NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Jupiter Lunar DSLR Camera Trial
From: Paul Hirose
Date: 2010 Nov 11, 13:14 -0800
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. --