Tuesday, October 13, 2009

125 Years of Greenwich Longitude

The Prime Meridian at Greenwich Observatory (wikipedia)
We are used today to give the coordinates of a place on Earth using latitude and longitude, indicating longitude in degrees east or west, respectively, of the Greenwich Prime Meridian.

Thus, for example, the small amateur observatory Sternwarte Peterberg near the place where I did grow up is located exactly 7 degrees east of Greenwich.

However, looking up the location on historical maps, I don't find this longitude. Actually, the French engineers who around 1800 drew the first detailed topographic maps of the region did measure longitude with respect to the Paris Observatory. Their Prussian successors used the El Heirro Meridian, which goes back to Ptolemy in the 2nd century, and later switched to coordinates centered at Berlin.

Actually, in the second half of the 19th century, more than a dozen "Prime Meridians" were in use, creating increasing confusion for transport, trade, and communication around the globe.



Thus, in October 1884, delegates from 25 nations met in Washington, DC, at a conference to determine a prime meridian, which should be used as a universal reference for measuring longitude, and for a universal time. 125 years ago, on October 13, 1884, the "International Meridian Conference held at Washington for the purpose of fixing a Prime Meridian and a Universal Day" resolved
"That a meridian proper, to be employed as a common zero in the reckoning of longitude and the regulation of time throughout the world, should be a great circle passing through the poles and the centre of the transit instrument at the Observatory of Greenwich."
and
"That the Conference proposes to the Governments here represented the adoption of the meridian passing through the transit instrument at the Observatory of Greenwich as the initial meridian for longitude."

There was one negative vote, and the delegations from Brazil and France abstained from voting. The French delegation led by astronomer Pierre Jules Janssen, the discoverer of helium, had pleaded for keeping the El Heirro Meridian, but it seems that long tables of data, from tonnages of ships to sales figures of nautical charts and almanachs, all using Greenwich as their reference point, convinced most delegates to officially adopt the de-facto standard.

In 1911, also the French switched to Greenwich longitude and Greenwich time.




The complete PROTOCOLS OF THE PROCEEDINGS of the International Meridian Conference are available via the Project Gutenberg. The vote on the adoption of Greenwich meridian is reported on page 99.


10 comments:

Arun said...

My question is - who is going to set the galactic prime meridian? :)

Bee said...

The galactic prime meridian goes directly through this blog. You notice from the occasional alien commenter ;-)

Phil Warnell said...

Hi Stefan,

Thanks for reminding of the day it was decided where the earth should be considered to both begin and end. However, the reason for selecting the location stems back to more celestial concerns, beginning with the first occupant of what you call the Greenwich Observatory, which is more popularly known for him and thus referred to as Flamsteed House. Of course the main interest at the time was in having his charting of the heavens improve the accuracy of navigation; not among the stars mind you, yet upon the seas. Thus I find that despite the objection you noted by some, this to be chosen as ground zero so to speak.

The other thing I’ve come to admire about Flamsteed, is although he may have not been a match for Newton’s genius, he certainly proved to be more than one for his will. This serves for me to indicate that good science is not only reliant upon quickness of mind, but also on the strength of it as well.

Best,

Phil

Phil Warnell said...

Hi Arun & Bee,

I’m not certain about the location of the galactic prime meridian, yet I’d thought Kate Land and Joao Magueijo had suggested that the Axis of Evil might be taken as being the Universal one:-)

Best,

Phil

Bee said...

That must be why the Greenwich meridian goes though Iraq?

Phil Warnell said...

Hi Bee,

You mean to suggest that old George might have applied some level of reason in his decision making? Now the thought of that has me to become totally disoriented :-)

Best,

Phil

Bee said...

Otoh, as far as the French are concerned, the axis of evil probably goes through the UK, so maybe you have a point there ;-)

Phil Warnell said...

Hi Bee,

That’s the interesting thing about the French. That is despite the success of the Normand invasion, with having their kin come to run the place they still often consider the English as being both rivals and adversaries. I thus at times have found them even harder to fathom then old George as to their reasoning :-)

Best,

Phil

Uncle Al said...

The Milky Way is a barred galaxy. Run the Prime Meridian through the axis of a bar in the plane.

Kay zum Felde said...

Hi Stefan,


it is interestingly to notice that the velocity of light is only a constant of nature, since of the fact that the day is measured in meridians from noon to noon (Misner, Thorne, Wheeler).

Best Kay