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Old 02-09-2019, 04:03 PM
Dennis
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Nereid (18.69m), third largest of Neptune’s moons – Brisbane 1st Sept 2019

Inspired by Marc’s heroic 2650 mm focal length images of M8 and M20, I decided to try a little long FL imaging myself, but at a much more modest 1932mm. With Neptune making an evening appearance, I thought that Nereid, discovered in 1949, would make a good target. I recently purchased a copy of SkyTools 4 Imaging, as with this major release, the author has added several new and interesting objects such as Nereid.

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.

Almost everything we know about Nereid comes from the images taken by Voyager 2 in 1989; its closest approach was approximately 4.7 million km.

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.

Nereid’s highly eccentric orbit (eccentricity 0.75, the highest of any solar system moon) takes it from 1.37 million km from Neptune to 9.66 million km (average 5.51 million km); unlike Triton, and like the other inner moons, Nereid’s orbit is prograde. This suggests that it may be a captured Kuiper Belt object, or that its orbit was substantially perturbed when Triton was captured.

The attached images were taken using a Tak Mewlon 210, Tak x0.8 Reducer/Flattener and an SBIG ST2000XM camera. I captured 30x300 sec frames on 1st Sept 2019. I had to discard some of the early frames where Nereid was at less than 45 degrees altitude, due to the smearing effects of the atmosphere. The faint dot of Nereid tightened and became more obvious as the object approached the meridian. Images were calibrated, aligned and stacked using CCDStack2 and finished in PS CS. I blended in a single 300 sec regions showing Neptune and Triton as the movement over the frames blew this region out.

I have overlayed skycharts from SkyTools 4 and The Sky X Pro to identify some of the other objects in the field. I have also included a DSS image (colour) from Astrometry.Net showing the field - wish I had their telescopes...

In 2001, two surveys using large ground-based telescopes – the Cerro Tololo Inter-American Observatory and the Canada-France-Hawaii telescopes – found five additional outer moons bringing the total to thirteen. Follow-up surveys by two teams in 2002 and 2003 respectively re-observed all five of these moons – which were Halimede, Sao, Psamathe, Laomedeia, and Neso.

And then on July 15th, 2013, a team of astronomers led by Mark R. Showalter of the SETI Institute revealed that they had discovered a previously unknown fourteenth moon in images taken by the Hubble Space Telescope from 2004–2009. The as yet unnamed fourteenth moon, currently identified as S/2004 N 1, is thought to measure no more than 16–20 km in diameter.

Image centre: RA 23h 15m 06.957s: DEC -05° 57' 39.306"
FOV: 12.7 x 9.55 arcmin
Image Scale: 0.746 arcsec/pixel

Nereid
Magnitude: 18.69
PA: 62.7 deg
Separation: 455.1”
Earth Distance: 28.9 AU

Cheers

Dennis
Attached Thumbnails
Click for full-size image (Nereid.jpg)
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Click for full-size image (Nereid Inverted.jpg)
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Click for full-size image (Nereid Text.jpg)
110.4 KB117 views
Click for full-size image (Nereid ST4 Overlay Crop 1024.jpg)
101.4 KB105 views
Click for full-size image (Nereid The Sky X Pro Overlay Crop 1024.jpg)
180.2 KB103 views
Click for full-size image (DSS.jpg)
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Old 02-09-2019, 06:39 PM
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theodog (Jeff)
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Nice image.
Good background info.
Well done Dennis.
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Old 03-09-2019, 10:11 AM
inline_online (Dan)
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Very interesting read and great pics.
Nice to see boundaries being pushed.
Well done
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Old 03-09-2019, 04:07 PM
Dennis
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Quote:
Originally Posted by theodog View Post
Nice image.
Good background info.
Well done Dennis.
Quote:
Originally Posted by inline_online View Post
Very interesting read and great pics.
Nice to see boundaries being pushed.
Well done
Thanks Jeff and inline_online, I appreciate your comments.

Neptune is at conjunction on 9th Sept, so I thought I'd have a go at Nereid whilst it is so close to us.

Cheers

Dennis
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Old 03-09-2019, 06:43 PM
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That's a great challenge Dennis, never really thought of this moon as imagable. Great write up.

