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On my opinion,
the ideal distance is determined by 2  (sometimes opposing) factors.

1. Geometric configuration (you want the distance to change as
fast as possible. You want refraction to be as small as possible).
For this the distance and the altitudes have to be large enough.

2. Convenience of observation. This is something that depends on
your instrument. And skills. Observation of very large distances is
more difficult.

From my experience the range 40-80 is the most convenient and gives the
results of about equal accuracy. So there is no optimal distance.
All distances in this range are equally good.

More important is the angle between the great circle on which
the bodies are and the horizon.
With modern sextants (handle on the right) and right handed people,
the convenient angle is about 45 degrees when the higher body
is on the right of the lower body.

It is very inconvenient to hold the sextant
inclined in the opposite way.
Also inconvenient when the altitudes are high,
but on the other hand in this case we have less refraction.

If the altitude is high and or the angle is inconvenient, the best thing
I can do is to lay on the deck (floor of my balcony:-)


Alex.




> That's so weird...just yesterday I was wondering what (if any) is the
> "best" angular separation for a lunar. And now I see this discussion.
>
> An internet search and a browse through Bowditch did not turn up much. So,
> may I add to Brad's question and ask, "What IS the ideal separation for a
> lunar?" Or are all [sufficiently large] angles equally accurate?
>
> Thanks,
> Sean C
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