Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread |
Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread |
May 18 2007, 09:43 PM
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#31
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
I've been processing some of the high resolution Galileo Ganymede images recently. As far as I know the two mosaics below have not appeared at the official websites (at least not in this form) so in a sense they are 'new'.
The first one was obtained during the G1 flyby in 1996. It covers a part of Memphis Facula which is centered at roughly 15°N, 132°W. The images were obtained at a distance of approximately 5000 km from Ganymede's center. The second one was obtained during the G28 flyby in May 2000. It is centered near 14.5°S, 319.7°W. The images making up the mosaic were obtained at a distance of roughly 4500 km from Ganymede's center. I will probably post more Ganymede mosaics later this month or next month. |
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May 26 2016, 02:37 AM
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#32
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Member Group: Members Posts: 306 Joined: 4-October 14 Member No.: 7273 |
Voyager 2 got a great mosaic of the ~600 km wide Gilgamesh Crater, which was sitting near the sunset terminator around the time of the flyby. With normal image processing it's pretty easy to see the ~300 km inner basin, as well as the scarp surrounding hummocky terrain that marks the edge of the main crater at a diameter of 590 km. To the south of the crater, there is a hint of some smoother terrain, but it's hard to interpret.
Full-size here When I was processing this, I accidentally pasted in another copy of this photo in a difference blending mode. As it turns out, a slight offset highlights the surface roughness pretty well, and the smoother terrain really pops out: Full-size here Reading Paul Schenk's paper on Gilgamesh, this zone is interpreted as a continuous ejecta sheet, which extends out about 1,100 km from the crater's center. |
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May 26 2016, 06:50 PM
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#33
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
This is all fantastic. Ganymede is truly one of the more beautiful worlds. As I've gotten into astrophotography over the last year, I've learned quite a bit about deconvolution; it may be more accurate to say that I've used deconvolution. I have found myself saying, "This is where the magic happens" as I watch blurry images suddenly become wonderful through processes I can only partially explain.
This goes a bit off the title subject, but I obtained the following image of Ganymede using a NexStar 6se and deconvolution, with the single aim of seeing if I could resolve surface features, and it worked better than I expected. I imaged Ganymede when Galileo Regio was centrally aligned, and I certainly succeeded in resolving it. This image is with a green filter: The color image I got from RGB was not so good, so I'll just offer the green version alone. I'm not sure I know of anyone else getting surface details with a telescope of this size. |
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May 27 2016, 01:43 PM
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#34
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Junior Member Group: Members Posts: 64 Joined: 17-December 12 From: Portugal Member No.: 6792 |
... I'm not sure I know of anyone else getting surface details with a telescope of this size. That darker detail, so well centered on the disk, seems a bit like a processing artifact. Or your secondary mirror ;-) Extreme processing on images so small (compared to the theoretical resolution) can be tricky. The limb's contrast with the dark background can be enough to create a "doughnut" or ring effect. But if you can get more images and do a rotation movie, I'd be convinced ;-) -------------------- www.astrosurf.com/nunes
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Mar 6 2017, 03:42 AM
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#35
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
That darker detail, so well centered on the disk, seems a bit like a processing artifact. Or your secondary mirror ;-) Extreme processing on images so small (compared to the theoretical resolution) can be tricky. The limb's contrast with the dark background can be enough to create a "doughnut" or ring effect. But if you can get more images and do a rotation movie, I'd be convinced ;-) This challenge sat in the back of my mind for 9 months, until Jupiter opposition came back around. I had good seeing three nights in a row last week, when Galileo Regio happened to rotate into and out of view My animation, paired with Solar System Simulator plots, is attached. These are images taken with my 150mm NexStar 6se and a broad blue filter, stacking 1500 frames. Images taken with a green filter look quite similar. Images taken with a red filter, however, do not show Galileo Regio. I've now noticed this on four different dates – one last year and three this year. After examining Cassini images of Ganymede, I find no reason for that in terms of Ganymede's actual color/terrain. Here's my conclusion: I have just enough resolution to capture Galileo Regio in shorter wavelengths. In red wavelengths (~40% worse diffraction-limited resolution), I can't capture it, so my color image shows Galileo Regio as red, which is a total artifact. Nevertheless, I feel assured now that I have imaged Galileo Regio, which pretty much maxes out the resolution I can hope for with my gear. |
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