I think you might be being a little disingenuous? You could and likely have looked up information about that which you ask. However
The great year is known very well with
> good accuracy, as for all other motions of
> Any chance that you could explain just how
> accurate this knowledge is? Or, are we just
> expected to take your word for it?
Even the simple wiki article on the subject Axial Precession is rather comprehensive about what is known
> You can start with the Rate of Precession. Is it
> constant, speeding up or slowing down?
Apparently at the moment it is very (extremely) slightly speeding up
> Then, lead into the number of measured Great Years
> and the methods used to calculate the verified
You know darned well there is no known evidence of any civilization lasting for 26000 years and recording periodic precessions. The estimate is made by observing smaller chunks of time.
> Please keep to the Scientific Method with your
> data being measurable, testable and repeatable.
> Can you do that?
Clearly in modern times (read wiki entry) extremely accurate observations have been made since year 2000 CE (again small chunks) Also read the admission that science does not know if the rate will increase or decrease but there is little reason to suspect it would be a massive departure from the range observed for well since the Greeks 2000 plus years ago.
I am guessing you think scientific method is restricted to physically observable experiments and observations?
There are many areas of modern science where physical experimentation is impossible. Astronomy (as you likely already know) bases much of its science on assumptions.
Even for example, no one has accurately measured the speed of light (and therefore one of Einstein's key postulates) outside of our solar system. Rather they make further assumptions such as on such things as pulsars and their size etc to try to measure it. But they obviously do not go out there with a tape measure and a clock.
Hope that helps?