The popular Geoclock and DX Atlas can be set up to give a reasonable
indication of start/finish of D or F layer illumination.
In Geoclock edit the GECONFIG.DAT file to include the following:
SUN
RemSUNLIGHT-0.833
RemTWILIGHT-6
SUNLIGHT-6.596
TWILIGHT-14.165
As most people know the "rem's" remove the lines giving the standard
settings for sunset and twilight and the following lines substitute the
approximate sun angle below the horizon where D-layer illumination
finishes/starts -6.596 degrees and F-layer illumination at -14.165 degrees
below the horizon. By reming out the lines it is easy to swap back
without having to remember the numbers.
In DX Atlas there is a setup option to select the Sun angle below the
horizon as Civil twilight (-6 deg), Nautical twilight (-12 deg) or
Astronomical twilight (-18 deg). So the D-layer illumination boundary is
close to Civil twilight and the F-layer illumination boundary is a little
after Nautical twilight.
Naturally this is all approximate as it depends upon the actual height of
the D and F layers at the time but seems to be good enough.
To quote Aristotle:
"It is the mark of an instructed mind to rest satisfied with the degree of
PRECISION which the nature of the subject admits, and not seek EXACTNESS
where only an approximation of the truth is possible."
Of course, "the degree of precision" etc. is a sliding window.
Regards,
Mike VP8NO
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