My OperaMystery (part of it at least) Solved
Tuesday, February 1, 2011 7:44:22 AM
In my last post I was wondering why my GPS appeared to be in error, while standing on the prime meridian. I had several theories, one was that the GPS constellation was a US military installation, and as such they have the right to "scramble" the signals creating an error in times of heighened security or threats. I thought this might be the case, but as I wandered something else came to mind. I found this placard
The prime meridian was used for land maps and star charts. At the obseracory a telescope was placed on the meridian, and it pointed straight up. Then astronomers recorded the precise time that certain stars crossed the meridian. If you know the time at the meridian, and the time that the same star is directly overhead at your location, you can determine your longitude. Charting the stars and creating star charts for the mariners was a full time business at the observatory. So, when a new larger telescope was installed a few feet east, the meridian moved with it. The close black doors are where Bradleys telescope looked at the stars. The open white door farther down are where the new telescope was positioned, and is now the prime meridian.
I thought this was the answer, until I realized that the error was in the other direction. I was still perplexed so I continued to wander, and then I found this gem.
I have not researched the reason for the third meridian, but this picture was taken from the US Military Prime Meridian, looking West to the other one.
My guess is that somewhere there was monument, at say 100 W (Where the Great Plains Begin - The Tragically Hip), which was used to calibrate the early GPS devices. Then they discovered the monument placement was in error, but it was easier to change the one over in Britian, than the one in the US, and besides the Brits has two different prime meridians anyhow ( and probably something about dumping the tea overboard) (My Historical facts may be a little inaccurate here). Or perhaps it was a land grab by a non US Nation. For example,My countries border is a very long line defined by the 49th Parallel. If you move that line 100m to the North, over 5000 kms, it amounts to a fair chunk of real estate. I am not aware of any North South borders defined by longitude, but then again my geography rates right up there with my world history.
I still cannot figure out how global warming and the rising sea level accounts for the height inaccuracy.
Cheers
Not Quite Out By A Mile Bryan
The prime meridian was used for land maps and star charts. At the obseracory a telescope was placed on the meridian, and it pointed straight up. Then astronomers recorded the precise time that certain stars crossed the meridian. If you know the time at the meridian, and the time that the same star is directly overhead at your location, you can determine your longitude. Charting the stars and creating star charts for the mariners was a full time business at the observatory. So, when a new larger telescope was installed a few feet east, the meridian moved with it. The close black doors are where Bradleys telescope looked at the stars. The open white door farther down are where the new telescope was positioned, and is now the prime meridian.
I thought this was the answer, until I realized that the error was in the other direction. I was still perplexed so I continued to wander, and then I found this gem.
I have not researched the reason for the third meridian, but this picture was taken from the US Military Prime Meridian, looking West to the other one.
My guess is that somewhere there was monument, at say 100 W (Where the Great Plains Begin - The Tragically Hip), which was used to calibrate the early GPS devices. Then they discovered the monument placement was in error, but it was easier to change the one over in Britian, than the one in the US, and besides the Brits has two different prime meridians anyhow ( and probably something about dumping the tea overboard) (My Historical facts may be a little inaccurate here). Or perhaps it was a land grab by a non US Nation. For example,My countries border is a very long line defined by the 49th Parallel. If you move that line 100m to the North, over 5000 kms, it amounts to a fair chunk of real estate. I am not aware of any North South borders defined by longitude, but then again my geography rates right up there with my world history.
I still cannot figure out how global warming and the rising sea level accounts for the height inaccuracy.
Cheers
Not Quite Out By A Mile Bryan
