Neptunian System Imaging Options

[machi]

Neptune from Voyager 2. Color is from images with CH4JS, green and orange filter.
Shadows of three moons are visible.
Second image is with possible interpretation.

Attached thumbnail(s)

 

[Stu]

Yes!!! I was hoping you'd focus your imaging magic towards Neptune!

[machi]

It was only matter of time.

[tedstryk]

Beautiful! I have also worked with these images and interpreted the moon you considered Galatea to be Naiad, but other than that I agree with your interpretation.
Edit: One other question: Which color did you use the CH4JS filter for? It is even redder than the orange filter, but from your listing order it seems like you used it as blue.

[machi]

CH4JS (with reduced contrast) was used as red color. Another ones: Orange -> green, green -> blue.
So this is false color, but corrected to approximately true color.

[tedstryk]

That makes good sense. I interpreted too much from the order you listed the filters.

[Ian R]

Aaaahh... Neptune! I recall taping any mention of the Voyager 2 flyby on TV as a rather eager seven year-old.

Great picture Daniel.

[nprev]

...wow!

[Stu]

Just so you know Machi, that new image will make its Outreach debut tonight, here in Kendal, in a talk being given to the 10th Kendal Cubs! (all ten of them!)

[Ian R]

Are these the famous shadow-casting cirrus clouds, I wonder?

[ngunn]

I can't help noticing similarity between clouds on Titan and the ones in that Voyager view of Neptune. In particular the biggest Neptune cloud with its north-south branch does resemble somewhat the big cloud recently seen on Titan. In general, and in both cases, the clouds cover only a small fraction of the globe and are predominantly in the form of long east-west streaks. Of course so much else about the two worlds is so very different. I have no idea whether the morphological similarity signifies anything interesting.

[machi]

I'm not expert about clouds, so I don't know exactly if it's cirrus, but these are real clouds encircling Neptune's pole.
One of my future image will show this region with higher resolution.

[machi]

Neptune with cirrus clouds swirling around south pole.
Slightly differences in color are caused by different kinds of filtered images (CH4JS, clear, violet and CH4JS, orange, clear).

Attached thumbnail(s)

 

[antipode]

Really enjoying this thread Machi.

At the time these images were first released I'd been backpacking through Europe for months and had totally forgotten about the Voyager Neptune encounter. One day on the streets of Paris I saw this incredible blue disk staring back at me from a news stand. I remember just standing there staring at it for ages - I just couldn't believe how compelling and unexpected all that atmospheric structure was!

Now - back to that last image. Can I see a small bright/dark vortex thingy at the pole? Might we be looking at a miniature version of Saturn's 'evil eye'?

P

p

[machi]

"Really enjoying this thread"

I am glad to hear that.

"Can I see a small bright/dark vortex thingy at the pole? Might we be looking at a miniature version of Saturn's 'evil eye'?"

Maybe this little animation (1 frame = 5sec real time) give answer:

Attached File(s)

 NSP25f5s.avi ( 915.82K ) Number of downloads: 2417

 

[nprev]

Wow, that animation's smooth; had to look hard twice to see that the white clouds were really moving. Nice!!!

[Astro0]

Stop that Machi. You're making my eyes hurt
Brilliant.

[Juramike]

Wow! That was neat! It gave the impression of just sitting there watching Neptune silently rotate underneath.

[brellis]

That is so relaxing to watch! Amazing work machi

[sgendreau]

Holy smokes, machi -- that's gorgeous.

[ElkGroveDan]

That slow motion beauty could make it the opening scene for Stanley Kubrick's grandson's film 2041 A Space Iliad.

[nprev]

Yeah, there's definitely something @ the South Pole...can't tell if it's an innie or an outie, though.

[machi]

Thanks!

Every planet, especially planets with atmosphere, looks so majestic from close.

"Yeah, there's definitely something @ the South Pole...can't tell if it's an innie or an outie, though."

I see central eye of the south pole "hurricane" and three clouds in him. One cloud is prominent, two clouds are nearly invisible.
I have somewhere article in which authors directly measured wind speed at south pole, perhaps using these clouds.

[machi]

Partial mosaic of Neptune. Four NAC images over WAC image.
Color from CH4JS, CH4U and violet WAC images.

Attached thumbnail(s)

 

[machi]

Another partial mosaic of Neptune. Now at resolution 10.5 km/pix.
Color is added from global images (as uniform color).

