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    Dropping leap seconds and the impact on celestial navigation
    From: Frank Reed
    Date: 2011 Sep 8, 19:00 -0700

    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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