IPB

Welcome Guest ( Log In | Register )

2 Pages V   1 2 >  
Reply to this topicStart new topic
The unlit side of the rings
Bjorn Jonsson
post Jul 27 2006, 10:56 AM
Post #1


IMG to PNG GOD
****

Group: Moderator
Posts: 1478
Joined: 19-February 04
From: Near fire and ice
Member No.: 38



Cassini has previously imaged the unlit side of the rings but now it is doing extensive observations of the unlit side. For the first time in its mission Cassini is spending a significant amount of time north of the ringplane - earlier it has done so only near periapsis but this orbit is different.

This is a quick RGB composite I did from wide angle images:

Attached Image


I made no attempts to correct the color - this is probably not very far from the true color of the rings. Large color variations are apparent, the C ring and the Cassini division appear much more bluish than the thicker rings (A and B ). It should be noted that these images were very probably downliked with the 12 -> 8 bit encoding which basically means that dark areas appear too bright in this image because I did not correct for this.

It's also interesting to compare this image to Voyager images:

Voyager 1: http://photojournal.jpl.nasa.gov/catalog/PIA02241

Voyager 2: http://photojournal.jpl.nasa.gov/catalog/PIA01955
Voyager 2: http://photojournal.jpl.nasa.gov/catalog/PIA01389
Go to the top of the page
 
+Quote Post
ugordan
post Jul 27 2006, 11:30 AM
Post #2


Senior Member
****

Group: Members
Posts: 3559
Joined: 1-October 05
From: Croatia
Member No.: 523



Great composite. I think it's a tad on the too-blue side, but still it's very neat. Apart from the C ring and the Cassini division, the F ring is also notably blue - it shows nicely in your composite. It's a shame the raws were lossy compressed, otherwise this would make for a very crisp image. Good to see the rings again, even from above.


--------------------
Go to the top of the page
 
+Quote Post
ynyralmaen
post Jul 27 2006, 12:28 PM
Post #3


Member
***

Group: Members
Posts: 108
Joined: 18-July 05
Member No.: 438



Beautiful... one really nice effect that's visible is the "terminator" coincident with Saturn's equator. The atmosphere south of the equator is strongly illuminated by ringshine, but the northern hemisphere significantly less so - neat!
Go to the top of the page
 
+Quote Post
tasp
post Jul 27 2006, 01:41 PM
Post #4


Member
***

Group: Members
Posts: 885
Joined: 30-January 05
Member No.: 162



I recall viewing pictures sent back by Pioneer 11 showing the unlit side of the rings.

It had never occured to me the sun only shown on one side at a time and it was pretty confusing.


I would like to think my general level of comprehension of this stuff has improved a bit . . . .




blink.gif
Go to the top of the page
 
+Quote Post
Bjorn Jonsson
post Jul 29 2006, 12:57 AM
Post #5


IMG to PNG GOD
****

Group: Moderator
Posts: 1478
Joined: 19-February 04
From: Near fire and ice
Member No.: 38



Cassini's view of the unlit side of the rings is remarkably different from the one provided by Voyager 1 back in 1980:

Attached Image


This 'image' is based on intensity scans of Voyager 1 images (top) and Cassini images. The C ring is at left and the F ring at right. The Voyager 1 intensity scan has been corrected for radial distortion so ring features are at their correct relative locations. The Cassini intensity scan is rather crude and has not been corrected so there is some radial distortion, especially in the outer parts of the ring system (the location of major ring features has not changed). Also, since it is based on the JPG versions of the images, exact relative intensity differences are highly uncertain. Despite this it is obvious that there are large differences between the Voyager 1 and Cassini images. In the Voyager 1 images the C ring and the Cassini division appeared brightest whereas in the Cassini images the outer edge of the A ring is brightest with the Cassini division appearing rather dark and the inner part of the B ring appearing quite bright.

The differences in viewing geometry are that the Voyager 1 images were obtained at low phase angle and a low solar elevation angle. In contrast, for the Cassini images the solar elevation angle is high and the phase angle also high.

Interestingly, the Voyager 2 images of the unlit side appear somewhat similar to the recent Cassini images.

The highly varying appearance of the rings as a function of various geometric factors (phase angle, solar elevation angle etc.) is remarkable.
Go to the top of the page
 
+Quote Post
alan
post Jul 29 2006, 07:45 AM
Post #6


Senior Member
****

Group: Members
Posts: 1628
Joined: 20-November 04
From: Iowa
Member No.: 110



Speaking of high phase angles, according to Solar System Simulator on September 15 Cassini will be pass through Saturn's shadow while at a distance of 2.163 million miles.
http://space.jpl.nasa.gov/cgi-bin/wspace?t...=1&showsc=1
I wonder what observations are planned for this.
Go to the top of the page
 
+Quote Post
ugordan
post Jul 29 2006, 10:30 AM
Post #7


Senior Member
****

Group: Members
Posts: 3559
Joined: 1-October 05
From: Croatia
Member No.: 523



QUOTE (alan @ Jul 29 2006, 08:45 AM) *
I wonder what observations are planned for this.

