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The quality of light on Titan
I'm a little surprised at the good visibility on Titan.
I mean, from those shots a few miles up, under the clouds and approaching the surface, and then, from the surface photos, we seem to be able to see a long way. Considering we're under cloud cover, and all the way out at Saturn. Do the cameras have some sort of light amplication cranked up, or is this pretty much what the naked eye would see on Titan? |
#2
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On Tue, 25 Jan 2005 01:05:24 GMT, "Algomeysa2"
wrote: I'm a little surprised at the good visibility on Titan. I mean, from those shots a few miles up, under the clouds and approaching the surface, and then, from the surface photos, we seem to be able to see a long way. Considering we're under cloud cover, and all the way out at Saturn. Do the cameras have some sort of light amplication cranked up, or is this pretty much what the naked eye would see on Titan? No amplification required, because it isn't that dim. The light at Saturn is 1% of what it is at Earth, which means (in human terms) comfortably bright. And it seems that the clouds are at high altitude- that is, they don't extend to the ground. The lower atmosphere itself seems rather clear. The light at the surface is probably something like what you would have here on a very stormy day, and the images as they are returned are similar to what you would see if you were there. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#3
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I think somewhere on either the Cassini or Huygens web site, they state that the
measurements from one of the Huygens instruments shows that, at the surface, the lighting is about what you see at either mid dusk or dawn, more than enough to see around but you don't need sunglasses. ^_^ -- Sincerely, --- Dave ---------------------------------------------------------------------- It don't mean a thing unless it has that certain "je ne sais quoi" Duke Ellington ---------------------------------------------------------------------- "Chris L Peterson" wrote in message news On Tue, 25 Jan 2005 01:05:24 GMT, "Algomeysa2" wrote: I'm a little surprised at the good visibility on Titan. I mean, from those shots a few miles up, under the clouds and approaching the surface, and then, from the surface photos, we seem to be able to see a long way. Considering we're under cloud cover, and all the way out at Saturn. Do the cameras have some sort of light amplication cranked up, or is this pretty much what the naked eye would see on Titan? No amplification required, because it isn't that dim. The light at Saturn is 1% of what it is at Earth, which means (in human terms) comfortably bright. And it seems that the clouds are at high altitude- that is, they don't extend to the ground. The lower atmosphere itself seems rather clear. The light at the surface is probably something like what you would have here on a very stormy day, and the images as they are returned are similar to what you would see if you were there. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#4
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On the cloud tops of Titan there's 72 times darker than on earth clowd
tops. Earth's atmosphere passes through 63% of sunlight on a shiny day. Titan's atmosphere is 10 times heavier and passes 10% of sunlight. After a rough estimation, Titan's surface receives from 1/1000 to 1/500 of light which comes to Earth's surface. It's in fact much darker than on a very stormy day, it's more like late dusk, or at night, something like 20-30 meters away from a streetlight. You'll really need some sort of artificial lighting there to feel comfortable, and some serious cloth Huygens cameras were specially designed to take piclures in such dark conditions, so don't take those photos literally -- they don't depict the real ilumination... Some 3rd-party pics are he http://anthony.liekens.net/huygens_static.html |
#5
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On 27 Jan 2005 05:50:38 -0800, "Intertracer"
wrote: On the cloud tops of Titan there's 72 times darker than on earth clowd tops. Earth's atmosphere passes through 63% of sunlight on a shiny day. Titan's atmosphere is 10 times heavier and passes 10% of sunlight. After a rough estimation, Titan's surface receives from 1/1000 to 1/500 of light which comes to Earth's surface. It's in fact much darker than on a very stormy day, it's more like late dusk, or at night, something like 20-30 meters away from a streetlight. You'll really need some sort of artificial lighting there to feel comfortable, and some serious cloth By my calculation, Saturn (now 9.1 AU from the Sun) receives 1.2% of the sunlight received at the Earth. The amount of sunlight absorbed is more difficult to calculate than simply comparing atmospheric density. The Earth's atmosphere actually only attenuates about 20% of the incident light, and much of that is scattered, not absorbed. Assuming your value of 10% transmission for Titan, however, the surface light will be 0.12% of Earth's. On the Earth, at local noon over the middle and tropical latitudes, the illumination is about 130,000 lux. So at local noon on Titan, figure 160 lux. That's quite a bit brighter than a darkly overcast day on the Earth, which measures at 100 lux, and some 600 times brighter than the full Moon. Office lighting guidelines normally specify 100 to 400 lux as the target range. Late twilight is normally taken as 10 lux. In other words, the illumination on Titan would be quite comfortable for human eyes- no artificial illumination required for most tasks. Huygens cameras were specially designed to take piclures in such dark conditions, so don't take those photos literally -- they don't depict the real ilumination... Huygens was provided with a light source to use in the event conditions were very dark. I'm not sure if it was used or not. The camera is quite ordinary in its sensitivity- just a typical CCD. There is no special light amplification used. I believe what we are seeing in these images is pretty much what we would see with our own eyes. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#6
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In fact, clowds appeared to be densier and lower than expected. The
bottom margin is 30km (50-70km was predicted). 600 times darker look reasonable. As for the DISR cameras -- in fact they took only a few meaningful pictures with the light source in act. As far as I know these cams don't have a big aperture (maybe just a few millimeters), it's interesting though what exposure was used. DISR at a glance: http://www.lpl.arizona.edu/~kholso/overview.htm |
#7
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Chris L Peterson wrote:
So at local noon on Titan, figure 160 lux. T This is in (exactly ?)the same "ballpark" as Nasa's own quoted figures. Steve |
#8
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On Thu, 27 Jan 2005 16:37:33 +0000, Steve
wrote: This is in (exactly ?)the same "ballpark" as Nasa's own quoted figures. Now you tell me! g. So I wasted my time with all those back-of-the-envelope calculations. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#9
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"Intertracer" wrote:
In fact, clowds appeared to be densier and lower than expected. The bottom margin is 30km (50-70km was predicted). 600 times darker look reasonable. As for the DISR cameras I read that as DSLR at first. I had images of a Digital Rebel hanging off the bottom of Huygens Tim -- This is not my signature. |
#10
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Chris L Peterson wrote:
By my calculation, Saturn (now 9.1 AU from the Sun) receives 1.2% of the sunlight received at the Earth. The amount of sunlight absorbed is more difficult to calculate than simply comparing atmospheric density. The Earth's atmosphere actually only attenuates about 20% of the incident light, and much of that is scattered, not absorbed. Assuming your value of 10% transmission for Titan, however, the surface light will be 0.12% of Earth's. On the Earth, at local noon over the middle and tropical latitudes, the illumination is about 130,000 lux. So at local noon on Titan, figure 160 lux. That's quite a bit brighter than a darkly overcast day on the Earth, which measures at 100 lux, and some 600 times brighter than the full Moon. Office lighting guidelines normally specify 100 to 400 lux as the target range. Late twilight is normally taken as 10 lux. In other words, the illumination on Titan would be quite comfortable for human eyes- no artificial illumination required for most tasks. During daytime. The Titan night length is equal to 8 Earth days. |
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