Explanation: You couldn't really be caught in this blizzard while standing by a cliff on Churyumov-Gerasimenko, also known as comet 67P. Orbiting the comet in June of 2016 the Rosetta spacecraft's narrow angle camera did record streaks of dust and ice particles though, as they drifted across the field of view near the camera and above the comet's surface. Still, some of the bright specks in the scene are likely due to a rain of energetic charged particles or cosmic rays hitting the camera, and the dense background of stars in the direction of the constellation Canis Major. Click on this single frame to play and the background stars are easy to spot as they trail from top to bottom in an animated gif (7.7MB). The 33 frames of the time compressed animation span about 25 minutes of real time. The stunning gif was constructed from consecutive images taken while Rosetta cruised some 13 kilometers from the comet's nucleus.
Do the charged particles/cosmic rays only strike the camera ccd with the shutter open, or do they continue regardless. ?
(Which may not be immediately obvious, since with the shutter closed it may not be recording anything )
And, on a similar theme, didn't the astronauts en route to the moon (lunarnauts ?) etc report that they had noted a continuous series of flashes in their eyes, even when they were sleeping. Something voyagers to Mars may need some consideration of......
RocketRon wrote: ↑Thu Apr 26, 2018 5:48 am
Do the charged particles/cosmic rays only strike the camera ccd with the shutter open, or do they continue regardless. ?
(Which may not be immediately obvious, since with the shutter closed it may not be recording anything )
Always. They strike the sensor from all directions, arriving not just from the side of the lens but even behind. Depending on the sensor type, it may well be "recording" all the time, meaning that it's collecting signal. But often this will not be stored; the charge on the sensor is cleared before starting an actual exposure. However, this is not the case for a special kind of calibration image called a dark frame. It's made with the shutter closed, in order to capture certain artifacts that are inherent in the sensor so that they can be subtracted out of the final science image. However, when you have cosmic ray hits on your dark frame, your calibration process then transfers them to any frames processed with that image.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
RocketRon wrote: ↑Thu Apr 26, 2018 5:48 am
Do the charged particles/cosmic rays only strike the camera ccd with the shutter open, or do they continue regardless. ?
(Which may not be immediately obvious, since with the shutter closed it may not be recording anything )
Always. They strike the sensor from all directions, arriving not just from the side of the lens but even behind. Depending on the sensor type, it may well be "recording" all the time, meaning that it's collecting signal. But often this will not be stored; the charge on the sensor is cleared before starting an actual exposure. However, this is not the case for a special kind of calibration image called a dark frame. It's made with the shutter closed, in order to capture certain artifacts that are inherent in the sensor so that they can be subtracted out of the final science image. However, when you have cosmic ray hits on your dark frame, your calibration process then transfers them to any frames processed with that image.
I think that a second imaging instrument (camera) to provide 'binocular vision' would be helpful. Cosmic rays will only be able to strike one of the imaging surfaces, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other camera would have been inconsequential with respect to the cost of the mission, and the science value would be great. It is still a great video effort, tho some scale would have been nice to have. I wonder how cold it is?
RocketRon wrote: ↑Thu Apr 26, 2018 5:48 am
Do the charged particles/cosmic rays only strike the camera ccd with the shutter open, or do they continue regardless. ?
(Which may not be immediately obvious, since with the shutter closed it may not be recording anything )
Always. They strike the sensor from all directions, arriving not just from the side of the lens but even behind. Depending on the sensor type, it may well be "recording" all the time, meaning that it's collecting signal. But often this will not be stored; the charge on the sensor is cleared before starting an actual exposure. However, this is not the case for a special kind of calibration image called a dark frame. It's made with the shutter closed, in order to capture certain artifacts that are inherent in the sensor so that they can be subtracted out of the final science image. However, when you have cosmic ray hits on your dark frame, your calibration process then transfers them to any frames processed with that image.
I think that a second imaging instrument (camera) to provide 'binocular vision' would be helpful. Cosmic rays will only be able to strike one of the imaging surfaces, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other camera would have been inconsequential with respect to the cost of the mission, and the science value would be great. It is still a great video effort, tho some scale would have been nice to have. I wonder how cold it is?
In fact, adding a second camera could easily have elevated the cost of the mission by tens of millions of dollars, and would have demanded either a different power system or the loss of some other instrument. Every watt is allocated in probes like this. Cosmic ray hits on sensors are rarely a serious problem, as they can be removed in almost all cases and have minimal impact on the science.
