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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May 27 2016, 05:42 PM
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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 ;-) Healthy skepticism, but I'm quite sure that it's real. I timed the image for when Galileo Regio was perfectly centered, so that is to be expected, and it was not centered in the vertical direction at all – very clearly in the north. This was also absent from previous efforts in imaging Ganymede with different central meridians. Here was an image of Ganymede taken about a day earlier, and a comparison image generated from maps. Galileo Regio is over where it should be – faint, but definitely not simply an artifact appearing dead center. I've tried and failed to get surface details on Io. I have probably gotten details on Mercury, but they're smudgy. Ganymede is an interesting challenge, but I don't think many astrophotographers even think of it. |
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