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    DeltaT fits, WAS: Sun Moon Lunars to 155 degrees
    From: Peter Hakel
    Date: 2010 Apr 3, 12:36 -0700
    Dear Antoine,

    You already probably know of this, but here it is anyway, for DeltaT I use the following:

    http://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html

    It goes way back in time and I assume (!) that this is as accurate as possible with today's knowledge, coming from a NASA site.  Perhaps other members may correct me on this, if they have information to the contrary.

    I found this site sometime last year after Frank alerted me that using a currently valid DeltaT formula would result in unacceptable errors for historical lunars.  After I implemented these fits he then reported that this problem was solved, so I'd like to think that we are in safe waters with them.  Now he may be using these very same DeltaT fits :-) but his ephemeris come from a different method.  I use the French analytic theories that you know so well.

    BTW, I wonder how these fits get to be updated in case astronomers decide to add or skip any future leap seconds compared to what our presently expected evolution of Earth's rotation rate is.


    Peter Hakel



    From: Antoine Couette <antoine.m.couette{at}club-internet.fr>
    To: NavList@fer3.com
    Sent: Sat, April 3, 2010 10:16:15 AM
    Subject: [NavList] Re: Sun Moon Lunars to 155 degrees

    However, and just and only for our potential Number Crunching addicts - and I am aware of a few of them -, and although these dela-T values are not strictly necessary given their small amplitude just for the period of our Lunars (full agreement between us on this point) I am just publishing the delta-T values I have used here simply because :

    - I am not sure that they are widely available everywhere and anywhere yet,

    - they are still subject to some uncertainty, and will likely remain so indefinitely, which means different Number Crunchers can use different delta-T values, and

    - it is better "in principle" (or certainly "not worse") to use them to convert the TT scale "INTO" our currently best reconstruction of UT rather than to deliberately keep using TT "INSTEAD OF" UT while discarting such readily available values which have required so many huge efforts to reconstruct from historical data.


    [parts deleted by PH]


       
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