Attached thumbnail(s)

 

[machi]

Small (10s of km) bright clouds over Neptunian South Pole Region. Narrow angle camera (NAC) image has resolution around 7.4 km/pix.
Details are extremely enhanced (in NAC image), but color (from violet and green wide angle camera images) is very decent.
Subtle shadows under two small clouds are visible.

[MarcF]

Not really new, but a nice article about Neptune spin time !

http://io9.com/5817732/scientists-calculat...tunes-spin-time

[tanjent]

The article uses the puzzling phrase "we thought we knew" to suggest that the radio-based measures of the big planets are somehow invalid, but does not explain why any combination of atmospheric features, observed for any length of time, should give a better estimate of the rotation time of the planetary core. He makes a convincing case that different atmospheric strata, at different latitudes, rotate at different speeds. It is remarkable that he finds as much consistency among multiple features as he does, but why should these supplant the radio-based measures?

[MarcF]

Some more informations can be found here:

http://uanews.org/node/40494

"So based on those radio signals, we thought we knew the rotation periods of those planets"
But when the Cassini probe arrived at Saturn 15 years later, its sensors detected its radio period had changed by about 1 percent. Karkoschka explained that because of its large mass, it was impossible for Saturn to incur that much change in its rotation over such a short time...

Even more puzzling was Cassini's later discovery that Saturn's northern and southern hemispheres appear to be rotating at different speeds.
"That's when we realized the magnetic field is not like clockwork but slipping," Karkoschka said. "The interior is rotating and drags the magnetic field along, but because of the solar wind or other, unknown influences, the magnetic field cannot keep up with respect to the planet's core and lags behind."

[tanjent]

Hey thanks MarcF. That sounds like a clear reason to reject the radio signal-based measure. Earth's field also meanders around and it originates in the liquid regions of the interior IIRC, so no reason to think it works differently on other planets. But I still have to doubt that any number of observations of the visible atmospheric strata are likely to conclusively match Neptune's core rate. Maybe that doesn't matter as long as you have something stable to point to. (At Saturn I suppose it might be harder to find a stable constellation of spots to observe because the seasonal broadening and narrowing of the ring shadows probably influences the rotation rate by thermally by inducing changes in the radius.)

[MarcF]

I found even a nicer movie:
http://www.youtube.com/watch?v=_BPY1aGsrPs
Best regards,
Marc.

[Paolo]

New Neptunian moon discovered
http://www.skyandtelescope.com/news/home/N...-215535121.html
I was wondering: being so close to the planet, any chances that it was already present in Voyager imagery?

[Explorer1]

The article says the discoverer couldn't find it in them.

[Paolo]

The article says the discoverer couldn't find it in them.

they seem to have updated it since I posted my comment...

[elakdawalla]

I had the same question and asked Mark. He replied:

I did extrapolate the orbit back to the Voyager era and search the images that were supposed to have captured it. Apparently it is just too small for the Voyager cameras. I seem to recall that their quoted detection limit was comparable to the size of Naiad, the smallest moon that they did find. This object is quite a bit smaller than Naiad.

By the way, the Uranian moon Cupid, discovered in Hubble images in 2003, was also too small for Voyager to detect.

[Ian R]

Is my memory deceiving me, or has Naiad eluded all attempts at its recovery since the Voyager encounter?

[Hungry4info]

AFAIK, that's correct.

[Hungry4info]

And on that topic, Naiad has now been recovered.
http://www.seti.org/seti-institute/press-r...lost-inner-moon

http://www.universetoday.com/105361/a-tale...-and-its-rings/

Attached thumbnail(s)

 

[Bjorn Jonsson]

A few hours from now, on August 25, 2014 at 03:56 UTC, there are exactly 25 years from Voyager 2's closest approach to Neptune.

I have noticed that mosaics of Neptune are rare, the only mosaics I remember seeing are two global cylindrical maps that first appeared in Science back in 1989 and also the mosaics posted by machi earlier in this thread. So I decided to do some anniversary mosaics. The goal was a global (or near-global) color mosaic and the higher the resolution the better. This resulted in the highest resolution global mosaics of Neptune I have seen (but see the processing description below - maybe it can be argued that these images are in the gray area between mosaics and computer generated images/simulations):





There are two versions of each mosaic, an approximately true color/contrast version and a version where contrast has been greatly exaggerated and the effects of global illumintaion removed.

