Earth's Gravitational Field Is Getting Flatter

RJG2 writes "MSNBC has an article stating that Earth's gravitational field has changed, becoming stronger towards the equator, thus becoming flatter. The cause has yet to be determined, but it is assumed changes in ocean levels are responsible."

Comments

A reference on leap seconds

[Adam J. Richter]

The earth's rotation is slowing anyway. This is the reason that they insert those "leap seconds" every few years to compensate for the lost time.

At first, I did not believe that such a small change could account for the leap seconds, but you're right :

Through the use of ancient observations of eclipses, it is possible to determine the average deceleration of the Earth to be roughly 1.4 milliseconds per day per century.

[...] Over the course of one year, the difference accumulates to almost one second, which is compensated by the insertion of a leap second into the scale of UTC with a current regularity of a little less than once per year. Other factors also affect the Earth, some in unpredictable ways, so that it is necessary to monitor the Earth's rotation continuously.

In order to keep the cumulative difference in UT1-UTC less than 0.9 seconds, a leap second is added to the atomic time to decrease the difference between the two. This leap second can be either positive or negative depending on the Earth's rotation. Since the first leap second in 1972, all leap seconds have been positive and there were 22 leap seconds in the 27 years to January, 1999. This pattern reflects the general slowing trend of the Earth due to tidal braking.