Next message: Marcel E. Tschudin: "Re: Refraction"
George wrote:
>
> By the way, several of those responses from Roibert Ene were misdated to
> have a September date rather than an August one. I hope he will correct
> his
> calender, because my email reader, which puts correspondence into strict
> date order, keeps mis-sorting Robert's contributions.
>
> ==============
Yes, thanks George. I caught that yesterday and made the change. Don't know
how it got advanced a month.
George wrote:
> That seems a bit odd, and unphysical. From a height of 0 feet, how can a
> sextant altitude possibly be -1degree? Also, the quoted value for the
> correction, at -35 minutes, is rather a surprise, considering that the
> adopted value for refraction at 0 degrees altitude is -34 minutes, and
> refraction increases very quickly as the altitude decreases towards zero.
Robert responds,
Quite correct George. The entry arguments for the altitude of the observer
are in increments of 5000 feet, starting at 0. So those refraction figures
that I quoted apply (presumably) to altitudes of from 0 - 4999 feet.
Obviously this is a table for air navigation, so I would imagine that the
corrections were intended for altitudes well above sea level.
Robert