Some notes on the image processing: Voyager 2 usually had to transmit everything to Earth in real time. At the low bit rates possible from Neptune's distance from Earth this meant a long time between successive images. This makes assembling mosaics of Neptune difficult since the images that must be used are obtained over a period of many hours (or even a few tens of hours for big mosaics) and Neptune rotates fast. The best way for assembling big Neptune mosaics is to reproject the images to simple cylindrical projection as I typically do when doing mosaics of Jupiter or Saturn. But in addition I had to remove the effects of global illumination using an inverse photometric function when reprojecting the images, otherwise seams in the map can't be removed with acceptable result. In contrast, this is not the case when dealing with Jupiter or Saturn. I then assembled a mosaic in simple cylindrical projection and then rendered images of Neptune using the appropriate photometric function. This results in some photometric innaccuracies (the photometric function isn't 100% accurate) but despite this the resulting global images are much better than what one gets by using the source images directly since the illumination conditions change fast due to Neptune's fast rotation. All of this was done in grayscale as only green and clear filter images were available. I used mainly green images since they had better contrast than the clear filter images.

In addition to the complications mentioned above, some of Neptune's atmospheric features change very fast (especially the bright clouds) and also the rotation period (or zonal winds) varies a lot with latitude. Major features can drift over 60° in longitude during one rotation of the planet. Because of this the relative longitudinal positions of the cloud features are only approximate in the mosaics above.

The final step was to colorize the grayscale renders. For that I used an earlier global true color image I assembled back in 2009 - it can be seen here.

With all of the caveats above, the result is the highest resolution global mosaics of Neptune that I have seen.

Most of the source images I used were obtained about 2 to 3 days before closest approach when Voyager 2 was 3 to 4 million km from Neptune. I used the calibrated and geometrically rectified images available at the PDS Planetary Rings Node. I used about 20 images.

[Ian R]

Bjorn, I am in awe of what you've achieved here. Simply magnificent: a real masterclass in working with old yet valuable data.

[machi]

Excellent as always Björn!
I think that those images are the best global mosaics of Neptune ever made.

[tedstryk]

Amazing. Just amazing.

[jccwrt]

The other day I found an image of Despina's shadow transiting across Neptune in Voyager 2 images taken on August 17. I've seen the wonderful pictures that Ted Stryk and Daniel Macháček have made with moon shadows transiting, but I wasn't sure how much searching they had done for those. So I decided to do a thorough, systematic search through Voyager 2's approach images to see what turned up.

My first step was to download all of the c112xx images taken through Voyager's narrow-angle camera, and search visually through the images for potential moon shadows. Despina's shadows were easy to find, but I also came across some smaller spots that were only about 1 px across, but appeared to be features I could follow from image to image. I kept a spreadsheet of all potential shadows and the images they were found in, then cross-checked them with the PDS Neptune Viewer to see if any of the moons were in positions where they could cast shadows on the planet. Sure enough, a few of those iffy identifications coincided with Naiad and Thalassa approaching the limb of the planet.

Once I had identified a few shadow transits of Despina, Thalassa, and Naiad, I generated a table to predict the times that their shadows might fall on the planet. To do this I simply found an image where the moon's shadow was close to 2nd or 3rd contact, then multiplied by the moon's orbital period. Table in hand, I went through and checked those times against what Voyager was taking pictures of to see if the camera was pointed at the planet during a transit period, and if so, if it got a picture of the moons' shadows tracking across Neptune. I expanded this second pass through the data to include wide-angle camera images starting on the 16th. During this second pass I turned up a few more transits.

Here's a sampling of what I turned up:

Despina's shadow, followed about 10 minutes later by Thalassa's shadow. The gif is enlarged by 2x for better visibility. Here I've applied a 3px unsharp mask to increase contrast and bring out some subtle detail in the clouds:



Thalassa and its shadow on the planet at the same time. The inset is 2x the original resolution. I just stretched the histogram here, unsharp masking didn't really bring out any additional detail:



Naiad's shadow on August 24 through the wide-angle camera. The inset is also at 2x, and has had a 3px unsharp mask applied to increase contrast between the shadow and the clouds.



In addition I was able to identify the spots on Daniel Macháček's photo in the OP as the shadows of Despina and Thalassa, with a guest appearance by Thalassa itself.

