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    Re: Pub.249 Epoch 2020 is available.
    From: Frank Reed
    Date: 2018 Oct 31, 06:49 -0700

    Why six stars per LHA band? That, too, is a change from Pub.249 which lists seven stars.

    And I must reiterate that it is a mistake to list the stars' altitudes to tenths of a minute for an annual set of data. The tenths are meaningless for annual data since the stars move around by over half a minute of arc in that time. You should either switch things up and prepare monthly (or daily!) tables, or you should drop the tenths. Publishing garbage data degrades celestial navigation. It does not improve it.

    Incidentally, while looking at the USN "STELLA" celestial navigation software this past weekend, I noticed that they produce live, daily 249-equivalent data, as I previously recommended. It's the usual lists of stars (seven per LHA band, three "starred" as preferred for a three-body fix), but the data are not calculated for some arbitrary five-year epoch. Instead they are simply published for the current date. This, of course, permits arbitrary accuracy, and it also eliminates any need for the P&N tables. 

    Frank Reed

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