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"Agreed, but I thought the original question  was  whether you could fix your
position anywhere in the world with  celestial without having an initial DR
or EP (I  guess technically since it  wasn't specified originally that could be
interpreted  to mean either with  or without a sextant...)."

Right. My point is that you will always have  an excellent estimate of your
position, just by looking straight up.

"1)  Without a sextant (or some other reasonably  accurate measuring device),
 where exactly is the zenith? Dunno about you, but my  neck isn't exactly
calibrated in degrees - and if I recall correctly, that's the  main reason  that
we measure up from the horizon instead to find altitude (and it  gets
converted to co-altitude "automatically" either with tables or using a
mathematical formula so arranged to take that measurement into   account)."

As you noted, a meridian sight of any known celestial body  with a sextant is
scarcely more complicated than the simple "zenith sight" and  you get
latitude accurately, longitude somewhat less accurately. That's a  position from one
sight (better yet a brief series of sights) and no DR or AP  required as an
input, so long as you have a watch that's reading GMT or a known  zone time.

"2) Assuming that an  observer can find their zenith  accurately, what if no
celestial objects happen  to transit their GP at  that particular time of the
year?"

At night, under a dark sky, you can  still get a very good estimate of the
Dec and SHA of the zenith if you have a  basic star chart. Good enough, at
least, so that you would know your location  within a degree or two easily.

-FER
42.0N 87.7W, or 41.4N  72.1W.
www.HistoricalAtlas.com/lunars

   

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