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    Re: Dropping leap seconds and the impact on celestial navigation
    From: Frank Reed
    Date: 2011 Sep 10, 22:59 -0700

    John H, in another post, you asked:
    "Do we end up with leap minutes instead of leap seconds?"

    I believe the current proposal is for leap hours but enacted by regional legislation in much the same way that time zones and DST are enacted. As I noted in my other message, the easiest way to shift west by an hour is to skip the "Spring Ahead" step in DST for one year while retaining the "Fall Back" step later in the year.

    Here're another economic issue: suppose we write an insurance contract that expires at 6pm Eastern Time on March 1, 2015. From the current time, how many seconds is it until that contract expires? Easy, right? Well, no. Because we don't know how many leap seconds will be inserted between now and then. This is not an issue for calculating some exceedingly exact insurance premium. But it does become an issue when we try to do quality control and double-check accounting figures. The exact interval between some present instant and future dates in UTC is currently UNKNOWABLE.

    You concluded:
    "I still like the idea of having mean solar time under any circumstances, realizing that in a given year it won't be perfect."

    We can still have mean solar time. All we need is a table published annually giving the offset in seconds for the year (or for various dates in the year). I mentioned above that this can't be predicted, but for one year ahead, for the use of celestial navigation, it can be listed with some confidence (since mostly this would be the accumulated total from previous "skipped" leap seconds). It's worth noting that most navigators, both experts and "cookbook practitioners" commonly refer to UT as GMT though these are no longer identical. Perhaps navigators could lay claim to the expression GMT permanently. Or perhaps we should invent a new term, maybe "GNT", for Greenwich Navigational Time. This would be that proper "mean solar time" that we would remain tied to the observed position of the Sun.

    -FER


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