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The quality of light on Titan



 
 
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  #1  
Old January 25th 05, 02:05 AM
Algomeysa2
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Default 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  
Old January 25th 05, 02:15 AM
Chris L Peterson
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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  
Old January 25th 05, 02:43 AM
David Nakamoto
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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  
Old January 27th 05, 02:50 PM
Intertracer
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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  
Old January 27th 05, 04:54 PM
Chris L Peterson
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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  
Old January 27th 05, 05:31 PM
Intertracer
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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  
Old January 27th 05, 05:37 PM
Steve
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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  
Old January 27th 05, 07:09 PM
Chris L Peterson
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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  
Old January 27th 05, 08:15 PM
Tim Auton
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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  
Old January 28th 05, 02:42 AM
Scott M. Kozel
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Default

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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