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    Navigational Stars: numbers and SHA
    From: Frank Reed
    Date: 2012 Nov 27, 13:29 -0800

    Here's a trivia challenge for you.

    Each of the 57 navigational stars has a number. Alpheratz is 1, Ankaa is 2, Schedar is 3, and so on down to Markab which is numbered 57. Originally the stars were listed by Right Ascension or RA, which navigators used instead of SHA through the 1930s when practice began to change. The numbers for the stars were assigned by order of RA. But SHA runs the other way. If both are measured as angles, SHA=360-RA. So in the Nautical Almanac tables, the stars listed by numerical order are nearly in reverse order by SHA. But not quite! Thanks to precession, the order of the stars can change. In the early 20th century, the numbers of the stars were changed when the order changed. That was a bad idea, and the numbers are now fixed. But precession continues, and two of the stars, in order by number, are no longer in order by RA (or in reverse order by SHA).

    The challenge: Name the two stars that are no longer in order by RA/SHA when listed in standard numerical order. To save you some time, the name of one means "Southern Claw". For a bigger challenge, in what year did they swap places?

    -FER
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