# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: The rapid-fire fix**

**From:**John Karl

**Date:**2009 Apr 27, 14:39 -0700

Frank, I don't understand the sight reduction of your "quick fix". You start with one (averaged) altitude at 0930 and get the longitude by a time sight. But longitude by a time sight requires some other info, normally the latitude, which is not known. So what am I missing here in your discussion?? Then you get the latitude form the two sights at 0910 and 0950. I do understand how this is possible because we now have two pieces of information, two H's and the time interval. For example, using the Sin (H) altitude equation, the two unknowns are one latitude and one LHA (the second LHA is not another unknown because it is the original LHA + earth-rate * time). However, these two trig equations in two unknowns would be tricky to solve explicitly, maybe impossible, but certainly numerically. I don't understand your explanation of "using the rather complicated methods found in most 19th century navigation manuals, we would get latitude from the two altitudes and the time interval between them." Are you referring to something like I just discussed? On the other hand, there is explicit method in my book on pp 78-79, eqs 7.5. These are a simple, understandable, application of the familiar H and Zn equations. The method uses only one more trig equation than two St. Hilaire LOPs. And it gives both Lat and Lon explicitly, without requiring tables or the 0930 calculation. --JK --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---