NavList:

Of DeltaT, Omar R wrote:

"I wonder why can't this value be deterministic, like everything else in astronomy ?"

 

Can you predict the dust storms on Mars? How about the shape of the next sunspot? You would probably counter that those things are "weather" not astronomy. And I think that's basically how we define traditional computational astronomy. Anything that is subject to computation in the foreseeable future, we count in, otherwise it's out. Changes in delta-T derive from the complexities of the Earth's weather and its interior, channeling angular momentum from one part of the total system to another. The net angular momentum of the Earth, if we could measure it, presumably shows a much more "deterministic" decline since it's under the influence of the luni-solar tides. But even there, the exact damping effect depends on the shapes of the ocean basins (which are changing on a geological time scale).