These things makes me crazy. Let suppose that:
UT1-UTC = -0.2s (now)
DeltaT = 32.184 + 36 - (-0.2) = 68.4s (now) while for Espenak-Meeus is 69.6s

Then I read page 11 of :
http://aa.usno.navy.mil/publications/docs/Circular_179.pdf


Hence I do: 1.002738 * DeltaT = 68.6s that is a value for which the latest -1 leap second that subtracted from Espenak-Meeus get the same value: 69.6 - 1 = 68.6s. So my question is: is correct to do so or it is just a coincidence? I cannot test the systemtime neither onward nor backwards because it is fixed at "now" but these values should be the same also in simulation (harking back from internal TDB to UTC).

_________________
Never at rest.
Massimo

While not being a great expert in these "finesse" issues about time, I would guess that deviations around 1 second could well be due to using the LINEAR approximations above!

Fridger

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Hope the astronomers will remove UTC from the universe, definitely...

_________________
Never at rest.
Massimo

...and NOW --after JohnVV linked-in the latest spice kernel update (plu043.bsp -> plu055.bsp) viewtopic.php?f=18&t=599#p13825
-- it's time for checking the Pluto-Charon mutual eclipses!

Hello....

[click first on picture and then hit your browsers fullscreen key (F11 for FF)]

The "Big Brothers" (1920 x 1080) are waiting ...
and thus it's time to stay tuned in my new respective thread
viewtopic.php?f=11&t=823

Fridger

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Ahem... neither to be a ***beeeep*** nor to find "the hair within the egg", but how are going the things in celestia.Sci about the displacement of the horizontal grid with SPICE?

_________________
Never at rest.
Massimo

No idea, since I had no time yet to test that. Can you describe a configuration precisely where and how the displacement happens with Celestia?

Fridger

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This is Saturn from Rome at 2016-Apr-26 00:00. All the objects have the same issue. The first image show the horizontal grid in VSOP87, the second the azimuth and elevation from JPL HORIZONS and the third the horizonta grid in SPICE, respectively. Alt-Az are topocentric refracted.



The grid is not where it should be.
Note: do not use the current version of the plugin to check altitude; that is a more enhanced new version not yet released.

_________________
Never at rest.
Massimo

still on my first cup of Coffee so...

i can look at the earth "earth_latest_high_prec.bpc" with the "earth_fixed.tf"
ftp://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/
and see if that solves it

_________________
"I don't pitch Linux to my friends, I let Microsoft do that for me."
Using OpenSUSE 42.1 & Scientific Linux 6.7

Nope, doesn't seem to work, same issue. My SpiceRotation for the Earth is:

_________________
Never at rest.
Massimo

Hi all,

meanwhile, I further simplified quite significantly the code along with the procedure of investigating mutual (Galilean) events. Only the earth-bound date-time of an event (UTC) needs to be entered into celestia.Sci's Time dialog, the rest proceeds automatically.

Let me show you for the previously addressed two events how well they match the respective predictions.

1) 1ECL2_2003_3_13.jpg
++++++++++++++++++++
In this event the shadow of Io is partially cast onto Europa. The event happened in March 13 of 2003 with a maximum around 23h 05m.

[Click on image for a bigger size and then hit your browser's fullscreen key (F11?)]


On the r.h.s you also see the filled-in Time dialog for this example. Note that the Time dialog is opened by simply clicking onto the 1st tool-button in the lower left of the canvas! Very handy...The eclipse event happend just a few minutes before Europa vanishes behind Jupiter, a small part of which you can see on the right...

Dr. Arlot's predicted time (TT=TerestialTime) for the maximum of the event is visible in the simulation settings, and indeed the display verifies the perfect agreement!
Couldn't be better...

2) 2O1_2014_12_20.jpg
+++++++++++++++++++
Here Europa occults Io partially . The predicted maximum is at 05h:36m in perfect agreement with the celestia.Sci simulation!

Here is the corresponding screenshot! This time the Time dialog is dogged into the main canvas on the right. Just to illustrate a few of the many possibilities...

[Click on image for a bigger size and then hit your browser's fullscreen key (F11?)]


Altogether, the orbit accuracy is impressive!
Enjoy,

Fridger

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Indeed impressive.

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Guillermo Abramson
Bariloche, Argentina

Well there are many more challenging tests along these lines:

After the Jovian system, the focus relies on Pluto-Charon mutual events and most recently: Observed Transits of the EXO planets b , c and d across their star Trappist-1! (Using Andrew's orbit data). viewtopic.php?f=17&t=828#p13862

The latter checks are particularly fun, since the distance amounts to 39.466 ly.
Hence celestia.Sci (Celestia) predictions of the transit of EXO b, for example, test a lightTravelDelay of 14415.03 days for EXO b, the orbital period of which is only 1.51085 days!

In other words: an event having taken place in Nov 29 1976 within the Trappist-1 system would be observed on Earth today!


Cheers
F.

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Oh, man, such a pitty it's clouded.

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Guillermo Abramson
Bariloche, Argentina