My final tally:

18 transits of Despina, with the first observable on August 8. There were 6 more transit events between August 7 and August 24 where Voyager was observing Neptune when Despina's shadow was crossing the disk, but the images were either blurry or the shadow wasn't detectable. I may have seen a shadow in two of these events, but it was only present in a couple of images and may just be noise. The image sequence that Ted Stryk discovered, c1138023-56, appears to be the only set that captured Despina or its shadow through the narrow-angle camera within a day before Voyager 2's closest approach.

9 transits of Thalassa, with the first observable on August 16. There were 4 additional events between August 15 and August 24 where Voyager was looking at the right time, but 3 of these were taken through the wide-field camera on August 22-23 and I wasn't able to see Thalassa's shadow in any of the images taken during this time. No Thalassa transits are visible through the narrow-angle imager within a day before Voyager 2's closest approach, but frustratingly a narrow-angle image, c1136125, would have captured a high resolution image of a Thalassa shadow transit had it been taken about 10 minutes later.

9 transits of Naiad, with the first observable on August 17. There were 4 additional events between August 15 and August 24 with Voyager looking at the right place at the right time. It appears that Naiad's shadow was just below the detection limit in three of these, and the fourth was only visible when Voyager was taking UV images, which have a really low S/N ratio. No Naiad transits are visible through the narrow-angle imager within a day before Voyager 2's closest approach, although it does appear twice in wide-angle images taken on the 24th. The highest resolution views may be the last narrow-angle images to see Naiad's shadow, c1124332-58, back on August 20.

Finally, I was unable to find any shadow transits of Galatea visually, and without that I was unable to generate table where there were windows of opportunity for Voyager to see its shadow. I did search around in Neptune Viewer time periods between August 15 and 18 when Galatea was approaching the limb of the planet and was in position to cast its shadow, but didn't turn up anything. It seems that the shadow either grazed the northern limb of the planet and lasted less time than the gap between images (usually 9 minutes) or missed the planet entirely. No ring shadows were seen, and as Ted Stryk suggested in his conference paper, they are likely well below Voyager's resolution limits.

Not sure where to take this from here. The shadows are much too small and fuzzy to really do much to improve the shape model of these moons, although I suppose they might be usable in refining the moons' orbits if they had some precise astrometry done. Mostly just enjoyed the challenge of finding these things as far back in Voyager's encounter as possible.

[Ian R]

Fantastic work!

[tedstryk]

I worked through these images with Mark Showalter after finding the intitial set. The images are certainly interesting, although given the long baseline with Hubble, they unfortunately didn't prove very useful.

Nice work with the images.

[jccwrt]

It's a shame to hear they're not too useful, but I'm not surprised given the somewhat spotty quality of the images.

[DrShank]

this was my attempt 20 years ago to cobble together a complete mosaic of the Neptune ring system. by coincidence, none of the arcs was in view in any of the shots taken during this long sequence. reminds me i should redo this and try to get rid of some of the artifacts . . .

Attached thumbnail(s)

 

[vikingmars]

this was my attempt 20 years ago to cobble together a complete mosaic of the Neptune ring system. by coincidence, none of the arcs was in view in any of the shots taken during this long sequence. reminds me i should redo this and try to get rid of some of the artifacts . . .

Wow ! What a nice image ! Thanks a lot

[MarcF]

Nice new pictures of Neptune by Hubble, confirming a new Dark Spot with its bright companion in the southern hemisphere !
Reminds me the great time of Voyager 2 flyby. Even if these Hubble images do not have the Voyager 2 resolution, they are quite good and confirm that great science could be made from Earth orbit !
Can't wait the first planetary views from JWST... and from a Neptune-dedicated mission (?)
http://www.nasa.gov/feature/goddard/2016/h...spot-on-neptune
Regards,
Marc.

[jccwrt]

A few recent Neptune projects:

Here's a narrow angle frame from August 20, I think there's a JPL version floating around. However, it still has the scanline artifacts, and is so deeply saturated that it looks like a monochrome image that's been painted a single tone of blue.


Narrow angle frame of the Great Dark Spot rotating into view on late on August 23. I did some blending of narrow angle clear and green filter images to get more of the limb in view while retaining some of the sharpness of the cirrus clouds. Color is taken from wide-angle images taken simultaneously. Some of the color noise has been suppressed using the Deep Sky Colors HLVG plug-in. Not super happy with the results but I think it's the best I'm going to get considering the available data.



