NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Chronometer Suggestions
From: Gary LaPook
Date: 2009 Jan 6, 13:15 -0800
From: Gary LaPook
Date: 2009 Jan 6, 13:15 -0800
Make sure you go to the July 23 post not the July 25 or July 30 posting. http://groups.google.com/group/NavList/browse_thread/thread/a270bc3d6aeb66d4?hl=en gl On Jan 6, 12:48�pm, glap...@PACBELL.NET wrote: > You don't have that exactly right, the LOP moves westward one minute > of arc every four seconds, not one nautical miles. Since the length of > one minute of longitude varies as the cosine of the latitude the > distance the LOP moves also varies by the cosine of the latitude. At > the equator the length of one minute of longitude is one nautical mile > but at 60� latitude it is only one half of a nautical mile. > > In addition to this, the amount of change in altitude also varies with > the sine of the azimuth so you have to combine these two factors. Go > to : > > http://navlist.googlegroups.com/attach/c09c132c9a92fad1/HO+249+extrac... > > which contains two tables called "motion of the body" or "M.O.B." > tables that are used in flight navigation to allow for the motion of > the body. Look at the table for four minutes. Since four minutes of > time is 60 times four seconds of time just divide the tabulated values > by 60 to obtain the change of altitude in four seconds of time. (Or > you can just consideer the tabulated values as seconds of arc.)For > example, the first value listed is 60' for latitude zero and azimuth > 90�. Go accross the top line to 60� latitude and you will find that > the change in altitude is 30' exactly one half of the change at the > equator and which would result in a change of 30 NM in the intercept. > > Go to my July 30, 2008 post on the "Celestial up in the air" thread > for further explanation at : > > http://groups.google.com/group/NavList/browse_thread/thread/a270bc3d6... > > gl > > On Jan 6, 12:20�pm, "Federico Rossi"> wrote: > > > Lu, > > > If I�ve understood well, this error doesn�t depend on your latitude on > > earth, i.e. it�s a maximum of 1 nm for every 4 seconds (for bodies due east > > or west) whether you are on the equator or far from it, does it? > > > Federico > > > Da: NavList@fer3.com [mailto:NavList@fer3.com] Per conto di > > Lu Abel > > Inviato: marted� 6 gennaio 2009 20.05 > > A: NavList@fer3.com > > Oggetto: [NavList 6941] Re: Chronometer Suggestions > > > Irv and Bill: > > > It's a MAXIMUM of 1 NM for every 4 seconds, not a minimum. � > > > If the body you're sighting is directly north or south of you, even a fairly > > significant time error would result in a very minimal shift in the LOP > > produced by the body (the extreme example is Polaris). � On the other hand, > > if the body you're sighting is directly east or west, then it's Geographic > > Position is moving by 1 NM every four seconds and any LOP developed from > > that sight would be off by 1 NM for every four seconds of clock error. > > > Lu Abel > > > Irv Haworth wrote: > > > Minimum of 1 NM for every 4 seconds..( a quick answer).. > > > Irvin F Haworth > > > W, Van BC Canada > > > � _____ � > > > From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf > > Of William Sellar > > Sent: January 6, 2009 5:05 AM > > To: NavList@fer3.com > > Subject: [NavList 6931] Re: Chronometer Suggestions > > > As a beginning celestial navigator, I am wondering how much time and watch > > accuracy is actually required for practical navigation. �Can we predict how > > many miles off one would be for every second of time error? > > > Bill > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---