A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: no leap second coming in December
From: Richard Irvine
Date: 2004 Jul 28, 11:03 +0200
From: Richard Irvine
Date: 2004 Jul 28, 11:03 +0200
Intersting posting ... I think the history of science is full of cases in which the detection of phenomena of which we were previously unaware follows someone paying attention to what at first seems a minor detail. -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM] On Behalf Of George Huxtable Sent: Wednesday, July 28, 2004 1:29 AM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Re: no leap second coming in December Thanks for information from Richard Langley and Andres Ruiz about this topic. Perhaps I can summarise the situation as follows- Right through most of the 20th century, up until 1994 or so, the difference between Ephemeris Time and Universal Time , or delta-T, increased each year by about 0.7 seconds. But over the last six years or so, this quantity has stopped increasing and at present remains roughly constant. This must be the result of the Earth's spin speed having increased, by about 1 part in 40 million, rather suddenly, within a very few years. I know that delta-T has fluctuated significantly in the past, but this time there seems to have been a rather sudden increase in spin speed, by quite a large amount. What could be the cause of this rather dramatic change? One part in 40 million may not seem a lot at first sight, but in view of the immense angular momentum of the Earth, some large torques must have been at work. I would like to muse about some possibilities, aware that it's somewhat off-topic for navigation, but asking for a bit of indulgence on that score. It can't possibly be due to tidal friction, which causes angular momentum to be transferred from the Earth to the Moon, can it? That is strictly a one-way process, which can only ever act to slow the Earth's rotation, and never to speed it up. Could the Earth have shrunk slightly, perhaps? That would speed up the spin, as it does for an ice-skater doing a pirouette, as she draws in her outstretched arms. If the Earth radius were to shrink by one part in eighty million, with all its inner layers shrinking in proportion, that would be enough to do the trick. That needs no more than 3 inches or so shrinkage in radius. I suspect geodesists would be able to detect such an unlikely event using modern technology. It couldn't possibly be due to interaction with the moving atmosphere, which doesn't carry nearly enough mass to have sufficient effect. If the oceans were to acquire a change in East-to-West drift right around the Earth, including the Drake passage round the Horn, that would speed up the Earth's rotation, which is in the opposite direction. But to have sufficient effect, such a current drift would have to be sufficiently large that it would have been perceived already, according to my rough estimates. We keep getting told that the polar ice caps in Antarctica and Greenland are melting. However, this displacement of mass, from being locked in the ice caps near the Earth's axis, where it has little effect on the Earth's rotational inertia, to disperse around the oceans where its effect on inertia would be greater, could only slow the Earth's spin, not speed it up. The only other possibility that I'm aware of (and listed by Richard Langley) is a change in the circulating currents within the Earth's liquid interior. We know that these exist, and change, because these motions in the conductive liquid result in the ever-changing magnetic field pattern of the Earth. It seems most likely, to me, that there has been a significant increase over recent years, and a rather sudden one, in the component of overall swirl in the opposite direction to the rotation of the Earth. I wonder whether any such changes may be detectable in terms of a sudden effect on the Earth's magnetic field over recent years. It's just a thought. I admit to knowing little about geophysics, and hope that others, wiser about these matters, will correct any errors in my speculations. George. ================================================================ contact George Huxtable by email at email@example.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================ ____ This message and any files transmitted with it are legally privileged and intended for the sole use of the individual(s) or entity to whom they are addressed. If you are not the intended recipient, please notify the sender by reply and delete the message and any attachments from your system. Any unauthorised use or disclosure of the content of this message is strictly prohibited and may be unlawful. Nothing in this e-mail message amounts to a contractual or legal commitment on the part of EUROCONTROL unless it is confirmed by appropriately signed hard copy. Any views expressed in this message are those of the sender.