NavList:

RE :
http://www.fer3.com/arc/m2.aspx?i=115594
[NavList] Re: 2011 Nautical Almanac
From: pmh099---com
Date: 7 Feb 2011 19:58

Hello Andres,

That's a difference of less than one second from 67.2s, which is hardly detectable for our purposes, so either value will work OK.

Peter Hakel

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From: Andres Ruiz <navigationalalgorithms---com>
To: NavList@fer3.com
Sent: Mon, February 7, 2011 5:05:06 AM
Subject: [NavList] Re: 2011 Nautical Almanac

Hello Kermit and PH!

If no approximation for Delta T is used:

Delta T = 32.184 s + (TAI - UTC) - (UT1 - UTC)
Bulletin C: from 2009 January 1, 0h UTC, until further notice : UTC-TAI = -34 s
Bulletin D: 6 January 2011, 0h UTC DUT1 = (UT1-UTC) = -0.2 s

So Delta T = 66.384 s

Is OK?

http://maia.usno.navy.mil/

Regards,

--
Andr�s Ruiz
Navigational Algorithms
http://sites.google.com/site/navigationalalgorithms/

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Dear Peter and Andr�s,

Yes, I agree with everything both of you indicated.

We can have a "super accurate" DeltaT value through proceeding as you have shown Andr�s. It would also imply computing the Moon Coordinates in the TT/TDT time scale with an accuracy better than 0.5" . It can be done, and in the case you want to "choose" just one Celestial Body, the ELP 2000xx Theory(ies) truncated to reach 0.5" overall accuracy take(s) up MUCH more space than a truncation to 6".

For my own use - and as ealier mentioned on this Forum - I am using a "canned version" of DeltaT which can be found here : http://eclipse.gsfc.nasa.gov/SEcat5/deltatpoly.html . Peter, don't you use the same TT-UT source ?

Such version is expected/believed to be accurate to +/- 1 second of Time from the/some remote past until nowadays. But, both for the past and for the future I always prompt for a TT-UT value in my programs to cover cases when the User needs to use his "own" value, including TT-UT = 0 if he wants to compute in the TT/TDT/ET Time scale for comparison whith more accurate sources.

Best Regards from Kermit

Antoine M. "Kermit" Cou�tte

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