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Cassini "Kodak Moments"
John Flushing
post Mar 1 2007, 03:27 AM
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Cassini took a picture when it was travelling fairly close to Saturn. To me, it looked similar to some pictures of Earth taken by people on space shuttles in orbit. For that reason, I decided to put Bruce McCandless into the photograph of Saturn.



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JRehling
post Mar 1 2007, 05:43 PM
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Tons of new Saturn-and-rings pictures today. Check JPL Photojournal.

Check out

http://photojournal.jpl.nasa.gov/catalog/PIA08361

but don't panic... Saturn is still there.
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Guest_AlexBlackwell_*
post Mar 1 2007, 05:56 PM
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There's a brief image advisory on the Cassini website.
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ugordan
post Mar 1 2007, 07:11 PM
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Note a peculiar thing in this image. Bjorn noticed it back in Ian Regan's mosaic that the rings were too bright around the planet's shadow. The feature is obviously real, the question is: how come? Phase angle effects, similar to opposition effect but on the unlit side? Weird...


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JTN
post Mar 4 2007, 03:32 AM
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(Only tenuously thread-related, sorry...)
Just noticed a satellite shadow on Saturn in the raws (1, 2, 3, 4). We don't see that very often, although I guess it'll become more and more common as we approach the solar ring plane crossing in 2009.
(Note: some frames were reduced in size in the animation.)
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ugordan
post Mar 4 2007, 12:31 PM
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Nice catch there, JTN! Any idea which moon that might be? Mimas? Celestia seems to suggest so.
The raws are all a clear filter so the sequence probably targeted this shadow specifically.


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JTN
post Mar 4 2007, 02:35 PM
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QUOTE (ugordan @ Mar 4 2007, 12:31 PM) *
Any idea which moon that might be? Mimas?

After some noodling about with Mark Showalter's tools, I think that it might be Mimas or perhaps Enceladus, with the images taken over the space of an hour or so around 2007-03-02 17:00-18:00 (Saturn Viewer time, whatever that is).
Unfortunately I don't think Saturn Viewer plots satellite-on-primary shadows (or at least I couldn't get the Jupiter viewer to show any of the shadow transits from NH, where we know the times -- see also this topic), and doesn't have a "view-from-Sun" option (just "view-from-Earth").
(This is much harder with jmknapp's raw image analysis out of action. What happened to Joe, anyway? He hasn't posted in nearly a year.)
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scalbers
post Mar 4 2007, 02:55 PM
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I'm trying to remember whether Celestia can render shadow transits? It would be able to show the "from Sun" view at least (in addition to from Cassini).


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Rob Pinnegar
post Mar 4 2007, 03:28 PM
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We'd expect the first satellite shadows to be Mimas and Enceladus, then the other moons from the "inside out".

Hey, speaking of which: Saturn eclipsed Iapetus a week or two ago. I wonder if that means Iapetus' shadow will pass over Saturn (or, almost as interesting, over the rings) in a couple weeks' time?

It'd be a transit rather than an eclipse, and Iapetus will only block maybe a quarter of the Sun's light, but it might be perceptible. Time to get out the Solar System Simulator.
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nprev
post Mar 4 2007, 03:46 PM
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Hmm...how big would Titan's shadow appear on Saturn? I don't recall offhand ever seeing reports of any surface-based visual obervations of this during equinox, which is kind of odd.


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JTN
post Mar 4 2007, 04:13 PM
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QUOTE (nprev @ Mar 4 2007, 03:46 PM) *
Hmm...how big would Titan's shadow appear on Saturn?

About this big wink.gif Note also the satellite shadow across the rings in the lower image. I'm hoping for similar views from Cassini in 2009.
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nprev
post Mar 4 2007, 05:17 PM
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OH yeah! smile.gif Thanks, JTN; 2009 should indeed be an interesting year!


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helvick
post Mar 4 2007, 07:14 PM
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QUOTE (scalbers @ Mar 4 2007, 02:55 PM) *
I'm trying to remember whether Celestia can render shadow transits? It would be able to show the "from Sun" view at least (in addition to from Cassini).

Yes it can - this was the first definite Titan transit of Saturn date I could find online - from Dec 25 1877 @ ~5:46.

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JTN
post Mar 4 2007, 07:30 PM
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QUOTE (helvick @ Mar 4 2007, 07:14 PM) *
Yes it can - this was the first definite Titan transit of Saturn date I could find online - from Dec 25 1877 @ ~5:46.

That shadow seems rather small for Titan. Titan's radius is about 1/23 Saturn's (excluding atmosphere). I realise there are penumbral effects to worry about, but the Hubble pic above matches that ratio reasonably well.
(Celestia's great and all, but I stopped trusting it for this sort of thing when I saw what a cop-out Epimetheus/Janus were wink.gif )
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Stu
post Mar 4 2007, 07:42 PM
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this was the first definite Titan transit of Saturn date I could find online - from Dec 25 1877 @ ~5:46.

I believe an ESA probe took some pics at the time, and they're due for release "soon"... wink.gif


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