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PostPosted: Sat, 23-04-16, 13:55 GMT 
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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
Quote:
In predicting the precise times of topocentric phenomena, like solar eclipse contacts, both TT
and UT1 come into play. Therefore, assumptions have to be made about the value of ∆T at the
time of the phenomenon. Alternatively, the circumstances of such phenomena can be expressed
in terms of an imaginary system of geographic meridians that rotate uniformly about the Earth’s
axis (∆T is assumed zero, so that UT1=TT) rather than with the real Earth; the real value of ∆T then does not need to be known when the predictions are made. The zero-longitude meridian of
the uniformly rotating system is called the ephemeris meridian. As the time of the phenomenon
approaches and the value of ∆T can be estimated with some confidence, the predictions can be
related to the real Earth: the uniformly rotating system is 1.002738 ∆T east of the real system
of geographic meridians. (The 1.002738 factor converts a UT1 interval to the equivalent Earth
Rotation Angle — i.e., the sidereal/solar time ratio.)


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. :rool: 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).

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PostPosted: Sat, 23-04-16, 14:09 GMT 
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Quote:
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

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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PostPosted: Sat, 23-04-16, 14:35 GMT 
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Hope the astronomers will remove UTC from the universe, definitely... :twisted:

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PostPosted: Sun, 24-04-16, 8:52 GMT 
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...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)]
Attachment:
pluto_charon.jpg
pluto_charon.jpg [ 270.29 KiB | Viewed 1613 times ]

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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PostPosted: Sun, 24-04-16, 23:08 GMT 
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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? :°

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PostPosted: Mon, 25-04-16, 6:50 GMT 
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fenerit wrote:
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? :°

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?

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PostPosted: Mon, 25-04-16, 13:14 GMT 
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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.
Attachment:
horiz_grid_displ_vsop87.jpg
horiz_grid_displ_vsop87.jpg [ 202.14 KiB | Viewed 1586 times ]

Attachment:
jpl_saturn_altaz.png
jpl_saturn_altaz.png [ 44.83 KiB | Viewed 1586 times ]

Attachment:
horiz_grid_displ_spice.jpg
horiz_grid_displ_spice.jpg [ 202.61 KiB | Viewed 1586 times ]

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.

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PostPosted: Mon, 25-04-16, 15:33 GMT 
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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

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PostPosted: Mon, 25-04-16, 16:04 GMT 
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Nope, doesn't seem to work, same issue. My SpiceRotation for the Earth is:

Code:
SpiceRotation
{
Kernel [ "pck00010.tpc" "earth_latest_high_prec.bpc" "naif0010.tls" "earth_fixed.tf"]
Frame "EARTH_FIXED"
}

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PostPosted: Tue, 10-05-16, 19:33 GMT 
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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?)]
Attachment:
1ECL2_2003_3_13.jpg
1ECL2_2003_3_13.jpg [ 114.43 KiB | Viewed 1478 times ]


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?)]
Attachment:
2O1_2014_12_20.jpg
2O1_2014_12_20.jpg [ 98.73 KiB | Viewed 1478 times ]


Altogether, the orbit accuracy is impressive!
Enjoy,

Fridger

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PostPosted: Tue, 17-05-16, 23:02 GMT 
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Indeed impressive. :clap:

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PostPosted: Wed, 18-05-16, 8:04 GMT 
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abramson wrote:
Indeed impressive. :clap:


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!

Attachment:
b.jpg
b.jpg [ 34.63 KiB | Viewed 1421 times ]

Cheers
F.

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PostPosted: Wed, 18-05-16, 14:34 GMT 
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Oh, man, such a pitty it's clouded. ;)

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