NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Faint stars easier to find on the horizon first?
From: Henry Halboth
Date: 2004 May 31, 21:25 -0400
From: Henry Halboth
Date: 2004 May 31, 21:25 -0400
You bring up a very good point - pre-computation of altitude and azimuth seems to be a neglected wrinkle in practical navigation and is barely mentioned in most navigational texts to which I have quickly referred. On short notice, I can point out only one clear reference in Bowditch, 1958 edition, under a description of the Rude Star Finder (HO 2102-D), where the statement is made under customary usage to the effect ... "To make an advance list of celestial bodies available for observation at a given time." Lecky does stress precomputation with respect to stellar meridian altitudes but does not seem to carry it the logical step forward. As indicated in Bowditch, I started precomputing by means of the Rude Star Finder, but after publication of HO 249 found this pub far more convenient for the purpose. It should probably be mentioned that in bygone years the possible error in DR positions may have been great enough to negate some of the advantages of precomputation, but I can assure you that an error of as much as 20 miles will make little difference - also the amount of math necessary prior to the advent of modern star finders and tables probably affected popularity. I suggest that you do a little experimenting, starting with Polaris on a clear evening, and you will quickly be convinced. On Sat, 29 May 2004 17:06:13 -0300 Jim Thompsonwrites: > Henry, this is a very important practical point for us beginners. > The > concept never came up at all during our course, and if it is in > Bowditch or > Dutton's, then I missed it. > > Jim Thompson N > jim2@jimthompson.net > www.jimthompson.net > Outgoing mail scanned by Norton Antivirus > ----------------------------------------- > > > -----Original Message----- > > From: Henry C. Halboth > > good star/planet sights require pre computation of altitude and > > azimuth which generally allows observations of the brighter stars > and > > planets within 5 to 10 minutes before/after sunrise/sunset, > depending on > > Latitude. You will never be successful in obtaining star fixes if > you > > wait to see the body with the naked eye >