Hi Frank and Roger.
I thought I'd respond to both of you letters since they are related... (Refer again to Time Zone Map: http://www.travel.com.hk/region/timezone.htm ) You're right Frank about "westward creep" of many of the time zones. Most of our time zones in the US and Canada extend more to the west of their Prime Meridians than to the east. So as far as land area goes, there generally is more land area west of the Prime Meridians- (I don't know if this extra land to the west also has more population in each zone since our population densities tend to thin out as you go west.) Looking at the map, check out your "westward creep" in Europe! The UK and Portugal are correctly colored yellow in the 0 degree zone, but the rest of Europe is all green- even countries that are west of your zone border like France, Belgium Holland and Spain. Look at the map of Canada, Roger. Your Eastern Time zone, in theory, should span from 67.5 deg W to 82.5 deg W. But it actually spans from about 62 deg W to 90 deg W! A definite westward creep over a 28 degree span. Your Mountain Time zone is even worse. Its Prime Meridian is at 105 deg W, but it spans from 102 way over to 137- That's a 35 degree span that's not even centered on the Prime Meridian! Strangely, the Prime Meridian is at the far Eastern edge of the Zone! All this Time Zone craziness is because local governments drew the time zone boundries. They tried to not isolate communities, states and provinces. They didn't want time zone boundries to slice through populated areas. They often would zig zag them around cities and states. (The Constitution does not stipulate time zones as it was written before time zones were invented.) But as cities grow, their old time zone boundries often no longer go around communites, but through them. If it gets really bad, they have to re-draw the boundries. I don't think this is done very often though because it just leads to more confusion. If your sundial is located far from its Prime Meridian in one of these crazy Time Zones, and you want it to give a time reading that is close to watch time, then designing it with built-in longitude correction is a must. If you forget about Daylight Saving periods, at worst, a longitude corrected dial will only be about 16 minutes off (because of the Equation of Time). On the average, it is only off by about seven minutes- good enough to keep most appointments! I know that I can glance at one of my sundials from a distance, and without using an EOT graph, that it is giving me a time that is very close to watch time. As Roger pointed out, a Solar Time dial doesn't even come close. For public wall dials that can be seen from a great distance, the person reading the dial might be a half mile away from it- too far to read a little EOT plaque. Doesn't it make sense to use a longitude corrected dial for public wall dials since the EOT graph is not availble to the far away users? John Carmichael John -----Original Message----- From: Frank King [mailto:[email protected]] Sent: Monday, February 14, 2011 3:44 AM To: John Carmichael Cc: [email protected]; [email protected] Subject: Re: part 2 of longitude correction Dear John, Your inspiring message about longitude correction prompts more thoughts from me. You say: > ... most of our [US] Time Zones have wiggly > irregular boundaries that sometimes span > distances far greater than 15 degrees. Everyone necessarily lives within 7.5 degrees of a multiple of 15 degrees but, as you correctly imply, time zone boundaries don't follow lines of longitude. You can live far more than 7.5 degrees from the multiple of 15 that goes with your clock time. Here I have a conjecture that applies specifically to the U.S. and, maybe, U.S. readers can tell me that I am wrong: A greater proportion of the population of the U.S. lives to the WEST of the multiple of 15 degrees that governs their clock time than lives to the EAST of that meridian. This is certainly true in the U.K. because only a tiny proportion of the British land mass is to the east of 0 degrees longitude. I just happen to live in that small bit. The conjecture is certainly true in summer when Daylight Saving Time shifts the relevant meridian 15 degrees further east but, I assert, it is true in winter too. Am I right? My conjecture is part of a bigger hypothesis that "time zones creep westwards". I assume that the wiggles are not hard-wired into the U.S. Constitution? My guess is that, every so often, a town close to a time-zone border asks to go to the other side. Is this right? If so, what is the procedure? By my hypothesis, towns on the west of a border more often ask for the border to be moved to their western side than towns on the east of a border ask for the border to be moved to their eastern side. There are villains in the U.K. who want the country to be in the Central European Time Zone. If this happened, it would be a spectacular example of a Time-Zone Creeping Westwards. All the best Frank
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