My Unnatural Fixation with the American Meridian

On December 2, 2010 · 3 Comments

I’ll go ahead and crank up the old cliché generator and you can select the one you think would be most appropriate to the current situation: I’m like a dog with a bone; I’m pulling a thread from the sweater; I’m beating a dead horse, or all of the above.

The American Meridian continues to bedevil me. We’re trying to organize an American Meridian Gathering of Circulars.[1] Right now I’m planning to wait until after the holidays both because its a busy time of the year and because that will provide Catholicgauze of Geographic Travels an opportunity to participate. He is about to leave on a trip to Afghanistan.

I think a number of readers also had similar nagging feelings about the meridian. We all recognized the problem occurs because the American Meridian shifted a small amount over time. It doesn’t make much of a difference when viewed from a distance.

View American Meridian Line – in a larger map

Come in closer, however, and the variation become readily apparent. I’ve drawn three possibilities for the American Meridian and colored the distance between the extremes. That creates a fuzzy area and a level of doubt. I have to wonder if anything falling within the shaded box might be considered the meridian because of those shifts that took place over time, at least theoretically.

View American Meridian Line – in a larger map

The American Meridian started in 1850 as a longitudinal line running straight through the dome of the Old Naval Observatory. It moved three blocks east, from 24th Street to 21st Street in 1855 (current 77°2’48.0″). It shifted again by 1897, back to the west but still a little east of the 1850 line (current 77°3’2.3″). It changed a couple more times in the early 20th Century but those events happened after August 22, 1912 when the United States adopted the Greenwich meridian so I’ll not concern myself with them.

Wikipedia cites the American Ephemeris and Nautical Almanac and the Coast and Geodetic Survey for those longitudes. They are easy enough to drop into a Google Map and produce the images I’ve displayed on this page. Frankly I’m surprised at the amount of shifting that took place considering the importance of landmarks pegged to that line including several state boundaries. Granted most of that surveying happened during the period when the second line was in effect so maybe I shouldn’t be concerned, but a three block distance seems to be fairly significant.

Maybe we should consider the American Meridian "Line" as being three blocks wide? Maybe exact precision wouldn’t be appropriate for our purpose — Happy Hour socializing? This would place loyal-reader Craig’s suggested gathering spot, Mackey’s Public House directly atop the meridian.

View American Meridian Line – in a larger map

This also means that I work within a genuine geo-oddity. The land where my office building stands today began in the eastern hemisphere of the American Meridian, then shifted to the western hemisphere, then shifted back to the eastern hemisphere in the period between 1850 and 1912.

This pleases me immensely.

[1]Is that what we should call the regular readers of the Twelve Mile Circle? Anyone have a better suggestion?

On December 2, 2010 · 3 Comments

3 Responses to “My Unnatural Fixation with the American Meridian”

  1. “Is that what we should call the regular readers of the Twelve Mile Circle? Anyone have a better suggestion?”


  2. wangi says:

    NAD27 vs NAD83 vs … vs … ??

    • That provides even further complexity. The same Wikipedia article includes the statement: "When referred to later datums, this meridian has been variously specified as 77°3’6.119″W or 77°3’6.276″W (both presumably NAD 27). The first would be 77°3’5.037″W (NAD 83)." I think I’m getting a headache.

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