When 67P was at this distance from the Sun, its surface temperature was about 200 K, give or take about 20 K depending on surface location. Say, -70° C. A cold day in Siberia or Antarctica.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
Guest wrote: ↑Thu Apr 26, 2018 1:44 pm
I think that a second imaging instrument (camera) to provide 'binocular vision' would be helpful. Cosmic rays will only be able to strike one of the imaging surfaces, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other camera would have been inconsequential with respect to the cost of the mission, and the science value would be great. It is still a great video effort, tho some scale would have been nice to have. I wonder how cold it is?
In fact, adding a second camera could easily have elevated the cost of the mission by tens of millions of dollars, and would have demanded either a different power system or the loss of some other instrument. Every watt is allocated in probes like this. Cosmic ray hits on sensors are rarely a serious problem, as they can be removed in almost all cases and have minimal impact on the science.
There are 3 cameras effectively considering the images taken just before or just after.
(And a backup camera provides less insurance that would a backup reaction wheel for pointing.)
Chris Peterson wrote: ↑Thu Apr 26, 2018 1:54 pm
When 67P was at this distance from the Sun, its surface temperature was about 200 K, give or take about 20 K depending on surface location.
Say, -70° C. A cold day in Siberia or Antarctica.
"And it ain't a fit night out for man or beast!"
"Kilimanjaro is a snow-covered mountain 19,710 feet high, and is said to be the highest mountain in Africa. Its western summit is called the Masai "Ngaje Ngai," the House of God. Close to the western summit there is the dried and frozen carcass of a leopard. No one has explained what the leopard was seeking at that altitude."
Guest wrote: ↑Thu Apr 26, 2018 1:44 pm
I think that a second imaging instrument (camera) to provide 'binocular vision' would be helpful. Cosmic rays will only be able to strike one of the imaging surfaces, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other camera would have been inconsequential with respect to the cost of the mission, and the science value would be great. It is still a great video effort, tho some scale would have been nice to have. I wonder how cold it is?
In fact, adding a second camera could easily have elevated the cost of the mission by tens of millions of dollars, and would have demanded either a different power system or the loss of some other instrument. Every watt is allocated in probes like this. Cosmic ray hits on sensors are rarely a serious problem, as they can be removed in almost all cases and have minimal impact on the science.
There are 3 cameras effectively considering the images taken just before or just after.
Exactly, and that's why transient artifacts are usually not a problem. It is only with highly transient targets that it can be problematic, but those are rare in astronomical applications. Even in something like the source data for this image. I heard a talk at a conference a couple of years ago by a team that had used this type of imagery to track individual dust and ice grains produced by the comet. Since these were short frames taken in close duration, there was no simple way to isolate cosmic ray hits from dust. But with more complex analysis, individual grains could be correlated between frames (even though they moved), whereas cosmic ray hits could not.
Close to the western summit there is the dried and frozen carcass of a leopard. No one has explained what the leopard was seeking at that altitude.
Enlightenment?
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
Chris Peterson wrote: ↑Thu Apr 26, 2018 1:54 pm
In fact, adding a second camera could easily have elevated the cost of the mission by tens of millions of dollars, and would have demanded either a different power system or the loss of some other instrument. Every watt is allocated in probes like this. Cosmic ray hits on sensors are rarely a serious problem, as they can be removed in almost all cases and have minimal impact on the science.
There are 3 cameras effectively considering the images taken just before or just after.
Exactly, and that's why transient artifacts are usually not a problem.
It is only with highly transient targets that it can be problematic, but those are rare in astronomical applications.
<<In practice, the community of scientists concerned with finding life elsewhere in the solar system has contented itself with a chemical approach. Human beings, as well as every other organism on the earth, are based on liquid water and organic molecules. (Organic molecules are carbon-containing compounds other than carbon dioxide and carbon monoxide.) A modest search strategy--looking for necessary if not sufficient criteria--might then begin by looking for liquid water and organic molecules. Of course, such a protocol might miss forms of life about which we are wholly ignorant, but that does not mean we could not detect them by other methods.
If a silicon-based giraffe had walked by the Viking Mars landers, its portrait would have been taken.>>
neufer wrote: ↑Thu Apr 26, 2018 2:47 pm
Close to the western summit there is the dried and frozen carcass of a leopard. No one has explained what the leopard was seeking at that altitude.
<<Ernest Hemingway opens his 1936 short story "The Snows of Kilimanjaro" by mentioning a leopard carcass up near the summit of Mount Kilimanjaro, at 19,341 feet the tallest mountain in Africa: "Close to the western summit there is the dried and frozen carcass of a leopard. No one has explained what the leopard was seeking at that altitude."
