NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Leap second today
From: Lu Abel
Date: 2012 Jun 30, 15:17 -0700
From: Lu Abel
Date: 2012 Jun 30, 15:17 -0700
With respect, let's remember that the NA is generated from mathematical formulae, calculated on a computer and then printed.
I have seen at least one instance of on-line NAs being off in the last digit as compared to the printed NA. The way the computer does its math can affect the result, even if it is calculating from the same formula.
A good non-computer example is the old HO211 sight reduction (or the new NA version), where doing calculations at certain values of data is discouraged, typically because you are finding difference between two large and nearly equal numbers.
Even more important, though, is it worth worrying about the
NA's accuracy due to the leap second? CelNav typically gives us positions to 3~5 nautical miles, with everything from sextant error to heaving seas to indistinct horizons making it difficult to get Hs's to within a minute. So if there's a NA error of 0.1' due to the leap second, who's to notice?
From: Brad Morris <bradley.r.morris@gmail.com>
To: NavList@fer3.com
Sent: Saturday, June 30, 2012 1:42 PM
Subject: [NavList] Re: Leap second today
Since no one appears to have answered Frank's question, I will.Frank asked "is your Nautical Almanac now always wrong or always right"The answer depends upon how the NA is structured. The NA is essentially a table, with the independent variable the time, and the dependent variable the celestial coordinates of the object in question.Since the leap second corrects the time, when we enter the NA, it provides the correct coordinates for that time.The NA remains as correct as it wasOn Jun 30, 2012 4:34 PM, "bill" <billyrem42@earthlink.net> wrote:On 6/30/2012 2:13 PM, Lu Abel wrote:
Or folks can go to www.time.gov to watch the clock. I've done it for a
past leap second and the NIST clock does indeed show the sequence
(especially the 7:59:60) Frank describes.
I suspect my atomic clock that synchronizes to WWVB will not show the
sequence, but simply reset itself, but Frank has be curious. 5PM for
us West Coasters.
I do plan to video the NIST computer clock at 8 PM EDT as well as listen to the ticks (new UTC to UT1 double clicks).
As my RCC attempts to sync at midnight mountain time--2 AM EDT-- I imagine the NIST broadcast time and time displayed by my RCC will be out of sync (past the regular drift) for four hours. I will video the 2:00 reset as well to see if the RCC does a 02:59:60, 02:00:00 reset.
My real concern is whether I will be sluggish and disoriented (more than usual) the day after due to the time change ;-)
Bill B
