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Posted by: alan Jan 5 2006, 08:11 PM

Epimetheus, Titan and Dione?
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=59935

Posted by: ermar Jan 5 2006, 11:30 PM

Indeed it is! Playing around with the nifty http://pds-rings.seti.org/tools/viewer2_sat.html a bit, I get:



(or see the http://pds-rings.seti.org/work/viewer_sat_20902.jpg for more).

Posted by: JTN Jan 5 2006, 11:52 PM

Well spotted. http://www.cassinicam.com/sp/S17/req/ISS_019EP_MUTUALEVE008_PRIME.html appears to be the science plan entry.
Cheap'n'cheesy animated GIF http://www.chiark.greenend.org.uk/~jacobn/2006/01/cassini_20060105.gif (at 1.04MB, probably a little big to upload).
Towards the end you can also see a moon against the rings/disc which Saturn Viewer (indeed nifty; cheers, elakdawalla) http://pds-rings.seti.org/work/viewer_sat_20989.jpg as Pandora.
There also appears to be something tiny skirting along the bottom of the rings (the left in the original frames) which Saturn Viewer didn't identify, even with the maximum number of moons enabled[*]. It can be seen in many frames around the time Epimetheus transits Dione.

[*] These being: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus, Phoebe, Janus & Epimetheus, Helene, Telesto, Calypso, Prometheus, Pandora, Atlas, and Pan.

Posted by: alan Jan 6 2006, 04:08 AM

Whatever it is, it appears to pass behind Dione.

Posted by: ermar Jan 6 2006, 07:10 AM

Because it appears to pass behind Dione and because Dione was almost directly at its furthest from Cassini at the picture time, the target object (if a satellite of Saturn) must be in an orbit exterior to that of Dione. I tried matching the moon's ephemeris from Cassini's pictures with the named smaller moons (Kiviuq, Narvi, Ymir, etc) using JPL's http://ssd.jpl.nasa.gov/horizons.html, but couldn't find a match. I'd say it might be one of the as-yet-unnamed moons (the S/2004 bunch), except I doubt they'd be bright enough...

Posted by: Bob Shaw Jan 6 2006, 11:05 AM

That shape, it's somehow... ...familiar. Can't *quite* place it, though!
.
Burkhard Heim?

Bob Shaw

Posted by: Bob Shaw Jan 6 2006, 11:06 AM

That shape, it's somehow... ...familiar. Can't *quite* place it, though!
.
Burkhard Heim?

Bob Shaw

Posted by: pat Jan 6 2006, 12:18 PM

Its a star, TYCHO2-4696.09721, Mag 6.81 . Sorry.

Posted by: JTN Jan 6 2006, 12:46 PM

I thought that, but wasn't entirely sure; could the putative moon's brightness be such that it's not easily visible against the relevant part of Dione's disc?
The reason I ask is that Titan, Epimetheus, and Dione are all clearly behind the rings, and in the animation they are all moving left with respect to ring features. However, the mystery object appears to be moving right wrt ring/planet features, like Pandora, which, for a stationary observer wrt Saturn (such that only the moons' orbital motion affects this), would suggest that it's on the near side. (Which would be at odds with the fact that in the frame it appears closest to the far side of the rings, but that could be coincidence.)
However, on reflection, I believe Cassini's motion (although slow near apoapse) would cause a fixed background object such as a (bright?) star to behave this way too, and perhaps also an object in a distant/slow enough orbit.

Posted by: JTN Jan 6 2006, 12:47 PM

Damntoolate.

Darn, should have enabled stars in Saturn Viewer. Thanks.

Posted by: SigurRosFan Jan 6 2006, 01:30 PM

I did not found this identification. At Calsky I found TYC 4696-972-1.

It is the same star?

Posted by: elakdawalla Jan 6 2006, 07:11 PM

I put together a version of the animation where I tried to keep the rings at a constant vertical position and I also evened out the brightness and contrast and added labels for all of the bodies visible. You can download it here (1 MB, GIF format):

http://www.planetary.org/image/titan_ep_di_pa_mutevent.gif

What would be really cool would be to take colors from true color images of Saturn, the rings, and Titan and apply them as a wash over the frames (Saturn is overexposed so you'd have to fiddle with that a bit more). It'd be a bit tedious to do but would result in a super cool animation. I'd be happy to email the photoshop file I made the GIF animation from to anybody who'd like to take a crack at that

--Emily

Posted by: pat Jan 6 2006, 07:20 PM

Ooops, I've become so used to the catalogue numbers as they appear in the analysis software. I believe the correct "real world" designation is:

TYC 4696-972-1 from the Tycho 2 catalogue (not the Tycho catalogue)

BTmag 8.808
VTmag 7.831

RA(ICRS at J2000 epoch) 34.98304111 deg
dec(ICRS at J2000 epoch) -6.32177417 deg

Hipparchos catalogue number:

HIP 10872

Sorry

Posted by: SigurRosFan Jan 6 2006, 07:49 PM

Thanks. More IDs: http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=HIP+10872&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2006&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0

Posted by: SigurRosFan Jan 8 2006, 12:51 PM

Here's an artless animation:

Nice starfield around HD 14447, Dione and Epimetheus

Photobucket has made a resized version, because the file is too big (1.1 MB).

Animation:


The five bright stars are from left to right: HD 14516 (7.9mag), HD 14504 (9mag), SAO 129835 (9.8mag), HD 14447 (7.7mag) and SAO 129827 (10mag)

Posted by: Tman Jan 10 2006, 10:39 PM

Nice animations, Emily, Nico!

( As you know) my present passion is also to put such Cassini animations in front of the actual starfield, as soon as more than one star appears therein. But this "mutual event" it's too complex (to me) to do the same work like by http://www.unmannedspaceflight.com/index.php?showtopic=1842. So I made only one picture of it, therein Epimetheus and Dione appear three times and...: (530 kb) http://www.greuti.ch/cassini/sat_epi_dione_titan_starfield.jpg

The starfield is rather exact 1 degree and Cassini's NAC shoots of 0,35 degrees fitted therein. So Cassini would see the starfield "likewise" with the accurate exposure time (I guess) - but of course the galaxies not in such resolution.