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Nereid, the third largest of Neptune’s moons (mag. 18.69) and Minor Planet Christophe
#1
I managed to record the trail of Nereid, one of the fainter satellites of Neptune at mag. 18.69, according to SkyTools 4 Imaging.

Nereid is the third largest of Neptune’s moons, and the second to have been discovered. It was discovered on 1st May, 1949 by the Dutch American astronomer Gerard P. Kuiper (for whom the Kuiper Belt is named) using photographic plates from the McDonald Observatory in Fort Davis, Texas. It is named after the numerous daughters, called Nereids, of the sea god Nereus in Greek mythology.

Nereid has a diameter of about 340 km (210 miles). It revolves around Neptune with a period of just over 360 days in a highly elliptical orbit—the most eccentric of any known moon—that is inclined by more than 7° to the planet’s equator. Its mean distance from Neptune is 5,513,400 km (3,425,900 miles), which is about 15 times farther from Neptune than Triton. Nereid is exceedingly faint, making observations with even the largest Earth-based telescopes very difficult.

I took 60x30 sec frames then after a Meridian flip, another 50x60 sec frames. I threw these into PixInsight which handled the Meridian Flip and differing exposure times without breaking a sweat.

Images taken with a Tak Mewlon 210 F11.5, Tak Reducer/Flattener x0.8 and ZWO ASI 294 MM Pro camera from our back garden in suburban Brisbane, under Bortle class 6 skies on 5th Oct 2021.

I have overlaid Screen Captures from SkyTools 4 Imaging to show some of the field stars as well as the lucky catch of the Minor Planet (1698) Christophe at mag. 16.63 (Diameter: 10 - 31 km). Perihelion Distance is 2.8 AU, Aphelion Distance is 3.5 AU. I haven't updated the Minor Planet database for a few months and wonder if this has led to the slight discrepancy?


When I set the capture time in ST4, the plotted position of Christophe did not match the actual trail in my series of images. In ST4 it seems that Christophe was “behind” the recorded position by 2 or 3 hours? ST4 is set for my back garden location in Brisbane and the Win 10 PC clock was synchronised with the Time Server.

Cheers

Dennis


   

   

   
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#2
Amazing work! I love these puzzles. It would help greatly to know the UT of the image? AEST looks to be ahead of UT by 10 hours. Correct? I'm assuming you took the image after Astronomical Twilight, so 19:11 AEST when it would be high in the east. Or waited til it transited around 22:00 local. Best I can tell, south is up and east to the right. I suppose it is possible that orbital elements for Christophe have changed in 2 months but somehow I doubt it by several hours. I have the large rock at RA 23 28 29 DEC -4 40 30.1 at 22:19 local time 67° high due north using JPL elements with epoch date JD 2459396.5 (July 1, 2021). This places Christophe 12.3' WNW of Neptune. Did you try updating the asteroid elements within ST?

Just for grins, I used an element set from July 2021 that I had laying around and the position was off by ~16" in RA and 8' in DEC. This does seem to be close to the error shown in your image.

Looking again at the trail in your image of Christophe, it appears the image may have been taken between 14:53UT and 17:53UT, just eyeballing it.
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#3
I'd like to remind any casual readers of this thread that the position of a minor planet as calculated by SkyTools depends on the orbital elements used to plot the position, and any errors are not due to a fault in SkyTools itself, but to poorly determined, and often changing orbital elements as the asteroid passes close to the earth.
Clear skies,
Greg
Head Dude at Skyhound
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#4
(2021-10-07, 07:25 AM)Dennis Wrote: I have overlaid Screen Captures from SkyTools 4 Imaging to show some of the field stars as well as the lucky catch of the Minor Planet (1698) Christophe at mag. 16.63 (Diameter: 10 - 31 km). Perihelion Distance is 2.8 AU, Aphelion Distance is 3.5 AU. I haven't updated the Minor Planet database for a few months and wonder if this has led to the slight discrepancy?


When I set the capture time in ST4, the plotted position of Christophe did not match the actual trail in my series of images. In ST4 it seems that Christophe was “behind” the recorded position by 2 or 3 hours? ST4 is set for my back garden location in Brisbane and the Win 10 PC clock was synchronised with the Time Server.

