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    Re: Dropping leap seconds and the impact on celestial navigation
    From: Fred Hebard
    Date: 2011 Sep 10, 12:24 -0400

    Frank,
    
    I can offer no opinion on the navigational aspects of this, but I wonder what 
    will happen 200 years from now.  Will noon be 11:30 am?  That would be 
    unacceptable to me.  Is it really that difficult to keep the leap seconds 
    convention going?
    
    Fred Hebard
    
    On Sep 8, 2011, at 10:00 PM, Frank Reed wrote:
    
    > I have committed to do a presentation at the colloquium next month in 
    Pennsylvania (Oct. 5/6) regarding the proposal to drop leap seconds from the 
    definition of UTC. One of the things that I want to do is get opinions from 
    NavList members. Suppose leap seconds are dropped from time-keeping. Since 
    the Earth's rotation does not quite match the definition of the second, the 
    Earth's rotation will slowly fall out of line with the mean times kept on the 
    vast majority of the world's clocks. If this proposal takes effect, then, in 
    the year 2025 for example, if you calculate when the star Sirius crosses the 
    meridian at your location naively using UTC, you might find that it is seven 
    or eight seconds late. Similarly "local noon" would not occur at twelve 
    o'clock, even on average, even at the center of a time zone. This is easily 
    observable, and this sort of discrepancy could easily put a vessel's position 
    out by a couple of miles. Of course this would only happen if we were to 
    BLINDLY apply the rules without correction. The simple solution is to include 
    a table in the annual Nautical Almanac and other "nautical almanac" 
    equivalents giving the "watch error" of UTC relative to navigators' time 
    (whatever that might be). There might be other ways to handle this, too. In 
    principle, this should be no problem. In practice, there may be serious 
    education issues. Since celestial navigation is primarily a backup method of 
    navigation, and many people who would use it in an emergency could be fairly 
    described as "rusty" on the details, would a navigator so be confused in an 
    actual case where the methods were needed that navigation would be 
    compromised?
    > 
    > I would like to get as much input on this as possible. All opinions welcome! 
    I need to finalize my presentation within the next couple of weeks, so start 
    thinking and get back to me as soon as possible. Naturally, I will give 
    individual credit where credit is due (for any non-obvious ideas!) and 
    general credit to the NavList membership for your help.
    > 
    > -FER
    > 
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