The Martian Sky |
The Martian Sky |
Oct 11 2009, 06:41 PM
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
I have been attempting to make computer generated images of the Martian atmosphere, both as seen from the surface and from space. To check the results I have been looking for spacecraft images to use as ground truth. I have found lots of images - by far the best ones I have found are from UMSF in this thread: http://www.unmannedspaceflight.com/index.php?showtopic=3324
However, I'm always looking for more ;-). So if anyone knows of more and/or better images I'm interested in them. What would be best are mosaics showing the sky from the horizon (with the horizon/surface visible) and towards the zenith. The sky varies a lot because of variable amount of dust but the general impression I get is that the sky is bright near the horizon (usually brighter than the surface) but gets much darker higher in the sky. There is probably a fairly large, bright area in the sky near the sun, possibly less reddish (lower R/B ratio) than parts of the sky farther from the sun. I'm already getting fairly interesting results, this one has a field of view of 90 degrees: (needless to say this one is 'overexposed' near the horizon; dynamic range is sometimes a problem) The problem is that even though this may not be bad the limb currently appears far too bright as seen from space : This shows that my atmospheric model is erroneous in some way - I suspect that as seen from the surface the Martian sky is darker high above the horizon than I have been assuming. |
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Jan 24 2022, 12:02 AM
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Martian Photographer Group: Members Posts: 353 Joined: 3-March 05 Member No.: 183 |
The Sun was saturated in the recent M2020 sunset image.
The Sun is in fact slightly blue when low in the sky, but only slightly. That is mentioned here, which showed the dust to be several percent more transparent to blue light compared to slightly infrared. The blue around the Sun is almost entirely a diffraction effect, where the width of the diffraction lobe is directly proportional to wavelength--the blue is more concentrated. The particle size distribution of the dust is numerically dominated by sub-micron particles (in the math, since they are not very impactful) but area and mass are dominated by larger particles (within about 50% of 1.5 microns and larger than 1.5 microns, respectively). The sky brightness 90 degrees from the Sun is not consistent with Mie scattering, which has been known since Viking--this is not troublesome, since there is no known process to get spherical dust. It is small enough and compact enough to have Mie scattering work pretty well--especially for diffraction--but Mie still misses the details. |
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