(That's a Monty Python reference, for those who are puzzled by the the subject line.) Harald Alvestrand wrote: > one of the amazing things I discovered some years ago when browsing the > website of the Institute for Earth Rotation (!) is that leap seconds can't > be predicted more than approximately 5 years in advance. > > it's a strange world. Spike Jones (live long and prosper, Spike :) wrote: > Not so strange. The rule that always holds is the conservation of > angular momentum. The uncertainty is in the moment of inertia of > the earth. Movements in the tectonic plates cause slight variations, > enough to throw off predictions of leap seconds. spike I read an article a couple years ago in Science that showed how even the daily cycle (used by many electric utilities around the world) of i) during high-demand (daylight) hours, supplement the 24-hour power sources (e.g. fossil-fuel-burning or nuclear power plants) by discharging water from a high-level to a lower-level reservoir; ii) at night, use some of the now-regained excess capacity on the electric grid to pump the water back up into the high reservoir causes (like the proverbial skater pulling her arms in and back out) a discernible variation in the Earth's rotation rate. I suppose excavating a large open-pit mine and piling the tailings up on higher ground would similarly cause a noticeable change. Sea levels rising due to global warming should cause a very noticeable change in the faster-rotation direction, if the ice that melted was originally at a significantly higher elevation than the resulting sea level. In fact, rotation-rate changes due to sea level change should be of a similar order of magnitude as those due to tectonics, but would occur on much shorter time scales. 'Tis fascinating stuff, albeit wildly off-topic... Cheers, -Ernst _________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