Cheers

Dennis

Hello Dennis,

Nice image! I'm glad to see that Nereid is plotting in the correct position. Osculating elements are only truly accurate for about 40 days or so, and start to lose accuracy after that. So it is important to update your elements if you expect the positions to match closely, especially for asteroids near opposition, where the errors are magnified. Unfortunately, it's not as easy as it once was to obtain accurate and timely orbital elements. The Minor Planet Center has slowly been making changes that has degraded the accuracy of elements, especially for minor planets that do not pass close to the earth. Unfortunately one could write a book on this subject! But there are ways to obtain more up to date elements. For starters I suggest using ASTORB to obtain your elements, and filtering so that you don't add hundreds of thousands of very faint asteroids.
Clear skies,
Greg
Head Dude at Skyhound
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#5
Hi Dennis,

Spectacular image! Nice catch. Here's what my ST4v shows for the old iTelescope observing site at Bathhurst: [attachment=2030]

Bathhurst is 33° 24'S 149° 30'E, so near Sydney.

The time is 2354 on 2021 Oct 5. My elements for Christophe are for epoch 2021 Jul 5. ST4v estimates Christophe's motion at 25.4"/hr.

Phil S.
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#6
So his plot/trail of Christophe is danged close.

And the fact that his plot in ST is off only indicates the elements were not up to date as Technoking mentioned.

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#7
Very nice capture, Dennis, thanks for posting it!
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#8
(2021-10-07, 01:29 PM)bigmasterdrago Wrote: Amazing work! I love these puzzles. It would help greatly to know the UT of the image? AEST looks to be ahead of UT by 10 hours. Correct? I'm assuming you took the image after Astronomical Twilight, so 19:11 AEST when it would be high in the east. Or waited til it transited around 22:00 local. Best I can tell, south is up and east to the right. I suppose it is possible that orbital elements for Christophe have changed in 2 months but somehow I doubt it by several hours. I have the large rock at RA 23 28 29 DEC -4 40 30.1 at 22:19 local time 67° high due north using JPL elements with epoch date JD 2459396.5 (July 1, 2021). This places Christophe 12.3' WNW of Neptune. Did you try updating the asteroid elements within ST?

Just for grins, I used an element set from July 2021 that I had laying around and the position was off by ~16" in RA and 8' in DEC. This does seem to be close to the error shown in your image.

Looking again at the trail in your image of Christophe, it appears the image may have been taken between 14:53UT and 17:53UT, just eyeballing it.

Whoops - I keep falling into the trap of thinking that the exposure details are recorded within the JPG file like the EXIF data in my Canon camera. Rolleyes

Here are the details for Sunday Oct 3rd Brisbane:

30 Sec Frames (x60)
9:39 to 10:35pm AEST (UT+10)
11:39:00 UTC to 12:35:00 UTC

Meridian Flip

60 secs Frames (x50)
10:39 to 11:54 AEST (UT+10)
12:39:00 UTC to 13:54:00 UTC

Latitude: 27° 31’ 28” = 27.5243
Longitude: 153° 03’ 40” = 153.0611
Elevation: 30m

Cheers

Dennis

(2021-10-07, 03:29 PM)theskyhound Wrote: I'd like to remind any casual readers of this thread that the position of a minor planet as calculated by SkyTools depends on the orbital elements used to plot the position, and any errors are not due to a fault in SkyTools itself, but to poorly determined, and often changing orbital elements as the asteroid passes close to the earth.

Thanks for expanding on this issue Greg, I have found SkyTools to be very reliable and accurate, although I am oblivious to what magic goes on under the hood. Smile 

Cheers

Dennis

(2021-10-07, 03:42 PM)PMSchu Wrote: Hi Dennis,

Spectacular image! Nice catch. Here's what my ST4v shows for the old iTelescope observing site at Bathhurst: 

Bathhurst is 33° 24'S 149° 30'E, so near Sydney.

The time is 2354 on 2021 Oct 5. My elements for Christophe are for epoch 2021 Jul 5. ST4v estimates Christophe's motion at 25.4"/hr.

Phil S.

Wow - thanks Phil, so many Minor Planets - I'll have to go back and look at my image and try and match the field and identify them. Smile 

Cheers

Dennis
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#9
Hi Dennis,

It looks like you recorded your exposures around midnight on Oct 3, but the ST4v chart that I posted was for Oct 5 23:54, two days later.  Here's the predicted motion from Oct 3-6: [attachment=2036]

Again from the Bathhurst Observatory. I need to add the location that you posted for the future.

Have you uploaded your image to Astrometr.net? They can plate solve it & ID the MPs detected. I've used it to platesolve some images taken with iTelescopes.

Here's a link to the web based site:

Astrometry.net

Good luck,

Phil S.
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#10
ASTAP also plate solves and annotates asteroids (everything done locally), see a demo at https://www.youtube.com/watch?v=oTRzlNlpY7w.
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