Gian:
I'm becoming convinced that the use of the simpler nutation model is the
culprit. I did a detailed analysis of a case where the difference between
Meuus and my result is 1 second, and it turns out that the simpler nutation
model differs from the more complex one by an amount that accounts
Brad,
Are you sure you are using the full VSOP87 theory? I don't think it has
been published in print form, anywhere. The appendix in Jean Meeus's
Astronomical Algorithms gives an abridged form of VSOP87, and this could
explain your discrepancies with Table 27.E.
Roger
On Thu,
Roger:
I'm pretty sure I am using the full theory. I'm definitely not using the
abridged form from Meuus's Appendix.
The full version is available from an FTP server. But I found (I confess I
don't remember where) an ASCII text file that, based on a more than cursory
examination, seems to be an
Sincere apologies to Mr Meeus, whose last name I've been misspelling. His
book (Astronomical Algorithms) has been a revelation about how to write
about applied mathematical astronomy.
With deepest respect, Brad
On Fri, Sep 30, 2011 at 8:24 AM, Brad Lufkin bradley.luf...@gmail.comwrote:
Roger:
Ø The full version is available from. . .
Brad,
So it is! Thanks very much for letting me know about this.
But VSOP87 is about of the same vintage as the older JPL ephemeris DE200,
about 25 years ago. JPL is now up to DE421, and calculations consistent
with DE421 are available from
Roger:
Blast!
My program predicts the time as 2012 Mar 20 05:15:3*3* DT, not 05:15:3*2*.
All kidding aside: as I said in a previous post, I think the difference is
that I'm using a too-simple nutation model.
I hope I haven't strained the patience of those sundialists whose interests
don't extend
Brad, I did not have enough time to go through my code but I could see that I'm
using the simpler nutation algorithm too.
So I guess you are probably right.
Hope to have more time in the week end.
Ciao.
Gian
Messaggio originale
Da: bradley.luf...@gmail.com
Data: 30/09/2011 12.59
A:
Hi Brad, good news !
I have introduced the complete nutation computation but also corrected a bug
that I have found in the code.
Each one was contributing with some seconds to the total error.
Now in OS all the results are exactely the same as in Meeus book, also
equinoxes and solstices
Gian:
Continuing my investigation, I tried to reproduce Table 27.E of Meuus's
Astro Algorithms, 2nd Edition. The table shows the time, to the nearest
second, of the solstices and equinoxes for the years 1996-2005. The table is
based on the full VSOP87 theory.
I too am using the full theory, along
Many thanks Brad, that really makes me feel better !
I will let you know the results of my analysis.
Ciao.
Gian
Messaggio originale
Da: bradley.luf...@gmail.com
Data: 28/09/2011 3.58
A: sun.di...@libero.itsun.di...@libero.it
Cc: Sundial Mailing Listsundial@uni-koeln.de
Ogg: Re: Re:
Axel,
from Astronomical tables of the Sun, Moon and Planets, Jean Meeus, second
edition, page 151: Semptember equinox in 2011 is on day 23rd at 9:05:44
(Dinamical Time). To convert to Universal Time one must subtract the value of
DeltaT.
Orologi Solari considers a value of DeltaT = 67.5 so
Gian et al:
I need to take back my last statement: it turns out that VSOP is accurate to
about 10**(-6) degrees.
Brad
On Tue, Sep 27, 2011 at 5:36 AM, Brad Lufkin bradley.luf...@gmail.comwrote:
Gian:
it's likely that the difference between your result and the result in Meuus
is due to (a) the
Just for clarity:
http://aa.usno.navy.mil/data/docs/EarthSeasons.php shows the following
UT values:
20112011
Perihelion Jan 3 19Equinoxes Mar 20 23 21Sept 23 09 05
AphelionJuly 4 15Solstices June 21 17 16Dec 22 05 30
ie: 9:05 UT
from
Brad,
sun parameters are computed by OS using the VSOP87 theory as for Meeus results.
Aberration and nutation are taken into account (or they should be, this is one
of the points I have to check).
I did not interpolate but just manually changed the simulation time in order to
get 180.0
Gian:
I calculated the longitude using VSOP87D and all the corrections mentioned
in Meuus's Astro Algorithms and, if it makes you feel any better, my result
agrees with yours (i.e., the Sun's longitude is closest to 180 degrees at
9:05:41 DT).
Brad
On Tue, Sep 27, 2011 at 2:22 PM,
Here is my answer to Axel's question.
With Orologi Solari in simulation mode, looking for the time of sun longitude
= 180 degrees, I find:
my time (TMEC + DST) = 11:04:33 that corresponds to GMT 9:04:33.
At that time sun is on the local meridian of a place with longitude = (12:00:00
-
Thanks for your answers, and for you Fabio that personally wrote to my mail,
We all arrived at different results, but the differences are minute
in longitude and with a circumference of the earth at latitude 0 °, (Equator)
of which is 40.075,036 kilometers, every minute of that difference is
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