Juno at Jupiter, mission events as they unfold |
Juno at Jupiter, mission events as they unfold |
Jul 5 2016, 07:53 PM
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
This topic will consist of discussion of Juno operations post-JOI until end of mission, currently anticipated in Feb 2018.
-------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Jul 27 2016, 11:09 AM
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
To find out the limiting magnitude for stars and possibly moons for JunoCam's TDI 4 images, I've stacked (summed two averages of 16 images in this case) 32 log-stretched processed Jupiter Approach images, and stretched the result roughly with a square root function after subtracting some constant bias. The limiting magnitude seems to be near vmag 1.0. Rigel, Betelgeuse, and Aldebaran can reproducibly be processed out. Other stars of Orion or Taurus seem to be invisible or ambiguous at least.
But I hesitated to post the image yesterday as it has been, since there are several properties and features to be explained: - The image is heavily stretched, and therefore shows much image noise. - The stars look almost white. In smaller stacks, Betelgeuse and Aldebaran look reddish, as to be expected. - The vertical stripes are processed compression artifacts. - Narrow vertical lines, interrupted or not, are mostly summed hot pixels. - Faint objects appear to induce a darker environment in lossy DCT (compression) blocks. - Jupiter's Galilean moons average almost away due to their motion. Only their dark compression artifacts remain well-visible in the stacked image. - There is a horizontal brightish stripe through Jupiter, and extending horizontally across the image. This is likely explainable as subtle lense flare, although I didn't find a documentation about the appearance of JunoCam's lense flare. Near Jupiter, the averaged moons might add some brightness. I cannot disambiguate, whether a ring adds visible brightness. - There is a vertical brightish feature north and south of Jupiter (south is up). This seems to be independent of the position of the moons, hence cannot be explained away by a lack of dark compression blocks. Thus far, I can't rule out a lossy image compession side effect of Jupiter, lense flare, and some real feature like hot hydrogen. But the latter is no way evident from the image. |
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