John.
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Old 03-09-2019, 06:58 PM
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Top stuff as usual Dennis. Thanks for sharing another great project.
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Old 04-09-2019, 07:21 AM
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Nice write up and great pics to illustrate. Top shelf.
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Old 04-09-2019, 08:07 AM
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Very cool images Dennis.
I never even imagined capturing this object would be possible with amateur equipment.
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Old 04-09-2019, 03:29 PM
Dennis
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Thanks for all the comments and feedback folks, I appreciate them.

Just to ensure that I hadn't recorded a random clump of grains of light masquerading as Nereid, I stepped outside again 2 nights later and took another series of images with the same gear and Nereid appeared where it was predicted to be.

I'm glad that this far off satellite of Neptune wasn't motoring along any faster, as its photons may then not have accumulated enough to record its trail.

Here is an inverted image composite showing the movement of Neptune, Triton and Nereid between 1st and 3rd Sept.

I have done a copy/paste of Neptune/Triton from a single frame from the middle of each series, to overlay the smeared trails due to their real-time movement across the frames in the final aligned/stacked images.

Cheers

Dennis
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Old 04-09-2019, 03:34 PM
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That montage is uber cool.
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Old 04-09-2019, 07:41 PM
Dennis
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Using CCDStack I just opened the 20x300 sec frames from 01 Sept and the 24x300 sec frames from 03 Sept and performed the Align and Stack functions, with Combine set to Maximum, to discover I had also registered a couple of longer, faint trails located below Neptune and Nereid.

This is the “Raw” image output from CCDStack, (annotated in PS CC), so you can see the overlap artefact between the 01 and 03 Sept data sets, along with the two faint trails.

The left-hand trail is that of NEO 2001 TQ44, a Main Belt Object class Asteroid at R.A.: 23h14m47.8s Dec.: -05°53'09" (2000) in Aquarius with a Magnitude: 18.81.

The right-hand trail is that of 2003 QA35, an Outer Main Belt Object class Asteroid at R.A.: 23h15m27.1s Dec.: -05°51'29" (2000) in Aquarius with a Magnitude: 18.36.

I used SkyTools 3 Pro to identify the Asteroids and obtain the detailed information.

It looks like these images sets are the unexpected gifts that keep on giving.

Cheers

Dennis
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Old 05-09-2019, 07:03 AM
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Great detective work Dennis. I assume you don't do any data rejection at all on those stacks. Correct?
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Old 05-09-2019, 09:01 AM
Dennis
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Great detective work Dennis. I assume you don't do any data rejection at all on those stacks. Correct?

Hi Marc

I use CCDStack2 and this is my workflow:
  • Calibrate using Darks and Flats
  • Run the Hot Pixel and Interpolate commands at their default settings.
  • Register
  • Normalise
  • Stack.

In these images (normal view), I have noticed that I have several small black holes scattered around the frame which appear less obvious when using SUM, but become more prominent when using MEAN or MEDIAN combine.

I should really re-visit the CCDStack Tutorial I purchased some while ago, as it has been several years since I last looked at these.

Cheers

Dennis
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Old 07-09-2019, 02:20 PM
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Nice work Dennis! It's fun chasing the less-explored chips of ice in the Solar System
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Old 07-09-2019, 11:13 PM
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Wow. Amazing capture.
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Old 08-09-2019, 05:32 PM
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Impressive Dennis and always good to see Astronomy in the urban environment.
Derek
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Old 11-09-2019, 08:44 AM
Dennis
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Thank you Andy, Kevin and Derek, I appreciate your comments.

I had a little play with the data and managed to overlay, albeit crudely, the Neptune and Triton pairs over the grossly exposed stacks.

I also copied the FOV from SkyTools 4 Imaging which nicely identifies the Asteroids.

Cheers

Dennis
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Old 11-09-2019, 09:05 AM
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That last montage is a great record of all the bits and pieces over the time period. One to frame.
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Old 11-09-2019, 05:33 PM
Dennis
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That last montage is a great record of all the bits and pieces over the time period. One to frame.
Thanks Marc - next time I'll try to align the fields for both imaging sessions, to avoid the offset overlap.

Cheers

Dennis
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Old 12-09-2019, 03:24 PM
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Late to comment, but have been following this thread from the beginning. As usual, meticulous and detailed images and posts, mate. Awesome work.
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