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    Re: Jupiter Lunar DSLR Camera Trial
    From: Paul Hirose
    Date: 2010 Nov 11, 13:14 -0800

    Antoine Couette wrote:
    > I keep mentionning the exact "TT-UT" 
    > value I'am using whenever I publish data about my computed results. This 
    > remains the ONLY WAY - and by the way, do you see any other one ? - to 
    > help other "number crunchers" (I now know of at least 3 different ones 
    > now just on NavList Forum) to meaningfully check their own results 
    > against mine.
    It is helpful to state ∆T, but not always necessary. For dates in the
    past, ∆T can be calculated from the monthly IERS Bulletin B
    (http://hpiers.obspm.fr/eop-pc/products/bulletins/bulletins.html). For
    example, at 2010-09-22 0 hours, UT1 - UTC = -.057 seconds. The Bulletin
    also says TAI - UTC = 34 s.
    Because UT1 is .057 s behind UTC and UTC is 34 s behind TAI, UT1 is
    34.057 s behind TAI. And because TAI is always 32.184 s behind TT (by
    definition), UT1 is 66.241 s behind TT. So ∆T = 66.241 s.
    Dates too recent for Bulletin B, and dates up to 1 year in the future,
    are in Bulletin A
    (http://www.usno.navy.mil/USNO/earth-orientation). (The link is in the
    "Popular Products" box on the right.) Bulletin A also has the values for
    TAI - UTC and TT - TAI.
    Nevertheless, if you always give ∆T it does eliminate some work and
    uncertainty for others.
    I filter out messages with attachments or HTML.

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