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Neptune on August 25th---perhaps with white spot?

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#1 John Boudreau

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Posted 03 September 2013 - 07:59 AM

Here's a Neptune attempt from the early hours of August 25th. The image is from a stack of 5000 frames from a 6800 frame video, mid-point of which was at 0627UT.

I may have recorded the spot noted in recent captures by Pete Gorczynski on the lower right of the disk--- the longitude is similar to that of his result taken earlier that same morning. The camera was RA drift aligned so that celestial north is up--- which means that Neptune's N pole is pointed at about the 1:30 clock position. Although I didn't capture the pronounced brightening near the S polar region in results shown by others; the northern region has stronger limb darkening than the southern region.

The use of the ADC was due more to an experiment that night in using a W47 filter in my filter wheel to adjust the ADC while using the camera--- the deep red/near-IR leak of a W47 filter causes images of stars to be formed in both the deep blue/near UV and the deep red/near-IR. When adjusting the ADC one can see a star split into two components which can then be merged to indicate proper adjustment. In practice, imaging with a near-IR filter like the Baader 685 gains little benefit from an ADC --- it really only helps the shorter wavelengths noticeably when RGB imaging, so my next Neptune session probably won't include the ADC.

If I get another chance at Neptune soon I'll probably use my DMK21 with the more near-IR sensitive ICX618 CCD. Hopefully that will capture more of the deeper near-IR. And if all goes well in a couple of weeks I hope to be using my long-awaited 14.5" f18 Dall-Kirkham instead of the C11.

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#2 Sunspot

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Posted 03 September 2013 - 09:54 AM

Well, even if you didn't get the spot (I'm in no position to judge that...hehe) it's nice to get Neptune into the rotation.

When you get the 14.5" up and mounted, you need to post pictures. I think that scope and the ASI120 will be a great setup at prime focus.

Paul

#3 sfugardi

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Posted 03 September 2013 - 04:47 PM

John, excellent Neptune & Triton capture! I'm thinking of trying tonight with the Flea3 at prime or at f16 assuming the histogram is bright enough. Thanks for posting

Regards,
Steve

#4 John Boudreau

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Posted 04 September 2013 - 07:12 AM

Thanks guys!

Paul, I finally received the optics in late June after nearly a 2 year wait--- in part due to the original primary getting lost at the coater! However by that time I had a few other projects under way and haven't been able to commit the time to get the scope together quickly. But I'm sure it'll see light from Neptune and Uranus this month. It'll probably continue to be a WIP after first light as I figure out fan placement and other nuances.

Steve, I hope you had better skies last night than I had around here. At least up until 2AM here were still some thin clouds around that were thick enough to cause problems. I didn't bother to check later.

#5 Kecktastic

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Posted 04 September 2013 - 06:15 PM

Nice work John, great to see more people imaging Neptune & Uranus, so often they seem to get overlooked as legitimate amateur targets.

Cheers
Trevor

#6 Kokatha man

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Posted 04 September 2013 - 07:18 PM

.....like my recent comments about Paul's Uranus image I don't have the experience to interpret these images John, unless they were really flamin' obvious that is! :)

But a good effort nonetheless: one of the reasons I haven't actively tried to sell my Flea3 is because of the increased sensitivity in that part of the spectrum.....the ASI120MM got my "thumbs up" overall a long time ago (like, about a year now! :) ) but although I've managed quite a lot of good iR images of both Saturn & Jupiter with it, the response graphs clearly indicate the 618 sensors should be more effective...and with these more distant gas giants this superiority might still be quite tangible. :question:

At any rate from your's and others comments I'll have finally filled that 7th position in my EFW when the iR685nM filter arrives! :)

#7 stanislas-jean

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Posted 05 September 2013 - 03:55 AM

I tried yesterday evening to check the spot observed lastly around CM 20°. Nothing was seen during the period of observations. Sky was perfectly clear and transparent with stable images during 1-2 seconds time. Still the north hemisphere darker than the opposite one (may be with a lesser intensity). Nothing more except the vision of the planet satelite.
If the spot was present with the size given (1/4-1/5 planet diameter) and contrast revealed by ccd (more than the difference of the planet hemispheres), it would be visually accessible. Nothing was captured, if present the spot would be very low contrasted (less than the difference of the planet hemispheres).
Now the color channel of observations are not the same.
If this can be an help.
Stanislas-Jean

#8 John Boudreau

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Posted 05 September 2013 - 08:03 AM

Nice work John, great to see more people imaging Neptune & Uranus, so often they seem to get overlooked as legitimate amateur targets.


