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Re: 1901 May, 22 Lunar example by French Navy Captain Arago
From: Paul Hirose
Date: 2010 Feb 06, 16:46 -0800
From: Paul Hirose
Date: 2010 Feb 06, 16:46 -0800
Antoine Couette wrote: > Your "reworked" results are > probably the most accurate ones achievable given the Ephemeris sources > you are using. The only remaining significant improvement would be > taking in account the Limb irregular shape (see F.E.R.'s comments just > hereafter). I can make one small improvement. The Astronomical Almanac eclipse predictions have adjustments of +.5" in the Moon's longitude and -.25" in latitude to correct for the difference between its center of mass and center of figure. My program has an option to apply that adjustment, but I normally disable it to make the output compatible with other programs. With the option enabled, the occultation is 1.7 seconds earlier. In Paris astronomical time, the results are: 10:53:17.3 Arago 10:52:59.3 Hirose (no corrections) 10:52:57.6 Hirose (with corrections) > You are right, "les hauteurs varies" mean "Unrefracted altitudes", i.e. > as they would be observed from Earth Center and without any Atmosphere > (no refraction). However, I thought "les hauteurs vraies" were the *topocentric* unrefracted altitudes of the centers. With that assumption I got: 1901-05-22T22:20:33.83 UT1 1901-05-22T22:20:32.93 Terrestrial Time -0.907 seconds delta T +47°49'33.2" - 79°37'22.8" north lat, east lon The new, correct solution is: 1901-05-22T22:20:13.81 UT1 1901-05-22T22:20:12.91 Terrestrial Time -0.907 seconds delta T +48°23'09.9" - 79°28'22.2" north lat, east lon So Paris astronomical time = 10:29:35 by my computation. Arago's value is 12 seconds later: 10:29:47. His estimated position is N48°23' W079°25', only a little different from my second computation. Unfortunately, the wrong time in my previous message spoiled your chronometer rate computation. So I'll do it again. March 2 occultation: 6:57:28 M (hack watch) 10:53:17 Tmp (my value) --------- -3:55:49 M-Tmp (hack watch error) 1:17:58 A-M (Arago's value) -3:55:49 M-Tmp (from above) --------- -2:37:51 A-Tmp (chron. error) May 22 lunar distance: 6:34:42 M (hack watch) 10:29:35 Tmp (my value) --------- -3:54:53 M-Tmp (hack watch error) 1:17:14 A-M (Arago's value) -3:54:53 M-Tmp (from above) --------- -2:37:39 A-Tmp (chron. error) clock rates: -3:55:49 M-Tmp (May 22) -3:54:53 M-Tmp (March 2) --------- -:56 Hack watch lost .69 s/day. -2:37:39 A-Tmp (May 22) -2:37:51 A-Tmp (March 2) --------- +:12 Chronometer gained .14 s/day. > And a last comment: while earlier running this example on my own, I was > a bit surprised at the "inaccuracy" of Arago's results, mainly due to > his Lunar coordinates surprisingly and significantly inaccurate by > to-day standards. It's interesting that the JPL ephemerides use no observations before the 20th century (I think the oldest are from 1911). --