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The Grand Finale, Proximal orbits
wildespace
post Apr 28 2017, 03:01 AM
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QUOTE (B Bernatchez @ Apr 27 2017, 05:40 PM) *
Excuse my ignorance, but this hurricane is the one at the North Pole, right?

Yes.

The south pole is currently in the shadows (saturnian winter) and looks like this:

Attached Image


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avisolo
post Apr 28 2017, 09:17 AM
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I made a gif of the dive!
http://i.imgur.com/i6uMzG2.gifv
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wildespace
post Apr 29 2017, 09:46 AM
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Nice colours in this recent view (RGB stack from W00107043, W00107044 and W00107045)

Attached Image


Although I'm not quite sure what we're looking at here. Night side of Saturn with some inner rings?


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Astroboy
post Apr 29 2017, 11:46 PM
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Enceladus spraying away on April 27. Reminds me a lot of the Io volcano footage from Voyager 2.



EDIT: I didn't realize there would be more to this observation! D'oh!
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MichaelJWP
post May 4 2017, 10:20 AM
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Not sure if this has been posted, but this movie puts the images in context nicely:

NASA: Cassini's First Fantastic Dive Past Saturn

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Phil Stooke
post May 4 2017, 01:47 PM
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Wildespace said, just above:

"Nice colours in this recent view (RGB stack from W00107043, W00107044 and W00107045)

Although I'm not quite sure what we're looking at here. Night side of Saturn with some inner rings?"


I think probably the outer rings, E at the top and G in the middle in forward-scattered light, with the limb of Saturn below, and a long exposure.

Phil


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Ian R
post May 4 2017, 03:41 PM
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We're looking at the south pole of Saturn (currently in mid-winter darkness), and the G and E rings. In the background is a star field which straddles the Orion / Taurus border:

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http://nova.astrometry.net/user_images/1609771#original


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scalbers
post May 4 2017, 04:07 PM
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Interesting brightness changes on the limb. Is this Saturnian twilight modulated by ring shadows?


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ngunn
post May 9 2017, 01:21 PM
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With much of the attention on Saturn and the rings, Titan has decided to put on an extra special clouds performance: https://saturnraw.jpl.nasa.gov/multimedia/i...9/N00281060.jpg
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tanjent
post May 10 2017, 12:17 AM
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The background writeup for the cloud picture.
https://saturn.jpl.nasa.gov/resources/7673/
It's good to know that the spacecraft is still able to monitor events at Titan, even with no more close passes scheduled.
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JRehling
post May 10 2017, 03:42 PM
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QUOTE (scalbers @ May 4 2017, 09:07 AM) *
Interesting brightness changes on the limb. Is this Saturnian twilight modulated by ring shadows?


The rings do indeed partially block sunlight from reaching the southern border of what would otherwise be the southern boundary of daylight / seasonal darkness. This is suggested by current telescope views of Saturn as seen from Earth and I just confirmed it with the Solar System Simulator's view of Saturn as seen from the Sun. The SSS view of Saturn as seen from below (attached) shows a U-shape, which matches your intuition. Cassini is seeing the tips of the U in a twilight time of day.

Thank goodness for the simulator, because it would take pages of trigonometry to work that out from first principles.

An interesting consequence is that an observer at the right latitude in Saturn's clouds would see two periods of daylight during this season – morning and afternoon – with a couple hours of "night" during the solar eclipse-by-the-rings around noon.

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scalbers
post May 10 2017, 11:05 PM
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Thanks JRehling for that informative discussion with the simulated view. In that I can note an inner U and an outer U. Perhaps we're seeing more of the inner U in the Cassini image, and this U is from the sunlight coming through the Cassini division? The center of the limb is thus shadowed by the A ring and the limb edges (in the image) show sunlight coming through the Cassini division.

As seen from the Sun (and Earth) the outer edge of the A ring thus completely misses the planet while the Cassini Division continues to intersect the planetary ellipsoid. We are really close to the widest open possible with the summer solstice coming up May 24. It then follows that light passing through the Cassini Division would never hit the terminator point nearest the pole.


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JRehling
post May 11 2017, 02:44 AM
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I puzzled over the geometry for a while, trying to simulate, in Photoshop, what the planet looks like behind the rings when it occurred to me that the summer and winter geometries are similar, and the parts of the rings that do and don't cast a shadow on the winter pole are exactly symmetrical with the parts of the rings that do and don't have the planet's shadow cast on them on the summer pole. I've attached an image of Saturn that I took on April 15, which is close to the current situation.

The inner edge of the A ring is slightly in the planet's shadow behind the north pole, but the outer edge is not, so the same situation will apply in the south, where it's harder to visualize what's going on. The Cassini Division will paint a curvy stripe of light on the planet near the winter pole, and that's the inner "U" in the view from below.


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Ian R
post May 13 2017, 12:26 AM
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Soon ..... cool.gif

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jasedm
post May 14 2017, 08:00 PM
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Nice image from 1st May - Sirius (bleaching out dozens of pixels in the camera) just about to be occulted by the F-ring.

I love the little bonus of Pandora photobombing the shot just to the left.

Still a mission full of unexpected delights.

smile.gif

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