Thanks Trevor and Darryl!

Yes, I like to think we're entering a time when imaging planets that were largely previously neglected like Neptune, Uranus, and Mercury becomes more commonplace. The work that you guys have done with Saturn in following subtle atmospheric features is a superb example of stretching the boundaries of amateur imaging. Just imagine what our cameras will be like in 3 to 5 years! And stacking and processing software continues to improve too. As time goes on we'll be ever closer to our equipment's resolution limit for these more difficult targets as cameras become more sensitive. We're already there or at least in the ballpark for the brighter targets.

#9 John Boudreau

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Posted 05 September 2013 - 08:25 AM

Stan, if the spot (or perhaps series of spots) truly exists, it's may have a different size/shape than what appears in our images. In the PDM results this year it appears that a segment of a mid-latitude belt is noticeably brighter than the rest, and with our more typical smaller apertures and less sensitive cameras than used at PDM, we may be simply recording that as a bloated detection of an Airy disc --- for example, it's about the same apparent size as Triton is in our images (which is obviously not a resolved disc). Also, these results were taken with deep red or near-IR longpass filters so at least most of the light from the feature was probably recorded from the near-IR. Seeing and the longer exposure length required for such a faint target are certainly playing a role in limiting our resolution potential with these Neptune results. Hopefully the pros will get a look at it soon to determine what's really there.

Edit: I should have addressed your comment about image contrast. Any of the images you'll see from us showing features on Uranus or Neptune are very strongly contrast-enhanced. Much more so than anything you'll see in our visible light images of brighter planets. This even includes the work coming from PDM.

#10 stanislas-jean

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Posted 05 September 2013 - 12:09 PM

Thanks John for your comments.
Nevertheless what is disturbing this is the respective ratio of brightness of area on the disk, spot included which is significantly out of the difference between the hemispheres. This should be noticeable. I remember the Uranus case with the famous spot, faint and fuzzy, last opposition where when seen seemed to "float" above the planet structure. Nothing similar presently.
Now the image capture parameters as you said are amplifying so much the brigthness ratio so that we are involved to imagine effectively something not confidential. That is not.
For sure if the spot exists it is very faint in the yellow-red portion.
Bring data here about the issue of this spot event, that will help us about the perceptibility of such feature.
Thanks again.
Stanislas-Jean

#11 Pete Gorczynski

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Posted 05 September 2013 - 06:10 PM

Looks good, John. You certainly captured enough frames to get the job done. I'm wondering if you saw the brightening in just the raw stack before you applied any sharpening, just as I did.

Regards,

Pete G.

#12 John Boudreau

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Posted 05 September 2013 - 06:55 PM

Looks good, John. You certainly captured enough frames to get the job done. I'm wondering if you saw the brightening in just the raw stack before you applied any sharpening, just as I did.

Regards,

Pete G.


Thanks Pete. Yes, the bright zone can be seen in the raw stack, offset from the CM. I didn't push the sharpening beyond the first two wavelet sliders (Gaussian) because there would have been noticeable dark ringing around the spot. I had to use that many frames to control the noise though, as I was imaging at f18.8.

Seeing had been poor a couple of hours earlier--- the type of seeing where a star would only focus into a large fuzzy but steady blob despite the favorable seeing predictions. It eventually settled down to be pretty good seeing, but from that delay I didn't start recording until Neptune was well over an hour past the meridian.

#13 CPellier

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Posted 08 September 2013 - 12:56 PM

Very interesting John... to be repeated again :)

#14 Pete Gorczynski

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Posted 08 September 2013 - 01:07 PM

John,

I just realized that you captured this a few hours after I did. I analyzed you image and it appears to be the same white spot I got, except that Neptune rotated a bit.

Regards,

Pete G.

#15 Marc Delcroix

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Posted 10 September 2013 - 05:54 AM

Indeed, this is a nice confirmation of the true nature of the spot ...






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