The short story may be a piece of fiction, but Hemingway's reference isn't. In 1926, a Lutheran pastor named Richard Reusch, who made multiple climbs up Kilimanjaro, did indeed discover a "freeze-dried" leopard at roughly 18,500 feet along the crater rim of the volcano's loftiest sub-peak, Kibo. A photo of the find shows the dead animal looking about as you'd expect after chilling (so to speak) on a mountaintop snowfield for who knows how long.
Reusch suspected the leopard had died in pursuit of a goat, the remains of which he also found a few hundred feet away. Returning to the contorted mummy the next year, Reusch lopped off an ear for souvenir purposes. At some point or another, the corpse disappeared, but given the Hemingway shout-out, it's about as immortalised as a popsicled wild animal could be. (The general location of the carcass now holds the unofficial label of "Leopard Point".)>>
Chris Peterson wrote: ↑Thu Apr 26, 2018 1:54 pm
Cosmic ray hits on sensors are rarely a serious problem, as they can be removed in almost all cases and have minimal impact on the science.
So are you saying that the prominent "snow" in these images is entirely real reflections from physical particles in the field of view, and not an artifact of noise created by interactions of stray high-energy photons or particles directly impinging the sensor?
Note that the images were from 13Kms away. Two (or three) cameras would have needed to be some distance apart.
Curiosity's navigation cams can be used to make anaglyph pics https://www.smithsonianmag.com/smart-ne ... -25880779/ but the further away the object, the less impressive is the result.
Chris Peterson wrote: ↑Thu Apr 26, 2018 1:54 pm
Cosmic ray hits on sensors are rarely a serious problem, as they can be removed in almost all cases and have minimal impact on the science.
So are you saying that the prominent "snow" in these images is entirely real reflections from physical particles in the field of view, and not an artifact of noise created by interactions of stray high-energy photons or particles directly impinging the sensor?
Most of the "snow" is either particles of dust or ice, or background stars. But this isn't a science image. Cosmic rays could be largely isolated and removed by comparing images in the sequence used to produce this animation.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
<<Tauntauns are 2.5 m tall bipedal reptiles, indigenous to the ice planet Hoth. Tauntauns are covered with white fur and have downturned horns, four nostrils, and a foul body odor. They subsist off lichen found in hoarfrost as well as eating mushrooms and other fungi found in ice caves. They give birth to two young at a time, twice in one Hoth year, although triplet Tauntauns are considered incredibly good luck and are often born with purple fur. They are used as mounts by the Rebel Alliance, and have been exported offworld to other cold-climate regions (including Coruscant's polar caps) for use as mounts, beasts of burden, and tourist attractions. Their thick layers of fat and fur provide adequate protection from the cold during the daytime, but tauntauns cannot survive the plummeting night temperatures without shelter. Tauntauns are sometimes preyed upon by the Wampa.>>
<<Tauntauns are 2.5 m tall bipedal reptiles, indigenous to the ice planet Hoth. Tauntauns are covered with white fur and have downturned horns, four nostrils, and a foul body odor. They subsist off lichen found in hoarfrost as well as eating mushrooms and other fungi found in ice caves. They give birth to two young at a time, twice in one Hoth year, although triplet Tauntauns are considered incredibly good luck and are often born with purple fur. They are used as mounts by the Rebel Alliance, and have been exported offworld to other cold-climate regions (including Coruscant's polar caps) for use as mounts, beasts of burden, and tourist attractions. Their thick layers of fat and fur provide adequate protection from the cold during the daytime, but tauntauns cannot survive the plummeting night temperatures without shelter. Tauntauns are sometimes preyed upon by the Wampa.>>
When John Glenn was orbiting the Earth in his Mercury capsule, he reported a similar phemomenon, a cloud of bright white snowflake-like, star-like objects around the capsule. Could that have been something like what we're seeing here?
kevinmcc29 wrote: ↑Thu Apr 26, 2018 7:23 pm
When John Glenn was orbiting the Earth in his Mercury capsule, he reported a similar phemomenon, a cloud of bright white snowflake-like, star-like objects around the capsule. Could that have been something like what we're seeing here?
I think that a second imaging instrument (eyeball) to provide 'binocular vision' would have been helpful. Cosmic rays will only be able to strike one of the eyeballs, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other eyeball would have been inconsequential with respect to the cost of the mission, and the science value would be great.
The Snows of Churyumov-Gerasimenko
