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"artificial image artifacts" Saturn Equinox (2009 Aug 25)
Posted: Tue Aug 25, 2009 2:18 pm
by cwmdavis
Oh, oh, dirty sensor! Many need to send up the space shuttle for a cleaning ...
http://apod.nasa.gov/apod/ap090825.html
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Tue Aug 25, 2009 2:57 pm
by Aqua
Image artifacts they might be... but might some of them also not possibly be meteor(s) passing thru the ring plane?
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Tue Aug 25, 2009 3:03 pm
by neufer
Aqua wrote:Image artifacts they might be... but might some of them also not possibly be meteor(s) passing thru the ring plane?
Highly unlikely. Blame cosmic rays.
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Tue Aug 25, 2009 4:42 pm
by NoelC
The little streaks are most likely, as Neufer says, particle hits on the imager. One sees a lot of these in Hubble images, especially if the sun is active. Gives one a healthy respect for the protection given us by our wonderful atmosphere.
I'd also like to point out the banding distortion (the horizontal light and dark streaks at a more or less constant frequency)... Those are most definitely not actual light and shadow on Saturn's rings, especially considering the real shadow? near the bottom that's not horizontal.
It is possible to greatly reduce such distortion with digital processing, and it is particularly easy to remove it from an image that has virtually no other horizontal components.
Click on this small image to see a large one.
-Noel
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Thu Aug 27, 2009 2:44 am
by grump
NoelC wrote:The little streaks are most likely, as Neufer says, particle hits on the imager.....
-Noel
And if they are not? Has anyone read "Footfall" by Larry Niven and Jerry Pournelle?
http://en.wikipedia.org/wiki/Footfall
- unserious Jim
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Thu Aug 27, 2009 10:45 am
by geckzilla
I don't understand why the streaks are so crisp. I don't think they are any kind of flying debris but I don't understand why they are in focus, either. Which part is damaged?
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Thu Aug 27, 2009 11:47 am
by zbvhs
Would the image artifacts be stars? If a timed exposure was required to capture the fainter details of the rings, seems like stars should become visible. (Are technical details such as exposure time published with the photographs?)
Has an explanation of the rings' structure been proposed? Why, for example, are the rings perfectly circular? (Are they perfectly circular?) Why are they orbiting in the planet's equatorial plane, i.e., zero inclination? Are they orbiting in the usual sense or is some other mechanism at work? Would gravitational perturbations caused by Saturn's moons be evident in the rings' structure?
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Thu Aug 27, 2009 1:50 pm
by BMAONE23
zbvhs wrote:Would the image artifacts be stars? If a timed exposure was required to capture the fainter details of the rings, seems like stars should become visible. (Are technical details such as exposure time published with the photographs?)
Has an explanation of the rings' structure been proposed? Why, for example, are the rings perfectly circular? (Are they perfectly circular?) Why are they orbiting in the planet's equatorial plane, i.e., zero inclination? Are they orbiting in the usual sense or is some other mechanism at work? Would gravitational perturbations caused by Saturn's moons be evident in the rings' structure?
In reply to your last query about moons within the rings
http://www.nasa.gov/mission_pages/cassi ... 11653.html
More info on the Rings from WIKI
http://en.wikipedia.org/wiki/Rings_of_Saturn
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Thu Aug 27, 2009 2:16 pm
by Chris Peterson
geckzilla wrote:I don't understand why the streaks are so crisp. I don't think they are any kind of flying debris but I don't understand why they are in focus, either. Which part is damaged?
They are classic cosmic ray hits on the CCD. I get them all the time on my images, and the rate is higher in space. Sometimes the high energy particles directly hit the CCD, which usually creates a really messy splash. Most often, they first strike something else, like the CCD chip packaging, surrounding camera structure, etc, and this produces a shower of lower energy particles- one or more of which may strike the sensor. When that happens they can dump a charge into one or more pixels, which shows up as a white point or a white streak. They appear to be in focus because they are affecting the pixels directly, and there is a sharp boundary between affected and unaffected pixels. Of course, there are no optics involved so "focus" really has no meaning.
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Thu Aug 27, 2009 2:21 pm
by Chris Peterson
zbvhs wrote:Would the image artifacts be stars? If a timed exposure was required to capture the fainter details of the rings, seems like stars should become visible. (Are technical details such as exposure time published with the photographs?)
I haven't seen any technical exposure details published. Even edge on, this is still ice illuminated by sunlight, so I expect the exposure was pretty short. That said, there are a few bright spots that might possibly be stars- hard to say without more information about exposure and orientation. But without doubt, most of the artifacts are the product of high energy particles hitting the sensor.
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Fri Aug 28, 2009 10:11 am
by geckzilla
Oh, so it's not like something has physically made an impact and damaged something then. Oops.
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Fri Aug 28, 2009 1:27 pm
by Chris Peterson
geckzilla wrote:Oh, so it's not like something has physically made an impact and damaged something then. Oops.
It's still an "impact" when a high energy particle hits the sensor, and these impacts do occasionally cause permanent damage. CCDs degrade over time because of the cumulative damage of cosmic ray impacts.
Re: "artificial image artifacts" Saturn Equinox (2009 Aug 25
Posted: Sat Aug 29, 2009 10:36 am
by Andy Wade
Thanks Chris, That's really helped my understanding. As always...
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