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Cassini "Kodak Moments"
helvick
post Mar 4 2007, 07:47 PM
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JTN,

I see your point - if I run things forward though by about 12 hours I get this which must be Titan then, possibly the timing I got for the transit is wrong or there is some issue with Celestia handling dates back in the 19th Century.

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volcanopele
post Mar 4 2007, 07:59 PM
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QUOTE (JTN @ Mar 4 2007, 12:30 PM) *
(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 )
I'm working on a public version of an add-on I've been using that will drastically improve the positions of Cassini and Saturn's moons for the time period of the Cassini mission.


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JTN
post Mar 4 2007, 09:49 PM
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QUOTE (helvick @ Mar 4 2007, 07:47 PM) *
I see your point - if I run things forward though by about 12 hours I get this which must be Titan then, possibly the timing I got for the transit is wrong or there is some issue with Celestia handling dates back in the 19th Century.

I think the times Lord Lindsay gives must be p.m. -- xephem says Saturn would have been below the horizon from the UK at 5:46 a.m. (these observations appear to be from Aberdeen).
(BTW, on p98 there's mention of Titan shadow transit observations on Oct 22 and Nov 23.)
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scalbers
post Mar 11 2007, 05:42 PM
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Greetings,

It appears Helvick has shown that Celestia can render both Titan and at least one smaller satellite in shadow transit. Looking at the case from this month at the appropriate time (Mar 2 1700-1800UT) I was unable to see any shadow transit from Mimas even though it was in front of Saturn as seen in a solar perspective. I used Celestia 1.3.2. The sun centered view also showed Enceladus near that time passing just south of the limb, so it's unclear to me which satellite (Mimas or Enceladus) would have been in more of a position for this type of grazing shadow transit. So I wonder which smaller satellite Helvick was showing and whether Celestia will show shadow transits for satellites as small as Mimas & Enceladus? Perhaps I'll try running Celestia near solar ring plane crossing time and see how the shadow transits look with more regularity.


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scalbers
post Mar 11 2007, 06:03 PM
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I found on the Celestia forum that at least Iapetus can be shown. If I have this link correct, it should show a 1980 shadow transit from Iapetus where its shadow falls within the rings' shadow. This version of Celestia would not however show Iapetus' shadow on the rings itself. The inclination of Iapetus means its shadow can be less elongated on the rings. I wonder if there will be a similar event in the coming 2009 season?

http://www.lns.cornell.edu/~seb/celestia/gallery-001.html#5a


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volcanopele
post Mar 11 2007, 06:03 PM
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Here is what I was able to get with Celestia 1.5pre2:

Tethys transit (2009-03-16)
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I couldn't see Mimas or Enceladus...


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helvick
post Mar 11 2007, 06:37 PM
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Scalbers - I used Celestia 1.5 pre release for the screen caps I posted but I also am unable to find the March 2 Mimas shadow so I don't think the newer version is the reason we can't see it. By my calculations the umbral shadow will only be around 60km across so it will be hard to find unless you know precisely where to look and can zoom in appropriately. I'm pretty sure the shadow will be rendered if the zoom level is sufficient but catching it is beyond me at the moment.

This may have been noted before but I found out that the Ciclops team used Celestia to render the views for the Rev 29 lookahead page while looking for more information on the eclipse shadow rendering.
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volcanopele
post Mar 11 2007, 06:43 PM
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Yeah, although I have discovered a bug in my custom .ssc file that means that the Titan map isn't displayed correctly on Titan. I think the rotation offset is off, but it is odd to characterize.


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jsheff
post Mar 12 2007, 07:19 PM
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JTN,

I agree with you. Starry Night shows the Titan transit at 17:53:00 UT on Dec. 25, almost exactly 12 hours later than Lord Lindsay states.

John Sheff
Cambridge, MA
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CAP-Team
post Mar 19 2007, 06:40 PM
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Same image, but now generated with xplanet:

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Toma B
post Mar 20 2007, 05:37 PM
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There are 3 new Saturn animations on HST site. Some old transits animated...nice.


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ngunn
post Mar 20 2007, 06:05 PM
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Very nice animations, but the captions for 1 and 3 appear to have been swapped.
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As old as Voyage...
post Mar 20 2007, 07:10 PM
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December 2000 seems an awfully long time ago.

http://photojournal.jpl.nasa.gov/catalog/PIA08899


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HughFromAlice
post Jul 8 2008, 08:58 PM
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Check out video of Carloyn Porco at 8th July New Scientist talking about her favourite images of the Cassini primary mission. http://space.newscientist.com/article/dn14...ini-images.html

Even though you may have seen these images before it's fascinating to hear what makes them her favourites.

For me - the hi phase shot of the crescent of Titan is something special. The last pic of a back lit Saturn with an eclipsed sun peaking out on the edge of the disc with a clear view of the G ring and E (Enceladus jet created) ring and the blue orb of the earth at 10 o'clock next to the G ring is awe inspiring.
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CAP-Team
post Jul 20 2008, 09:39 PM
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I was playing with Celestia to find out when Titan's shadow will be passing Saturn when the rings are nearly edge on, so Titan's shadow is bigger than the ring's shadow. Or, better said, when Titan's shadow will fall directly on the rings, which should be a weird sighting.

Unfortunately Celestia can't cast the shadow of Titan on the rings itself, but Titan's passage on 2/3 august should be spectacular! At this time (around 5 am UTC) Cassini will be able to watch Titan's shadow cross the rings from a distance of about 2 million kilometers (phase angle of Saturn is 113 degrees).

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