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Unmanned > Outer Solar System > Uranus and Neptune
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.
Yes!!! smile.gif I was hoping you'd focus your imaging magic towards Neptune!
It was only matter of time. smile.gif
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.
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.
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.
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!) smile.gif
Ian R
Are these the famous shadow-casting cirrus clouds, I wonder?

Click to view attachment
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.

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.
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).
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'?


"Really enjoying this thread"

I am glad to hear that. tongue.gif

"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:
Wow, that animation's smooth; had to look hard twice to see that the white clouds were really moving. Nice!!!
Stop that Machi. You're making my eyes hurt blink.gif
Wow! That was neat! It gave the impression of just sitting there watching Neptune silently rotate underneath.
That is so relaxing to watch! Amazing work machi smile.gif
Holy smokes, machi -- that's gorgeous.
That slow motion beauty could make it the opening scene for Stanley Kubrick's grandson's film 2041 A Space Iliad.
Yeah, there's definitely something @ the South Pole...can't tell if it's an innie or an outie, though.

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.
Partial mosaic of Neptune. Four NAC images over WAC image.
Color from CH4JS, CH4U and violet WAC images.
Another partial mosaic of Neptune. Now at resolution 10.5 km/pix.
Color is added from global images (as uniform color).
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.

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

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?

Some more informations can be found here:

"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."
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.)
I found even a nicer movie:
Best regards,
New Neptunian moon discovered
I was wondering: being so close to the planet, any chances that it was already present in Voyager imagery?
The article says the discoverer couldn't find it in them.
QUOTE (Explorer1 @ Jul 15 2013, 08:56 PM) *
The article says the discoverer couldn't find it in them.

they seem to have updated it since I posted my comment...
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?
AFAIK, that's correct.
And on that topic, Naiad has now been recovered.
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):

Click to view attachmentClick to view attachment

Click to view attachmentClick to view attachment

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