NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Time Sights
From: Chuck Griffiths
Date: 2002 Jan 29, 11:33 AM
From: Chuck Griffiths
Date: 2002 Jan 29, 11:33 AM
First, bravo to Mr. Huxtable for his very lucid, learned, lunar distance dissertation. I'll work the examples this weekend. Looking forward to his part 3, I have a couple of thoughts about time sights. First, have others besides myself noticed the frequency with which this term is misused? In my mind, a time sight is a method of finding one's longitude by solving the navigational triangle for meridian angle knowing codeclination, coaltitude, and colatitude. I've noticed several writers using the term for something else as the original time sight falls into disuse. I offer the following as an example: From Marine Navigation by Richard R. Hobbs 3rd ed. pg. 455 "When a very high degree of accuracy in the latitude line is required, many navigators construct a graph such as that shown in Fig. 25-2 (The figure shows altitude plotted against time during a meridian sight.) to assist in picking the precise altitude of transit. Such a series of sights is called a time sight..." I find this example interesting for two reasons. First, as mentioned previously, this is not my idea of a time sight. Second, Hobbs doesn't go on to describe how the resultant graphically determined time of meridian passage can be used to find one's longitude to produce a lat-long fix from the noon sight. Granted, it's not the best longitude fix, but if one goes to the trouble of graphing one's noon sight observations one might as well use it to the best effect. My second point for discussion is tables for solving real time sights. Bowditch (pre-1995) offers a history of such tables, sometimes referred to as horary tables, but I have never seen an example. Does anyone out there have an example of any of these that they could scan and post? I thought it might be a nice supplement to the discussion of finding longitude. Chuck Griffiths ********************************************************************** This e-mail and any files transmitted with it are confidential and may be legally privileged or otherwise exempt from disclosure under applicable law. This e-mail and its files are intended solely for the individual or entity to whom they are addressed and their content is the property of Smiths Aerospace. If you are not the intended recipient, please do not read, copy, use or disclose this communication. If you have received this e-mail in error please notify the e-mail administrator at postmaster@si.com and then delete this e-mail, its files and any copies. This footnote also confirms that this e-mail message has been scanned for the presence of known computer viruses. ***********************************************************************