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:
Thanks again for all the answers and explanations, I'm new in this, and only a
lover of Sundials and some astronomy. I saw all the Web sites you use and I
find very interesting, and very complex. I'll see if I can buy the book
Astronomical tables of the Sun, Moon and Planets, Jean Meeus, I
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
Alex
You say in your note But in mathematics uuuf, - but this is not
mathematics, it's astronomy! Nothing in the heavens moves with absolute
uniformity…..
If you want the very best astronomical calculations, then you must use the best
technology and that is provided free by NASA-JPL.
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
Also using Time Zone Master
1) Clicking any clock and going to the equinox page, you then click on
the equinox (5:05 EDT for my case - Ottawa)
2) Then go to the sidereal page it shows 9:12:28 GST (sidereal time)
3) The time difference to noon is 2h 57m 31s
Multiply x 15 - you get 44d 22m 45s E
Don't you hate it when you publish numbers with errors
I manually subtracted from noon incorrectly
3) The time difference to noon is actually 2h 47m 31s
Multiply by 15 gives 41d 52m 45s E
Open a new clock and enter the longitude, and equator
The result is near a town called Chisimayu in
This is my Subject;
Finding the position, Longitud, where, the sprig equinox, will ocurr at noon, I
found some diference between the results of The Dialist´s Companion, and Sun
v.5.6 Of R.Cernic, both programs I work for some time.
In Longitud 42°12,80 E at 13:03:42 PM it will be Noon,
Axel
Just a word of caution: The one thing that Dialist's Companion does NOT do
well at is determining the time of solstices and equinoxes. Please do not
use it as a standard for these times.
Fred Sawyer
2011/9/22 axel törnvall gonzalez atg...@hotmail.com
This is my Subject;
Finding the
My logic for answering the question of where on Earth will it be apparent noon at the instant of the autumnal equinox is:1. The Greenwich sidereal time at the time of the equinox (Julian day 2455827.87793)is 09:10:36.1 2. We want the longitude where the local sidereal time = 12:00:00 at this
Looking at our free windows programme - time zone master - it indicates
the autumn starts at 5:05 EDT
adding other clocks - Nairobi (and that whole timezone) turns out to
have the equinox at 12:05 EAT - (pretty close to noon)
its available from www.relativedata.com
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