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    Re: When is the Autumnal Equinox?
    From: Peter Hakel
    Date: 2011 Sep 3, 11:51 -0700
    In the attached first two screenshots note the declination rounded to 0d 00.0' with the sign switching from "N" to "S" in cell D5.  On 23 September 2011 Sun's declination crosses zero between 09:04:30 and 09:04:31 UT, with the latter instant giving the smaller absolute value of declination "Delta" in cell B60 (the third attachment).  Also note the 180d value of right ascension in the neighboring "Alpha" cells.

    Please see my blog for an analogous discussion of the summer solstice 2011:

    Peter Hakel

    From: Lu Abel <luabel@ymail.com>
    To: Navigation <NavList@fer3.com>
    Sent: Saturday, September 3, 2011 10:36 AM
    Subject: [NavList] When is the Autumnal Equinox?

    If one goes to the US Naval Observatory web page http://aa.usno.navy.mil/data/docs/EarthSeasons.php it shows this year's Autumnal Equinox at 0905 UT on 23 September.

    Whipping out my Nautical Almanac,  I find that the Sun's declination is 0d 00.1m N at 0900 and 0d 00.9m S at 1000.    A simple interpolation would put the Sun's declination at exactly 0d 00.0m at 0906 UT, not 0905. 

    Is this perhaps due to rounding in the NA data (eg, if the Sun's declination is either a tad less than 00.1' N at 0900 or a tad more than 00.9 S at 1000)??

    While on the topic, does anyone know of a site that gives the equinox down to the second??  (just curious)





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