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Monday, September 19, 2005

Solar Eclipses over Egypt over the Millennia

[Note: updated and revised on October 13, 2005 to reflect the fact that Amir Bey's eclipse data for Egypt are still online.]

Fred Espenak has website pages covering historical and future solar eclipses at
NASA - Eight Millennium Catalog of Long Solar Eclipses
entitled:
"Eight Millennium Catalog of Long Solar Eclipses [by] Fred Espenak -2999 to +5000 (3000 BCE to 5000 CE) [covering the] eight Millennium period -2999 to 5000 (3000 BCE to 5000 CE[1]), [during which the] Earth will experience 18,988 solar eclipses.....[longest-lasting eclipses are listed]."

The exact dating and location of these eclipses is uncertain because of variations in the calculation of Delta T, the mathematical value for changes in the rate of the spin of the Earth over time, which is variable.
See Espenak, Espenak on Saros, David Herald, Felix Verbelen, and for comprehensive detail Robert H. van Gent.
Most recent values are found cited at Guide-User, where it is written by Bill J. Gray:

"Usual warning: Delta-T becomes increasingly ill-defined as you extrapolate it. For example, a decade or so ago, it looked as if Delta-T was going to keep increasing by about a second or so each year, requiring a new "leap second" each December. Then it stopped increasing so briskly, and we've not had a new leap second since 1999. The above formula is there simply because Guide has to say _something_ about what Delta-T is apt to be, even if that something isn't very
meaningful."


We have our own explanation for the slowdown in the increase starting at 1999 which we have posted elsewhere as well:

"One way to understand Delta-T better is to spot the cycles which may be incorporated within it. One of these may be solar luminosity - which may have a ca. 190-year cycle, as manifested in the delta-T values evidenced between ca. 1700 and ca. 1890.

As written at Inside Earth:
"A Master’s thesis on a broken stalagmite in the main cave indicates a temperature cycle of 190 years between ~13,500 and 9,500 years ago, most likely a solar luminosity cycle."

This in turn may relate to the cycles in sunspots

which in turn are related to geomagnetic activity.

In my opinion, these variations are caused by planetary perturbations viz. planetary positions varying between perihelion and aphelion.

If that were true, then primarily responsible for the ca. 190-year cycle would be Pluto (actually, the orbit here is 248 years as such), which was at perihelion until 1999, when it was still within Neptune's orbit.

Now Pluto is headed back out to be the 9th planet again.

Accordingly, if the above theory be true, Delta T should now slow down as it has done, stay constant at ca. +65 and then diminish, rather than increase. Of course even if we were right on this prediction, we could be wrong, since current theory is that the planets can not exert this kind of influence, but I am not so sure."


Solar eclipses are useful for chronology and potentially especially for the history of Ancient Egypt. See LexiLine and Amir Bey, Eclipses over Egypt.

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