As I was browsing through the highlights of the extended mission, I noticed that equinox will be in August 2009 (and Cassini will be near periapsis). So far, I'm having a hard time imaging how the rings will appear as the sun sets over the "horizon".
Will the ringlets blend together into a dusky, featureless disk?
Will the spokes stand out?
How would moon shadows play across the expanse?
How would any warping affect the appearance of the rings?
Any thoughts?
Full Version: Rings at equinox
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Ooo...good questions, don't know!
IIRC (and I might not), Cassini's orbit will be back in the equatorial plane at this time (at least it should be if there's no change in inclination after the end of the primary mission). To me, this seems like a good opportunity to look for larger ring particles, the ones that are presumably plowing out the ringlets.
IIRC (and I might not), Cassini's orbit will be back in the equatorial plane at this time (at least it should be if there's no change in inclination after the end of the primary mission). To me, this seems like a good opportunity to look for larger ring particles, the ones that are presumably plowing out the ringlets.
QUOTE (nprev @ Mar 29 2008, 04:58 AM) 
IIRC (and I might not), Cassini's orbit will be back in the equatorial plane at this time (at least it should be if there's no change in inclination after the end of the primary mission). To me, this seems like a good opportunity to look for larger ring particles, the ones that are presumably plowing out the ringlets.
Actually it might be better for Cassini to be in an inclined orbit at the time of equinox. Larger ring particles would be more visible seen from above than from the side.
At the exact time of equinox they would appear as bright dots on the darkened ringplane.
And, in the days just before and after equinox, their shadows on the ringplane ought to be visible.
Besides that, IIRC, when you look at Saturn's rings edge-on what you are really seeing is the F ring. So at equinox the edge-on view might not be much different from what we normally see.
QUOTE (Rob Pinnegar @ Mar 29 2008, 07:44 AM)
Actually it might be better for Cassini to be in an inclined orbit at the time of equinox. Larger ring particles would be more visible seen from above than from the side.
At the exact time of equinox they would appear as bright dots on the darkened ringplane.
And, in the days just before and after equinox, their shadows on the ringplane ought to be visible.
Besides that, IIRC, when you look at Saturn's rings edge-on what you are really seeing is the F ring. So at equinox the edge-on view might not be much different from what we normally see.
At the exact time of equinox they would appear as bright dots on the darkened ringplane.
And, in the days just before and after equinox, their shadows on the ringplane ought to be visible.
Besides that, IIRC, when you look at Saturn's rings edge-on what you are really seeing is the F ring. So at equinox the edge-on view might not be much different from what we normally see.
Being in inclined orbits for 2-3 months on either side of the Equinox date was a prime requirement for the XM from RINGS
One reason being to see how the temeprature changes in the Rings at sunrise and onward.... The dark side of the B-Ring
is *cold* it should heat slowly .... anyway ... the equinox is a time of major interest for RINGS.
We also want to see what topography may exist there that is just not visible at any other time.
I think the Las Vegas oddsmakers place the odds for new moonlets being found really ...really low.
T
Sometimes you'll catch sight of a wall when the sun is nearly in the plane of the wall, and the shadows can be elongated spectacularly. If you consider a shadow as an image of the profile of the wall at some local convexity, you basically get a magnified version of that feature, and as the source gets arbitrarily close to the plane, that magnification becomes arbitrarily more powerful. (Walking down the hill where I live last week, I noticed that my own shadow became over a block long.) In principle, a centimeter-sized pellet could cast a shadow 10,000 km long (of course, only 1 cm wide...).
I don't know if Cassini will produce any imagery bringing that effect out, but my guess is that there'll be something interesting about the off-plane variations in the ring that can be deciphered from a few key images.
The Sun's apparent motion WRT the plane is faster at equinox than at any other time, but with Saturn creaking along at about one degree per month, and the Sun only about 1/30 degree in apparent size, there should be plenty of good photo ops for about four or more days.
I don't know if Cassini will produce any imagery bringing that effect out, but my guess is that there'll be something interesting about the off-plane variations in the ring that can be deciphered from a few key images.
The Sun's apparent motion WRT the plane is faster at equinox than at any other time, but with Saturn creaking along at about one degree per month, and the Sun only about 1/30 degree in apparent size, there should be plenty of good photo ops for about four or more days.
Besides the subtlest topography... Ring Warps, inclined spiral resonance waves, some ring segments may be thicker than others.
But a primary target for zero sun elevation studies will be the ring's "dust atmosphere"... what we think the spokes are and other populations of small levitated particles.
But a primary target for zero sun elevation studies will be the ring's "dust atmosphere"... what we think the spokes are and other populations of small levitated particles.
QUOTE (edstrick @ Mar 30 2008, 06:58 AM)
Besides the subtlest topography... Ring Warps, inclined spiral resonance waves, some ring segments may be thicker than others.
But a primary target for zero sun elevation studies will be the ring's "dust atmosphere"... what we think the spokes are and other populations of small levitated particles.
But a primary target for zero sun elevation studies will be the ring's "dust atmosphere"... what we think the spokes are and other populations of small levitated particles.
Looks like some spokeage on the raw ring images just prior to the T43 Titan images...
Spokeage or flatfield effects? The two dark regions in the rings appear to be static across a huge number of frames.
Looks like spokeage to me...more than 500 images of it! So there must be a pretty high frame rate, which would explain why they look static. I wonder how many images there actually are in this sequence. A pox on whoever decided to take down the option to query the raw images database by time of day, so that you could subset a day when they take more than 500 images per day. Now, if there are more than 500 images, the 500+nth images are not available to the public until they hit the PDS.
They take these movies, IIRC, of the rings where they are emerging from Saturn's shadow so as to try to figure out how the spokes are generated.
--Emily
They take these movies, IIRC, of the rings where they are emerging from Saturn's shadow so as to try to figure out how the spokes are generated.
--Emily
It was a couple thousand images IIRC.
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