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Comparing Callisto's markings at varying distances

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#1 lcd1080

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Posted 26 October 2012 - 11:23 AM

The other day I posted a Callisto photo showing what may be albedo features rather than mere processing artifacts. One may note that the JPL Solar System Simulator depiction looks different from my photo however JPL's images are derived from close range spacecraft photos that show intricate surface patterns; these depictions differ in appearance from mine because an Earth based telescope captures only large scale albedo differences rather than intricate crater definition. For example in the images below note the photo of Callisto captured by the Voyager I spacecraft from a far away distance of 23 million miles; then look at the JPL Solar System Simulator image of Callisto from a nearby vantage point of only a few thousand miles. Note that Voyager's image shows only a few areas of light and dark rather than the intricate crater composition of the JPL simulator image. Similarly my Oct 17 2012 Callisto image shown below is similar to the Voyager I photo as it shows only a couple areas of light and dark on Callisto.

This was my first attempt to image detail on a Jovian moon so the pattern I captured may or may not be comprised of artifacts however based on the above analysis I believe that it may also reflect albedo features. When the weather finally clears I'd like to try again on Ganymede.

Pete

Posted Image

#2 DesertRat

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Posted 26 October 2012 - 12:24 PM

Interesting Pete. I've never seen detail myself when imaging Callisto. It always appeared as a dark nearly featureless object, sort of ghostly really. Now Ganymede is different, wish you luck there as it does have some nice features.

Glenn

#3 James W.

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Posted 26 October 2012 - 03:04 PM

Peter - Looks to me as if you have some noise in there or maybe it got there from the processing and that is what you are mistaking for surface details (blue and purple spots). IMHO!

#4 lcd1080

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Posted 26 October 2012 - 07:29 PM

Thanks Glenn, I'll give Ganymede a go when the weather improves. James I think that's a good idea you had about it looking as though I have some noise in my Callisto image that I'm mistaking for surface detail, particularly the blue/purple area; here's my red channel of the Callisto image which appears to have a better signal to noise ratio:

Posted Image

Now check out the following photo of Callisto that was an Amateur Astronomy Picture of the Day. It has a dark central area similar to my red channel; the detail is especially clear upon raising the gamma level to brighten the image:

http://aapod.astrono...d-Callisto.html

I'm not sure what if any conclusions can be drawn but I'm just trying to understand how much detail can be obtained from an amateur image of Callisto.

Pete

#5 James W.

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Posted 26 October 2012 - 09:31 PM

Here is my Callisto from the same night.

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