NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Use of Sun Sights for Local time, and Lunars for Longitude
From: Bruce Stark
Date: 2002 Oct 23, 18:36 EDT
From: Bruce Stark
Date: 2002 Oct 23, 18:36 EDT
It seems to me we're all pretty much in agreement that calculated altitudes are OK for clearing a distance. Now, perhaps, more lunars will be taken. On land it's so much more convenient to used calculated altitudes, and it only takes five or ten minutes to get a set of distances. I appreciate William Noyce and George Huxtable taking time to explain where the thirty-to-one reduction in error comes from. I also appreciate them pointing out that in most cases there's no need to repeat the calculations. Actually, there may be a better way of getting that thirty-to-one reduction in the error of the moon's hour angle than the one we've been discussing. Here's an excerpt from a posting William Noyce made last April: >I don't think you need to make any special "local apparent time" observations or calculations. Assuming the navigator >has been using celestial observations all along, but has an incorrect clock, he will have determined a celestial "fix" >whose longitude is off by almost exactly 15' for every minute of time error. These two errors will cancel out to >reduce errors in computed altitudes, the same way as Bruce Stark's procedure using local time. The remaining errors >come from the change in declination (pretty fast for the moon), and the difference in rate of change of GHA between >the sun, planets, and stars. Maybe some list members will check this out. Working from local time and shifting back and forth between arc and time isn't everyone's idea of fun. Bruce