From an imaging standpoint, it looks like a very nice opportunity for a wide angle mosaic. 3 footprints ought to cover the width of the scene so it wouldn't be too expensive to acquire a multicolor set.
Earth should be visible as well -- if it's not drowned out by forward scattered light from the rings. This will be a very high phase angle situation so it's possible the E and G rings will stand out very nicely. The main rings (at least the C and F rings) might be brilliant as well.
Looking forward to it.


--------------------
Go to the top of the page
 
+Quote Post
Bjorn Jonsson
post Jul 29 2006, 07:53 PM
Post #8


IMG to PNG GOD
****

Group: Moderator
Posts: 1478
Joined: 19-February 04
From: Near fire and ice
Member No.: 38



The occultation lasts about 15 hours so there should be plenty of time to point the RSP towards Saturn without accidentally pointing it at the Sun. Sure looks like an interesting imaging opportunity.

The following animation showing the occultation starts at 2006-09-15 03:00:00 UTC and spans a period of 24 hours. The field of view is 8 degrees.

Attached File  sun_occult.avi ( 1.3MB ) Number of downloads: 275
Go to the top of the page
 
+Quote Post
djellison
post Jul 29 2006, 08:40 PM
Post #9


Administrator
****

Group: Chairman
Posts: 13708
Joined: 8-February 04
Member No.: 1



Don't they use these sorts of obs for occultation measurements - VIMS I'd have thought would do well with it - or is there a large 'keep out' for instrument pointing around the sun.

Doug
Go to the top of the page
 
+Quote Post
ugordan
post Jul 29 2006, 09:12 PM
Post #10


Senior Member
****

Group: Members
Posts: 3559
Joined: 1-October 05
From: Croatia
Member No.: 523



True, both VIMS and UVIS can stare at the sun. When these sorts of observations are planned precautions can be taken -- such as disabling the ISS subsystem. Accidental sun exposure could be dangerous to ISS cameras if they were in the middle of a planned imaging sequence and the shutter opened, allowing the sun to burn the CCDs.


--------------------
Go to the top of the page
 
+Quote Post
tallbear
post Jul 30 2006, 01:02 AM
Post #11


Junior Member
**

Group: Members
Posts: 45
Joined: 30-November 05
Member No.: 592



I wonder what observations are planned for this.
[/quote]

There are a number of ORS observations of the entire Ring system at this
very high phase viewing opportunity ... and even a high phase set of
observations of Saturn

There is also an RSS Occ observation of the Rings and Saturn
and a Solar Ring Occ observation as well.

In addition, the RSS 'beam' will pass within 10's of km of Enceladus' S Pole
but with DSS 63 down this will only be observed with Ka band
Go to the top of the page
 
+Quote Post
alan
post Aug 1 2006, 01:57 AM
Post #12


Senior Member
****

Group: Members
Posts: 1628
Joined: 20-November 04
From: Iowa
Member No.: 110



The rings about a quarter of the way up form the bottom of this image look distorted.

http://saturn.jpl.nasa.gov/multimedia/imag...2/N00064487.jpg
Go to the top of the page
 
+Quote Post
dilo
post Aug 1 2006, 05:38 AM
Post #13


Senior Member
****

Group: Members
Posts: 2492
Joined: 15-January 05
From: center Italy
Member No.: 150



Alan, I cannot see the distorsion... exactly, which rings and how they are distorted?

PS: thanks for great unlit side view and the beeatiful animation, Bjorn!


--------------------
I always think before posting! - Marco -
Go to the top of the page
 
+Quote Post
helvick
post Aug 1 2006, 06:04 AM
Post #14


Dublin Correspondent
****

Group: Admin
Posts: 1795
Joined: 28-March 05
From: Celbridge, Ireland
Member No.: 220



QUOTE (dilo @ Aug 1 2006, 06:38 AM) *
Alan, I cannot see the distorsion... exactly, which rings and how they are distorted?

I can see it but to me it looks as if the rings have quite a rough texture - it's almost as if they were drawn by someone with a fairly heavy brush action.
Go to the top of the page
 
+Quote Post
dilo
post Aug 1 2006, 08:27 AM
Post #15


Senior Member
****

Group: Members
Posts: 2492
Joined: 15-January 05
From: center Italy
Member No.: 150



QUOTE (helvick @ Aug 1 2006, 06:04 AM) *
I can see it but to me it looks as if the rings have quite a rough texture - it's almost as if they were drawn by someone with a fairly heavy brush action.

Perhaps you're referring to the disuniformities visible as small hue variation is this RGB version (with enhanced saturation):
Attached Image
(start images N00064483/84/86)
Anyway, is something barely visible to me...

EDIT: just posted a short movie showing spokes transit in this region during previous day, the rough texture noted by alan seems to co-rotate with spokes...


I made the following mosaic of 3 images showing the A/F rings with Saturn shadow:
Attached Image
(start images N00064408/09/17)
I like it...

Finally, did someone noticed this very odd image?
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80270
Image explainations refers to "SATURN-ERING" but I suspect that this bright strip is another piece of main rings, partially eclipsed by saturn shape + shadow... other ideas?


--------------------
I always think before posting! - Marco -
Go to the top of the page
 
+Quote Post

2 Pages V   1 2 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 31st July 2014 - 05:36 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.