Finally a departing shot of Neptune and Triton on August 31. Dark Spot Jr. is near the cusp on the left, as well as a cluster of cirrus clouds that often popped up over the spot. Dark cloud bands around the south pole are also unusually clear in this image. Not sure why.

[Floyd]

Very nice. The geometry of the Neptune and Triton image is stunning.

[Ian R]

The Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), is a new instrument designed by Princeton to observe exoplanets, and works in conjunction with the Subaru Telescope in Hawaii. It has also returned a quite astonishing image of Neptune:

http://www.universetoday.com/131903/prince...d-nearby-stars/

[JRehling]

That's a great image; I've seen an even sharper image of Ganymede, which I won't link because it's off topic. And the instrument isn't designed for Neptune but, in a nutshell, instruments with resolutions better than 0.01 arc seconds /pixel are now becoming available, which means that we can track features hundreds of km in size, maybe even under 100 km. That means that Neptune could be tracked almost continuously for the ~3/4 of the year when it's not lost in daylight. And echo that for Uranus, with 50% better detail. Indeed, with a lowly 6-inch telescope, I've imaged clouds in visible light on Uranus, which, owing to the seasons, Voyager 2 didn't even accomplish! It's a new era for the outer planets.

[algorimancer]

...I've seen an even sharper image of Ganymede, which I won't link because it's off topic...

I'd love to see that Ganymede image. Any chance you could post the link, perhaps in the appropriate category?

[JRehling]

I'd love to see that Ganymede image. Any chance you could post the link, perhaps in the appropriate category?

I posted it here:

http://www.unmannedspaceflight.com/index.php?showtopic=8253

[Astroboy]

1989-08-27T20:48:45-21:06:21, stabilized and interpolated to 1 frame per 96 seconds (I wanted to match the maximum frame rate the Voyagers were capable of). Some tiny bits of it don't interpolate well, but the compression of the gif hides those errors.

[TheAnt]

1989-08-27T20:48:45-21:06:21, stabilized and interpolated to 1 frame per 96 seconds.

Fantastic glimpse you provided us with there. =)

[Astroboy]

I decided to do a rotation movie of an iconic view from Voyager 2 of Neptune on August 17, 1989. It is in Voyager OGB-o-rama, interpolated to 10 minutes per second from three or four frames of each record. I copied Ian Regan's brilliant idea of injecting the spacecraft movement back into the video, and took it one step further by putting the reseaus back in. I geometrically corrected a raw dark current calibration image using the GEOMA program in VICAR but didn't erase the reseaus or clean or calibrate it in any way, keyed out the dark current, and laid the reseau image over my video. There is very little subjectivity here - you see more or less exactly what the narrow angle camera saw during this sequence, with only geometric and radiometric calibration and removal of digital artifacts. Personally, I love the reseaus - you know you're looking at images taken with an old, analog spacecraft camera when you see them.

https://vimeo.com/235197221

[Hungry4info]

Supersharp Images from New VLT Adaptive Optics
https://www.eso.org/public/news/eso1824/?lang

Rather impressive Neptune image.

Attached thumbnail(s)

 

[Explorer1]

Amazing! Triton's disc could also be resolved, I believe? The Hubble-VLT comparison in the link would point to that being a possibility.
Just wetting our appetites for a when a spacecraft finally returns to the ice giants (decades from now...)

[antipode]

Amazing image, although I hope the EELTs will do better (and faster than the next ice giant mission).

Although orbiters are badly needed to both, I wonder if cheaper New Horizons-like flybys might not be more likely
as long as there is suitable geometry for a subsequent large (spherical) TNO flyby after? So many are binaries you'd
get quite a lot of bang for the buck.

p

[JRehling]

Here's a state of the art image of Ganymede using the 5m Hale Telescope.

http://www.unmannedspaceflight.com/index.p...st&p=233427

The ELT (named changed from the previous E-ELT) will have 8 times the aperture, and Neptune is roughly 8 times more distant than Jupiter, so that indicates the resolution that will be possible for the Neptunian system and similarly distant objects such as Pluto. Of course, the ELT will not be dedicated to Neptune observations. I think we can safely say, however, that global Neptunian weather patterns can be tracked by other multi-meter telescopes from the ground and so the return-on-investment of Neptune missions decreases accordingly.

For fine detail of the planet and satellites, of course, there's no substitute for being there.

