Hi Bill, Steve, and all,

> Remove redundant Fortran function
>
> lib/hopping.f90 has been superceded by  C/C++ code except for the call
> to grayline() which is now called directly. 
> http://sourceforge.net/p/wsjt/wsjt/5545/

Thanks for all the recent good additions to WSPR-mode functionality. 
I've been temporarily buried in thinking about EME Echo mode...

The commit comment about my grayline() routine reminded me that I wanted 
to seek input on how our grayline range should be defined.

As a placeholder, in the present routine grayline.f90 I defined the 
grayline to be centered at the time when the sun is 50 arc minutes 
(0.8333 deg) below the local horizon.  This is normally taken to be the 
time of sunrise or sunset.  Of course, for ionospheric propagation 
purposes what matters is whether the sun illuminates a specific layer of 
the ionosphere.  The end of D-layer illumination occurs when the sun is 
something like 6.6 deg below the horizon.  (The end of F-layer 
illumination more like 14.2 deg below the horizon, but I think it's 
D-layer absorption that we're most concerned eith here.)

So...  would it be better to center our grayline periods at the times 
when the sun is about 6 degrees below the horizon -- also the end time 
of what's normally taken to be "civil twilight" ?

        -- Joe, K1JT

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