I don't have the data to hand, but from memory it's about 78 minutes and 150 metres or so at the surface (or the surface of SW England anyhow) - basically the earth wobbles!
To measure it, take a good INS, and a GPS system tied to it, then feed the position outputs from both into a computer. When you've data for 4 hours (more the better), plug the position data from both into a spreadsheet (or any other analysis package) and in a third column / data set calculate the linear distance between the two position reports. You should get a nice neat sine-wave of distance against time with a 78 minute period.
I did do this once as part of a student exercise at ETPS (comparing INS and GPS position reports on the school's BAC 1-11) but damned if I can find the graph I'm afraid, otherwise I'd post it.
Another way to do it would be with only the INS system, strap it down, and keep comparing position by distande from the first position report - should give you the same result.
Didn't somebody once use the frequency of the Schuler cycle to calculate the mass of the earth?
G
Last edited by Genghis the Engineer; 15th Feb 2004 at 08:08.