I think one of the best value propositions for Uranus/Neptune missions would be a flyby that targeted one of the larger TNOs and used the ice giants for a gravity assist on the way there. Four such missions could capture >75% coverage of selected satellites (obviously, Triton being one) and then provide an encounter of, potentially, New Horizons type value at Makemake, Haumea, etc. with great synergy in designing and manufacturing four identical craft with New Horizons legacy tech.

I don't see how a Uranus or Neptune orbiter could possibly jump the queue over many potential ambitions to closer targets of very high interest, Enceladus and Titan to name just two.

[jccwrt]

A recreated view of the Neptune system as seen by Voyager 2 at approximately 1615 UT. I picked this time because Voyager made back-to-back observations of Neptune and Triton, so the appearance of these bodies closely approximates what a simultaneous view would have looked like.


Neptune and Triton - Voyager 2

I used a wide-angle OGV shot of Neptune and a narrow-angle GV observation of Triton. I recreated the view using a Neptune Viewer plot taken at the center of the Neptune observation, and then placed the reduced-size image of Triton in the appropriate positions. The slight difference in the direction that the crescent horns point is real - their position relative to the Sun was close enough that the phase angle was different from Voyager's point of view.

There is one improvement that I can think of. Neptune's remaining "major" moons should have been present in this scene as well, but I am not sure about their visibility to an observer at Voyager 2's location. Their small size and the position of the spacecraft suggest that they would only be a pixel or two across in the wide-angle camera and most of that surface would be in darkness. I am planning to look through some Neptune images taken a couple hours later where Galatea and Thalassa are present in the frame, which should help me determine if including them in this image would be appropriate.

[jccwrt]

Working with some of my eclipse calculations from a few years back - I wanted to see if there were any interesting color sets of shadow transits at moderate resolution. I did find a decent set involving Despina's shadow early on August 24 through the WAC. Neptune itself is an OGV natural color image, but I have composited in the moons from several separate images. All three moons visible within this image are brightened by about 10x. (Naiad and Thalassa should both be theoretically visible but were below the detection limits with this exposure setting.)

[MarcF]

Nice new article in Nature about the inner moons of Neptune
The latest discovered inner moon of Neptune has now a name : Hippocamp
https://www.skyandtelescope.com/astronomy-n...campaign=buffer

From the paper:
"Hippocamp orbits close to Proteus, the outermost and
largest of these moons, and the orbital semimajor axes of the two
moons differ by only ten per cent. Proteus has migrated outwards
because of tidal interactions with Neptune. Our results suggest that
Hippocamp is probably an ancient fragment of Proteus, providing
further support for the hypothesis that the inner Neptune system
has been shaped by numerous impacts."

Also, Naiad hadn't been seen since Voyager 2's flyby. Showlater's team did spot it — but in a spot diametrically opposite where it should have been, based on the presumed orbit. Thalassa (92 km) proved less challenging but was still displaced 19° from its predicted orbital longitude. The team also reports that no other moons larger than 24 km likely lie within 200,000 km of Neptune or larger than 20 km farther out.

The ring/inner moons system of Uranus was known to be a very dynamic system. The same seems to be true with Neptune ring/inner moons system.
Regards,
Marc.

[TrappistPlanets]

Was any parts of Neptuneshine on triton visible during the closest approach?

[JRehling]

The timing of the Voyager 2 encounter at Neptune was almost perfectly wrong for such opportunities. Triton's Neptune-facing hemisphere was in sunlight at the time of the encounter.

[TrappistPlanets]

The timing of the Voyager 2 encounter at Neptune was almost perfectly wrong for such opportunities. Triton's Neptune-facing hemisphere was in sunlight at the time of the encounter.

so at what point in the encounter gives us the higher quality neptuneshine sense closes point it was in sunlight

[Phil Stooke]

If I am remembering this correctly, when Voyager 2 flew past Triton, Triton was the most distant known object in the solar system. Pluto was near perihelion and closer to the Sun, and the KBOs we know today had not been discovered yet. Triton was beyond Neptune and Nereid was closer to the Sun.

Phil

[john_s]

Actually there would have been some Neptune-lit terrain visible to Voyager during the close Triton flyby- the sunlit terminator extended to about 40 degrees north, but the Neptune-light terminator would have reached ~90 degrees north, and the intervening parts of the northern hemisphere were in direct view from Voyager 2 on approach (as Voyager was coming almost directly from the direction of Neptune). Lighting was poor, though- Neptune was a crescent as seen from Triton at the time, and of course even sunlight illumination was challenging for imaging with Voyager's vidicon at Neptune. I don't recall seeing any successful detection of Neptune shine on Triton in the Voyager data.

