Thanks so much Bill. I feel like I just discovered Staples' EASY
button. Not only does it work as advertised, but I'm relieved to
find that my now marked crash zone is really pretty small.

Pete Peterson

--- In guide-user@yahoogroups.com, Bill J Gray <pluto@...> wrote:
>
> Hello Bernd, Alan, Pete,
>
> I think I must have been having an "off" day when I answered
Alan's
> question, because there's a simpler way of doing this. For his
> situation (adding a fixed zone around the zenith of radius 23
degrees),
> one would add these lines to 'horizon.dat':
>
> c 2
> 0 90 23
>
> For Pete's situation, needing a circle of radius 18 degrees
around
> the North Celestial Pole, that would change to
>
> c 2
> 0 44.01 18
>
> For '44.01' (my latitude), substitute your own latitude, of
course!
>
> In both cases, one is simply adding a circle of given radius
to a
> particular alt/az point. The zenith is at alt=90, az=0 (*), and
the
> north celestial pole is at alt=latitude, az=0.
>
> Pete, you also mentioned: "... Being able to mark the viewing
> constraints, such as the neighbor's tall elm tree, would simplify
planning."
> This can also be done. By default, 'horizon.dat' shows assorted
objects
> scattered around the horizon, such as trees, houses, etc.
There's
> some documentation at the bottom of the file describing how you can
> move, add, scale, etc. these objects.
>
> If you're feeling truly energetic, you can even add your own
objects;
> see 'objects.nam' for examples and, near the end, some (admittedly
> minimal) documentation. I don't know if anyone has actually done
this;
> the objects already supplied are probably enough for most needs.
>
> -- Bill
>
> (*) OK, in reality, the azimuth at the zenith is undefined, and
you
> can use any value you want there; it won't affect how the program
> does things.
>