Prime meridian and continental drift

Hiya.

Just finished reading “Longitude” by Dava Sobel and I wondered how do people keep the prime meridian exactly in place when the Earth’s plates are moving (even if pretty slowly)?

Do they just assume that Greenwich is stationary and the rest of the world moves slightly, or is the difference so small that no-one really cares for that much exactness?

Stupid question I know, but these things pop into my head from time to time…

Here’s a couple of phd types dicussing this very question:

heh…from your link:

I guess it wasn’t such a stupid question after all! :slight_smile:

Thanks pravnik. I wonder if anyone since has actually checked to see if there is an ofset from Greenwich, since that was posted in 1999.

I would be pretty surprised to find that anyone has measured the drift of Greenwich away from the prime meridian. It’s not technically difficult - one just has to place sensitive GPS (global positioning system) receivers in the appropriate locations in order to track plate motions at the level of fractions of centimeters per year. However, that sort of attention is usually reserved for actively deforming plate boundaries (like the San Andreas Fault, which IS monitored this way) where seismic hazards are a concern, and not relatively peaceful intraplate areas like merrye olde England. So if you’re really dying to know, I’d suggest renting some receivers and hiring a few starving seismology grad students to place and maintain the GPS stations for you. :slight_smile:

From History of the Prime Meridian:

Apparently, the prime meridian is part of a fixed, earth based coordinate system, so it’s not moved to account for continental drift. However, it’s been supplanted by other coordinate systems which do include corrections for plate movement.

I’d typed up a post based on Carl Calvert’s appendix note in the 1997 reprint of Derek Howse’s classic Greenwich Time and the Discovery of the Longitude (Oxford, 1980), put it to one side while the hamsters risked strokes and then find five minutes later that Squink has found a website with a variation on Calvert’s note. The odd think is that this has made me notice that in 1997 he had the International Reference Meridian 102.5 metres west of the Airy transit, while the website puts it the same distance east. Someone’s clearly had to correct a minus sign at some point.
For what it’s worth, the post concluded:

No such luck.