John

[TrappistPlanets]

Actually there would have been some Neptune-lit terrain visible to Voyager during the close Triton flyby- the sunlit terminator extended to about 40 degrees north, but the Neptune-light terminator would have reached ~90 degrees north, and the intervening parts of the northern hemisphere were in direct view from Voyager 2 on approach (as Voyager was coming almost directly from the direction of Neptune). Lighting was poor, though- Neptune was a crescent as seen from Triton at the time, and of course even sunlight illumination was challenging for imaging with Voyager's vidicon at Neptune. I don't recall seeing any successful detection of Neptune shine on Triton in the Voyager data.

John

Ted Stryk did got a huge amount of neptuneshine on Triton but it was on a low res departer image, and i like some higher quality neptuneshine even if its just a part of it and not all of it

https://cdn.discordapp.com/attachments/7275...t_of_triton.png

where is the pole, i tried reprojecting this (above (link) before but i think my attempt was wrong so where is the pole?

[TrappistPlanets]

Ted Stryk did got a huge amount of neptuneshine on Triton but it was on a low res departer image, and i like some higher quality neptuneshine even if its just a part of it and not all of it

https://cdn.discordapp.com/attachments/7275...t_of_triton.png

where is the pole, i tried reprojecting this (above (link) before but i think my attempt was wrong so where is the pole?

here is my newest attempt (from today (credits to sckenk and ted)

[JRehling]

so at what point in the encounter gives us the higher quality neptuneshine sense closes point it was in sunlight

In principle, there would have been some time after the encounter when Triton was in a "new" phase as seen from Neptune, but Voyager 2 would have been very far away at that time. Voyager 2 was moving very fast when it passed Neptune, entering and then leaving proximity in well under a day. Triton would have taken about three days to get back around to a "new" phase.

[TrappistPlanets]

In principle, there would have been some time after the encounter when Triton was in a "new" phase as seen from Neptune, but Voyager 2 would have been very far away at that time. Voyager 2 was moving very fast when it passed Neptune, entering and then leaving proximity in well under a day. Triton would have taken about three days to get back around to a "new" phase.

did i reproject the neptuneshine correctly in the map above your post?


okay so what image of triton would give us the highest quality chunk of neptunshine of ted were to pull it out?

[ZLD]

New Hubble data products on the 2018-2020 Neptune spot evolution were just released.

https://archive.stsci.edu/hlsp/nds-2018

Looks like the current paper isn't open access (yet). Previous paper from the same group (open access): https://agupubs.onlinelibrary.wiley.com/doi...29/2019GL081961

[StargazeInWonder]

The Neptune imagery at the first link is really fantastic. It seems easy to see how the major patterns are evolving over a few years.

[titanicrivers]

Nice JWST image of Neptune's rings on today's NASA Webb page here: https://www.nasa.gov/feature/goddard/2022/n...ings-in-decades

[Phil Stooke]

Great image of the rings.

If you take a radial sample of the rings you can map the brightness variation. Take lots and you can average them. Here I have averaged many radial samples to create a synthetic view of just the rings in a polar view. I don't see any sign of the clumps in the rings in the original image, but even if present they would be erased by the averaging process here.

Phil

[titanicrivers]

Hey Phil, can you explain a bit how to 'take a radial sample' as you did in your post above. Thanks

[Phil Stooke]

Simplest approach:

The oblique view makes the rings look like an ellipse. draw a line through the long axis of the ellipse and measure the brightness along it. Add the left and right sides together to reduce noise, and rotate that in a circle.

More sophisticated: stretch the image perpendicular to the long axis so the rings look circular. Take multiple radii out through the rings in the sectors which are less obstructed by the planet itself. Add together to get an average and rotate that in a circle.

My version was more like the second.

Phil

[Ian R]

86 wide-angle Voyager 2 frames were merged to create this view of Neptune, two of its brightest rings, and many background stars. The clear filter images were obtained on August 26th, 1989, over a period of 19 hours as the spacecraft departed the ice giant.

[Ian R]

Over 24 hours, on August 31st, 1989, Voyager 2 collected 182 narrow-angle clear-filtered frames. Together they create this view of Neptune, the Adams and Le Verrier rings, and some background stars. The planet's shadow cuts across the Le Verrier ring at top center.



Edit: replaced with superior version.