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Old 25-06-2012, 09:11   #1
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Longitude, Why East or West.

Does anyone know (or have a plausible theory) as to why we measure longitude as degrees east or west from the prime meridian.

Given the prime meridian is just an arbitrary line of longitude, why not measure longitude in degrees from that point staring at 0 and finishing back at that point 360 degrees later. Why differentiate between east and west going 180 degrees in either direction.

Surely there must be a reason!

Measuring latitude North or South seems self evident (at least to me ) but it is not self evident (again at least to me ) why longitude is so split into east and west. The only thing I can think of is that is makes the date line sort of easy to understand (I think )
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Old 25-06-2012, 09:16   #2
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Re: Longitude, Why East or West.

Ah! asking for logic to a political situation. Prime meridians were historically set through the capital city of what country was making the map.

I would "wag" it that the "east/west" was a committee compromise since it might not have been possible to designate longitude as "clockwise" or counter-clockwise" around the globe. After all, about half the world's people read left to right and the other half read right to left . . .
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Old 25-06-2012, 09:25   #3
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Re: Longitude, Why East or West.

the aussies have come up with a novel solution,and have placed australia at the top of the world on their new chart..............
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Old 25-06-2012, 09:28   #4
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Re: Longitude, Why East or West.

Maybe a cultural heritage from Tordesillas Treaty:

see: http://en.wikipedia.org/wiki/Treaty_of_Tordesillas
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Old 25-06-2012, 09:29   #5
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Re: Longitude, Why East or West.

Yes I get the political aspects to each choosing their own PM but considering that navigational matters were of very importance which occupied the minds of serious mathematicians and astronomers for centuries, it does seem that there "must" be a reason beyond political expediency - then again, perhaps not .

We are all political animals at heart!
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Old 25-06-2012, 09:31   #6
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Re: Longitude, Why East or West.

Quote:
Originally Posted by atoll View Post
the aussies have come up with a novel solution,and have placed australia at the top of the world on their new chart..............
The new north is south
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Old 25-06-2012, 09:59   #7
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Re: Longitude, Why East or West.

I suspect the answer is truly political. No matter how you measure longitude you will end up with a date/time discontinuity somewhere. Much better for the Brits and Europeans in general to have that discontinuity in the middle of the Pacific Ocean rather than in Greenwich.

John
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Old 25-06-2012, 10:05   #8
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Re: Longitude, Why East or West.

trigonometry,or calculating 3 sides of a triangle = 180 degrees
as from a position on earth the azimuth of the observed position can only be 180 degrees.

or to simplify Lha=Gha (of celestial body) minus-longitude (of observer)
which is calculated using 360 degrees silly
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Old 25-06-2012, 10:11   #9
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Re: Longitude, Why East or West.

As one is either north or south of the equator (zero degrees) -- one is also either east or west of the prime meridian (zero degrees). This makes for a symmetrical geographical reference.

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Old 25-06-2012, 10:14   #10
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Re: Longitude, Why East or West.

Jeees, have you got nothing better to do on a Sunday night?
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Old 25-06-2012, 10:25   #11
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Re: Longitude, Why East or West.

As the Meridian '0' degrees passes from the North pole to the South pole through Greenwich, the Western hemishere is obviously to the West of this line, and Eastern hemishere is to the East of this line. Mercator was the first to transfer the globe onto flat sheet of paper for navigation purposes and the Mercator projection, is still used on maps and charts.
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Old 26-06-2012, 05:42   #12
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Re: Longitude, Why East or West.

Thank you all for your replies, they are all believable to some extent!

However I like the two below the best


Quote:
Originally Posted by atoll View Post
trigonometry,or calculating 3 sides of a triangle = 180 degrees
as from a position on earth the azimuth of the observed position can only be 180 degrees.

or to simplify Lha=Gha (of celestial body) minus-longitude (of observer)
which is calculated using 360 degrees silly
Quote:
Originally Posted by Irish rambler View Post
As the Meridian '0' degrees passes from the North pole to the South pole through Greenwich, the Western hemishere is obviously to the West of this line, and Eastern hemishere is to the East of this line. Mercator was the first to transfer the globe onto flat sheet of paper for navigation purposes and the Mercator projection, is still used on maps and charts.
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Old 26-06-2012, 07:05   #13
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Re: Longitude, Why East or West.

Quote:
Originally Posted by Wotname View Post
Thank you all for your replies, they are all believable to some extent!

However I like the two below the best
longitude east or west is only a form of notation,or map reference,the calculation of longitude is calculated using 360 degrees of arc with greenwich at 0,and 360.

might have been a better answer!

the mathematics is just simpler when broken up into 90 degree segments.
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Old 26-06-2012, 07:13   #14
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Re: Longitude, Why East or West.

Quote:
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Surely there must be a reason!
Because 360 doesn't fit in 8 bits!
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Old 26-06-2012, 07:27   #15
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Re: Longitude, Why East or West.

Quite simply, Greenwich is the centre of the world. Or at least was, when these things were being established. At the end of the day, you either sailed East from Greenwich or left from Greenwich.
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