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Gary Lapook wrote, in response to a posting by Henry Halboth-

You might be surprised by the level of accuracy in determining the longitude
from equal altitude sights:
http://articles.adsabs.harvard.edu//full/1919PA.....27..359W/0000359.000.html
http://articles.adsabs.harvard.edu//full/1919PA.....27..359W/0000363.000.html

(most of the "meat" is in the first of these links)
=====================

Comment from George-

This was an interesting 1916 paper which, in part, describes the preliminary
determination by sextant of the location of an observation station near
Baker, Oregon, which later became accurately known by precise astronomy.

It was made using equal altitudes of the Sun, presumably (though we are not
given such details) using an artificial horizon.

I don't think anyone should be surprised by the accuracy achieved. Indeed,
it was worse than they expected, being out by about 1 second of time (15
arc-seconds) in longitude, and nearly half a minute in latitude. This,
despite many averagings over several days, with none of the uncertainties
that arise when looking at a real horizon from the deck of a vessel.

Although it's been posted under the threadname "Lat/Long by Noon Sun", it
really had nothing to do with a noon Sun. The author tells us that his equal
altitudes were taken in the forenoon and the afternoon, without stating
exactly what time. But I suspect that they were made several hours apart, so
that the two Sun azimuths differed by somewhere near to the optimum angle of
90 degrees.

They ended up suspecting that errors in the latitude could be due to
inaccuracies in their Brandis sextant, though that shouldn't affect the
equal-altitude longitudes.

I'm unsure about the lessons that Gary expected us to draw from that paper
(he didn't say) but it tells us nothing about longitude-around-noon (except
that it's avoided when precision is called for), and had no relevance to the
points Henry was making.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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