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Strange jumps of Pluto between 2246 and 2247B (fwd)

 

Hi,

If i am not mistaken there is a confusion in the new code between elements reference epoch and perihelion epoch. Plus, daily motion truncated to 2 significant digits is probably too
harsh.

2447654.529 for the perihelion brings it back in the ballpark,
and n=0.00395 seems to be closing quite well. Is n available
with more accuracy in the Almanach ?

--
fm

On Mon, 24 Jan 2022, Brandon Rhodes wrote:

On Mon, Jan 24, 2022 at 2:27 PM Brandon Rhodes via groups.io
<brandon@...> wrote:
On Mon, Jan 24, 2022 at 2:06 PM Elwood Downey <elwood.downey@...> wrote:
1. I confirm your report using XEphem 4.0.1 but I can also report
the?jumping does NOT happen with my legacy 3.7.6 so?SOMEBODY BROKE
SOMETHING.
Back in July, someone offered to update the Pluto orbital elements … Here's the code
update they suggested:

I have just tested and can confirm that the above-linked commit is the one that introduced
the discontinuity. Apparently this new elliptical orbit for Pluto does not provide a smooth
join with the “chap95_pluto” Pluto positions that "planpos()" uses over the time period
from?CHAP_BEGIN to?CHAP_END which, it appears, are the dates?1689/3/19 through?2247/10/1.
I'm open to ideas about the best way to resolve this. Should we revert the improvement and go
back to our old Pluto ellipse?
_._,_._,_
 

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Ouuups ... I think you are on the good way !
Reference done from my early troubles of Chebichev coeff of planets 2020-2040 :

All the format aspect (columns, width, precision, spaces, NO tabs ...) must be identical !
... or you'll get problems.

Best regards,
Serge

On 25/01/2022 12:35, dulle wrote:
Hi,

If i am not mistaken there is a confusion in the new code between elements reference epoch and perihelion epoch. Plus, daily motion truncated to 2 significant digits is probably too
harsh.

2447654.529 for the perihelion brings it back in the ballpark,
and n=0.00395 seems to be closing quite well. Is n available
with more accuracy in the Almanach ? 

-- 
Serge Montagnac + GPG Key 0xDF083D7B + 
    Nature, Not Human Activity, Rules the Climate.

 

On Tue, Jan 25, 2022 at 1:01 PM Serge Montagnac <obs.psr@...> wrote:
All the format aspect (columns, width, precision, spaces, NO tabs ...) must be identical !
... or you'll get problems.

Happily, these elements sit in the raw C code, which is impervious to any whitespace sensitivity. So they should not be haunted by any format problems.

I am reverting the recent?commit and restoring Pluto to its previous long-term orbit! I'll see about a new release in the next few days to make it official.
 

Hi,

Attached are 2 plots of the same trail, one with the old elements,
one with the new fixed ones (ie perihelion epoch, and n)


diff --git a/libastro/plans.c b/libastro/plans.c
index 9680c2a..805d88f 100644
--- a/libastro/plans.c
+++ b/libastro/plans.c
@@ -53,9 +53,10 @@ double *ret) /* ecliptic coordinates {l,b,r} at equinox of date */
inc0 = 17.097, /* inclination, deg */
Om0 = 110.297, /* long asc node, deg */
omeg0 = 115.058, /* arg of perihel, deg */
- mjp = 2459000.5 - MJD0, /* epoch of perihel */
+ mjp = 2447654.5 - MJD0, /* epoch of perihel */
mjeq = J2000, /* equinox of elements */
- n = 0.0039; /* daily motion, deg */
+ n = 0.003959; /* daily motion, deg */

double inc, Om, omeg; /* orbital elements at epoch of date */
double ma, ea, nu; /* mean, excentric and true anomaly */
[

The new ones give better continuity with Chapront's solution, which does not mean accuracy. If anyone needs better accuracy over centuries, a simple ellipse will probably not make it. So as continuity with Chapront is ensured, I think we can easily fix and keep the new elements.
--
fm

On Thu, 27 Jan 2022, Brandon Rhodes wrote:

On Tue, Jan 25, 2022 at 1:01 PM Serge Montagnac <obs.psr@...> wrote:
All the format aspect (columns, width, precision, spaces, NO tabs ...) must be
identical !
... or you'll get problems.
Happily, these elements sit in the raw C code, which is impervious to any whitespace
sensitivity. So they should not be haunted by any format problems.
I am reverting the recent?commit and restoring Pluto to its previous long-term orbit! I'll
see about a new release in the next few days to make it official.
--
Dr Fran?ois Meyer Tel : (+33) 3 81 66 69 27 Mob : (+33) 6 27 28 56 83
Dir. exécutif plateforme OscIMP
Dir. LNE-LTFB, laboratoire temps-fréquence associé au LNE
Institut UTINAM / OSU Theta
41b avenue de l'Observatoire, BP1615
25010 Besancon cedex - FRANCE
** Universite de Franche-Comte ** CNRS UMR 6213 ** URA 3245

xephem-pluto-old.png
xephem-pluto-new.png

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