Dust Storm- Opportunity EOM, the end of the beginning of a new era in robotic spaceflight |
Dust Storm- Opportunity EOM, the end of the beginning of a new era in robotic spaceflight |
Jun 5 2018, 03:05 PM
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
Expect a quiet few sols - http://www.lpl.arizona.edu/~lemmon/mars-tau-b.html
SOL TAU 5097 0.65 5098 0.64 5099 0.67 5100 0.64 5101 0.60 5102 0.60 5103 0.61 5104 1.55 5105 **** 5106 2.12 |
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Jun 15 2018, 01:46 PM
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Martian Photographer Group: Members Posts: 353 Joined: 3-March 05 Member No.: 183 |
Exactly! The Sun itself was fainter than a full moon on Earth on Sunday. But in each photon-dust interaction the extinction (which tau measures) is <10% absorption and >90% scattering to sky light. The scattering is ~85% downward, 15% upward. There would be 10-11 extinction events (more like 14-15 at the time Opportunity was awake, with the Sun not vertical). Modeling literally the round numbers I just used, I get 98% loss of light at the surface (i.e., sky light >10,000 times direct sun light); you got 97% (and I believe the panels more than made up numbers).
What did it look like? Other than the decidedly ruddy to brownish tint, it looked like a somewhat overcast day. The sort of mid-afternoon when you can just barely see (or not quite see) the Sun through clouds that stretch from horizon to horizon. When the world would be black through eclipse glasses, but easily visible without. Normal human vision would adapt well--it's not night, moonless or moonlit, or even sunset. Solar panels, however, are not known for being so dark-adaptable. So the drama is real, even if people seem to want to describe it in terms that would be as dramatic for people as the actual situation is dramatic for the rover. This weekend, I expect tau of several hundred. Not on Mars, but at home, where we expect thunderstorms. PS, scattered light is not 'neglected'. In photometrically measuring opacity it is hunted and eliminated with extreme prejudice. |
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Jun 15 2018, 04:37 PM
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#3
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
The sort of mid-afternoon when you can just barely see (or not quite see) the Sun through clouds that stretch from horizon to horizon. Another example that people may have witnessed is being under heavy smoke from forest fires. The sun may be just barely visible as a dull orange disk (so a huge tau), but the landscape will be as bright as some level of cloudy day due to light scattered from the sky (smoke). I don't know how smoke particle size compares with Martian dust, which would affect the details of the scattering (how much into what angles vs frequency), so the details may be different. Still it's worth pointing out that so far 22 Whrs/sol is an upper limit... |
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