NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Star sights on reciprocal bearings
From: Paul Hirose
Date: 2006 Dec 10, 13:33 -0800
From: Paul Hirose
Date: 2006 Dec 10, 13:33 -0800
Geoffrey Kolbe wrote: > > "Hints for Travellers", published by the Royal Geographical Society, > (about which there was some discussion recently when Frank Reed > pointed out that the 1906 edition was up for auction on ebay and I > successfully bid on it), details the methods by which a surveyor may > fix his (or her) position to within a few seconds of arc. The > underlaying principle is to take sightings of bodies in opposition > (North-South for latitude, East-West for longitude) in order to > reduce systematic error - principally in how level the theodolite is. How would these paired observations reduce the effect of leveling error? It seems to me that if the theodolite vertical axis is inclined say 1 minute to the north, then a star to the north will measure 1′ too high and a star to the south will measure 1′ too low. The leveling error has not been eliminated: both observations agree that you're 1′ north of the true location. On the other hand, reciprocal sights would reduce the effect of refraction error. I've read that precise latitudes were obtained on land from precomputed pairs of stars which crossed the meridian at nearly the same time, high in the sky, at almost identical distances north and south of the zenith. -- I block messages that contain attachments or HTML. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---