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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Regulus Occultation, unexpected results
From: Paul Hirose
Date: 2017 Sep 30, 22:16 -0700
From: Paul Hirose
Date: 2017 Sep 30, 22:16 -0700
On 2017-09-30 18:03, Sean C wrote: > (I currently receive bulletins A and C: ΔT and leap second announcements, respectively.) This saves you from having to search for anything - the ΔT values are right there waiting for you in your inbox each week. Actually, delta T is not in IERS Bulletin A or B. To obtain it, evaluate the expression (TT-TAI) + (TAI-UTC) - (UT1-UTC) The first term in parentheses is the constant 32.184s. The second term is an integer, now 37s. It increments every leap second. Daily values of the third term are in the bulletins. Note that TAI and UTC both occur twice in the expression, but in opposite sign. Thus they cancel, and the expression simplifies to TT-UT1, alias delta T. The reason for the small discrepancy Sean detected in my UT1-UTC is that I didn't get it from the latest Bulletin A. I already had an older version at hand, and was confident the value found therein would be more than accurate enough. My Lunar4 program, if you select "auto delta T," uses the table in the Astronomical Almanac, section K. Outside the span of that table it applies the polynomials at the Espenak site.
