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Most bubble sextants will measure negative altitudes. My RAE MK IXA goes as
low as -13 degrees. My A-10 goes to - 2 degrees 55 minutes. I believe that
most marine sextants are also capable of measuring negative altitudes to at
least - 5 degrees.

A small clarification to my earlier comments regarding refraction in the
polar regions: your sextant would not yield a negative reading, the
calculated altitude would be negative. It is only at (height of eye)
altitudes of several thousand feet asl (as in an aircraft) that one would
observe a negative altitude.

Robert

----- Original Message -----
From: "Fred Hebard" 
To: 
Sent: Thursday, August 04, 2005 12:50 PM
Subject: Re: Refraction


> Marcel,
>
> OK, I got it.  Ignore my last post.  You might want to look at the
> Introduction to the Air Almanac, which should give instructions for its
> use, and should discuss this case.  I've never seen a bubble sextant,
> so I don't know whether they measure negative altitudes.
>
> Fred
>
> On Aug 4, 2005, at 12:20 PM, Marcel E. Tschudin wrote:
>
>> Yes, how do I get in this? Just trying to cover in a self-made program
>> the
>> situation from an object at the horizon (over sea level) as seen from a
>> mountain or air craft.

   

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