-friendly. This is why Jim and I routinely make our dials with longitude correction. That's my two cents worth. John Carmichael
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