Problem with Saturn's moon Pan and the Encke Division

[David Knisely]

Celestia shows Saturn's moon Pan orbiting correctly in the middle of the narrow Encke Division in Saturn's rings, but the rings show a "ringlet" right on Pan's orbital path. This needs to be removed, as there isn't much in that division that hasn't already been either swept up by Pan, or perturbed out of the division. It also makes it hard when "riding along" with Pan through the rings, as the ringlet keeps jumping around like one of the planetary orbits.

[selden]

I'm not the person who created the original ring image, but I thought I'd take some time today to look at Saturn's ring image file /textures/lores/saturn-ring.png

PNG files can contain an alpha (transparency) channel in addition to the main image. I used the netpbm utilities to split the file into separate alpha-channel and image files. As I suspected, the alpha channel in saturn-ring.png is misalighed with the main image. Its Enke's division is displaced radially inward from the Enke's division that's in the image. Other features seem to be similarly offset.

I've created a new png file with its alpha channel identical to the image itself. I'm not sure it's "right", but at least there's only one Enke's division, now

Oh, and before you complain about Pan not being centered in the gap, I checked around on the Web and found that its orbital parameters do indeed correspond to its being near the inner edge of the gap. It turns out that there also are more faint rings both inward and outward from the current ring image that Celestia's using. Creating an entirely new image is more than I'm prepared to do any time soon, though.

What I'd really like to see is a ring png file with an image that corresponds to the rings' measured brightness profile and an alpha channel that corresponds to their transparency. I'm rashly assuming there have been enough stellar occultations by the rings for that to be measured, of course.

Screenshots of Pan in Enke's division along with the revised png file are available on my Web site at http://www.lns.cornell.edu/~seb/celestia/gallery-001.html#7

[selden]

I spent some time Tuesday evening generating a proper ring texture file.
I fetched the reflection and transparency images from Bjorn Jonsson's site. I then scaled them and performed some minor surgery to align the major features. It's apparent that his images are not enitrely consistant. There seems to be different amounts of distortion in both.

Anyhow, here's a picture of it in use.

Pan can barely be seen in Enke's Division at the lower left.
Saturn's shadow on the rings is visible at the upper right.

The texture is available at http://www.lns.cornell.edu/~seb/celestia/saturn-rings-1024.png

Chris, please feel free to include the new ring texture in the next release of Celestia.

[David Knisely]

Thanks for making the change in the ring format image. I am demonstrating Celestial next week at our astronomy club meeting, and I knew that somebody would object to a "ringlet" in the middle of the Encke gap.

[selden]

sigh. I couldn't leave well enough alone...
You probably should download a new copy: Same name, same place, different file.

I was noticing that the rings seemed rather white. When I created the new ring png file I'd made a point of creating it as a grey-scale image. That may have been a mistake. The colors specified in solarsys.ssc didn't look like they were being applied.

I've updated the ring image to be "true color," although the colors themselves are still grey scale. Except for one pixel The ring colors now seem appropriately off-white.

But then I realized I'd had "ambient light" turned up to medium.
So now I dunno which actually fixed the colors: switching to a full-color ring image or turning off the ambient light. Oh, well.