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: Joel Jacobs
Date: 2004 Jun 2, 05:52 -0400
From: Joel Jacobs
Date: 2004 Jun 2, 05:52 -0400
List member Bob Enro wrote me some time ago about a different type of star finder he has. He wondered if I knew anything about it. I do. It was one of Nautech's very special products. It is very different from the Rude star finder since it has a moveable index arm which allows the template to slide up or down in one degree increments for intermediate LAT between the 10 degree separation on the template. The arm also allows the selection of DR LON, and calculates LHA. The major advantage was the ease of plotting planets on its face, and the precise ALT and ZN estimates it gives. I'm surprised we haven't heard from Bob on this. Here is a portion of my answer to him. You are one lucky person. There can't be many of those floating around. It should be worth a lot of money to the right person who collects militatria since it was originally used to set the guidance system of a missile. The instructions, I hate to say were not great I haven't played with one of those in years. Here's what I remember. The inner ring is graduates of GHA, SHA and Aries in 1 degree increments. Whichever you want. The outer moveable ring is LON. If you set GHA object over Greenwich which is 0 on the outer ring, and move the cursor to you DR LON on the outer ring's scale, the inner scale gives you LHA object. This lines up the template so that all the bodies are in their correct ALT and AZ from you located at the center of the template in the little hole, not the grommet. The azimuths are the radial lines and the altitudes are the parallel lines on the templates. The largest parallel line is the limit of the visible horizon. Because the templates slide up and down you can get set your DR LAT much closer to the real position so that the ALTS and AZ to body are much more precise than with the HO 2104 D Rude Star finder where you DR can be off as much a 9 degrees. The Rude is still sold today. I used to be quite good with that puppy and really used it daily to set up the sequence of my sights. It made plotting planets a snap. I hope my memory is correct, and this helps, Joel ----- Original Message ----- From: "Henry C. Halboth"
To: Sent: Monday, May 31, 2004 9:25 PM Subject: Re: Faint stars easier to find on the horizon first? > 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 Thompson > writes: > > 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 > > email@example.com > > 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 > >