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MER-B Dimes images
In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? I had thought the sunlight incidence angle was lower since it is supposed to be around 2PM local time at Meridiani. This seems to be directly below the spacecraft as it descends. So maybe it is something else. The 3 DIMES images are at: http://marsrovers.jpl.nasa.gov/galle...20040125b/MER- B_DIMES_1404m-B22R3.jpg http://marsrovers.jpl.nasa.gov/galle...20040125b/MER- B_DIMES_1690m-B22R3.jpg http://marsrovers.jpl.nasa.gov/galle...20040125b/MER- B_DIMES_1986m-B22R3.jpg Mark |
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MER-B Dimes images
Mark asks:
In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? JPL says that it's the shadow of the parachute. The bright ring around the shadow is of course caused by the diffraction of sunlight around the parachute. Wirt Atmar |
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MER-B Dimes images
mlm writes:
In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? Highly unlikely, since this photo is almost certainly being taken from a quite high altitude, and your alleged "shadow" is a substantial fraction of the large crater's diameter --- whereas even the lander's parachute is quite small compared to the diameter of a typical aregraphical feature !!! Downloading the image and tweaking the image's intensity curve using the image editing tool 'xv' clearly brings out an ejecta blanket surrounding your dark spot, and gradations in intensity within said spot, that strongly suggest to me that your "shadow" is merely a deep, relatively "fresh" crater, and that the limited contrast range of a typical color monitor simply can't easily display the full dynamic contrast range in this image. Once this image has been processed a bit to "dodge out" the "over-exposed" crater rim and "burn in" the darker regions away from the main crater and within the dark, deep crater you've noticed, this picture will become MUCH more photogenic, and the nature of its various features quite obvious. -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
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MER-B Dimes images
In sci.astro Wirt Atmar wrote on 26 Jan 2004 22:49:46 GMT:
:WA Mark asks: In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? :WA JPL says that it's the shadow of the parachute. The bright ring around the :WA shadow is of course caused by the diffraction of sunlight around the parachute. Yes, that is the shadow of the parachute/spacecraft, but the bright halo around it is caused by the opposition affect, not by diffraction of sunlight around the parachute. It is the backscattering of sunlight near the zero phase angle that can also be seen in the abnormal brightening of asteroids near opposition, or even of the full moon. The full moon, for example, is much more than twice as bright as the first quarter moon appears. You can also see the same affect from an airplane if you look on the ground opposite the sun where the shadow of the plane should be - you'll see a bright area on the ground. Jim. Jim Scotti Lunar & Planetary Laboratory University of Arizona Tucson, AZ 85721 USA http://www.lpl.arizona.edu/~jscotti/ |
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MER-B Dimes images
mlm wrote in message ...
In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? I had thought the sunlight incidence angle was lower since it is supposed to be around 2PM local time at Meridiani. This seems to be directly below the spacecraft as it descends. So maybe it is something else. The 3 DIMES images are at: http://marsrovers.jpl.nasa.gov/galle...20040125b/MER- B_DIMES_1404m-B22R3.jpg http://marsrovers.jpl.nasa.gov/galle...20040125b/MER- B_DIMES_1690m-B22R3.jpg http://marsrovers.jpl.nasa.gov/galle...20040125b/MER- B_DIMES_1986m-B22R3.jpg Mark I think it is. Interestingly on the first of 3 DIMES in the lower right quadrant you can see a black dot/line. This looks suspiciously like the heatshield as seen on DIMES image from Spirit. Oh hell why not speculate even more. My bet is that it the lander is in one of the two craters down to the lower left of the larger crater that are side by next vertically in the image. There's not a lot more that I would call candidates. By the way I also think you can see a dimmer version of the shadow in the second DIMES image. RN |
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MER-B Dimes images
On Mon, 26 Jan 2004 08:00:42 -0600, mlm wrote:
In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? I had thought the sunlight incidence angle was lower since it is supposed to be around 2PM local time at Meridiani. This seems to be directly below the spacecraft as it descends. So maybe it is something else. They said in the press conference it's the shadow of the parachute. Bill Cherepy Grayson, GA |
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MER-B Dimes images
mlm wrote:
In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, snip Can you, or anyone, explain the bright ring? It does not seem to cross from the inside to the outside at the 2 points where the solar rays would be tangent to the ridgeline. It looks as if it is lit from the outside all the way around. Mitchell Timin -- "Many are stubborn in pursuit of the path they have chosen, few in pursuit of the goal." - Friedrich Nietzsche http://annevolve.sourceforge.net is what I'm into nowadays. Humans may write to me at this address: zenguy at shaw dot ca |
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MER-B Dimes images
Gordon D. Pusch wrote:
:WA Mark asks: In 1 of the 3 DIMES images taken by Opportunity on its approach to the surface (at 1404m), there is a brightly ringed crater and a distinct, slightly diffuse dark circular shadow about half a crater width to its left. Is this the shadow of the spacecraft? Highly unlikely, since this photo is almost certainly being taken from a quite high altitude, and your alleged "shadow" is a substantial fraction of the large crater's diameter --- whereas even the lander's parachute is quite small compared to the diameter of a typical aregraphical feature !!! He isn't referring to the large dark area on the crater floor. He is refering to a small dark dot with a diffuse bright area around it which sits just to the lower left of the bright rim of the large crater (see the following image: http://marsrovers.jpl.nasa.gov/galle...m-B22R3_br.jpg I believe that it may indeed be the shadow of the parachute and spacecraft since the chute is quite large (somewhere around 17 or 18 meters in diameter) and the altitude is only 1404 meters. It can also be vaguely glimsed in the two other images which were taken at somewhat higher altitudes. The area around the dark dot is lighter, which is consistent with it being a shadow when viewed from above with light backscattered from the surface of Mars in the area immediately around the shadow. Clear skies to you. -- David W. Knisely Prairie Astronomy Club: http://www.prairieastronomyclub.org Hyde Memorial Observatory: http://www.hydeobservatory.info/ ********************************************** * Attend the 11th Annual NEBRASKA STAR PARTY * * July 18-23, 2004, Merritt Reservoir * * http://www.NebraskaStarParty.org * ********************************************** |
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MER-B Dimes images
Highly unlikely, since this photo is almost certainly being taken from a
quite high altitude, and your alleged "shadow" is a substantial fraction of the large crater's diameter --- whereas even the lander's parachute is quite small compared to the diameter of a typical aregraphical feature! Unlikely. If you take the series as a sequence, you'll notice the feature is absent from the first frame taken at 1986 m of height, quite near to the crater and dimmer on the second taken at 1690 m of height, and has moved again from the crater and become more distinct and larger on the third taken at 1404 m of height. Jan |
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MER-B Dimes images
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