Light on Titan

Sunshine on Titan has to be 1/100 of that we have on Earth, because
Titan is 10 time farer than us from the Sun.
So, the Huyghen after landing get on a light to get pictures.

But how Huyghens could take landscape pictures?

ÿóÿý


L' U N I O N E fa la forza

rnesto wrote:
But how Huyghens could take landscape pictures?

You said that Saturn has 1/100th the sunlight that Earth does, which is
correct. However, let me say that another way:

"At Saturn's orbit, there is about 14 watts per square meter."

Some comparisons:

If you put a single 100-watt lightbulb in a 3m x 3m room (a bedroom),
you would have 11.1 watts per square meter. At night, you would
probably think that the bedroom was brightly lit.

The light of a full moon on Earth is enough for careful landscape
photography. When your eyes adapt to full moonlight, it can even seem
bright. But it is only .001 watts per square meter.

Titan starts off with dim sunlight (14W/m^2), and then adds thick haze.
However, it is probably better lit than Earth under a full moon, so
there was enough light for landscape photos.

Huygens used lamps on the ground because it provided light of known
power and color, which was useful for certain scientific measurements.

Mike Miller

rnesto wrote:
Sunshine on Titan has to be 1/100 of that we have on Earth, because
Titan is 10 time farer than us from the Sun.
So, the Huyghen after landing get on a light to get pictures.

But how Huyghens could take landscape pictures?

Perhaps a more sensitive camera, or longer exposure times, or maybe
both.

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to raj in cup.hp.com but NOT BOTH...

JRS: In article .com
, dated Mon, 28 Feb 2005 04:40:43, seen in news:sci.space.science,
posted :
rnesto wrote:
But how Huyghens could take landscape pictures?

You said that Saturn has 1/100th the sunlight that Earth does, which is
correct.

Agreed, neglecting weather.

However, let me say that another way:

"At Saturn's orbit, there is about 14 watts per square meter."

That's not light, that's total radiative energy. A significant
proportion will be above or below visible frequencies.


Some comparisons:

If you put a single 100-watt lightbulb in a 3m x 3m room (a bedroom),
you would have 11.1 watts per square meter. At night, you would
probably think that the bedroom was brightly lit.

A 100 watt incandescent bulb does not give 100 watts of light; put your
hand on one that's been running for a while to check that. The true
figure is nearer 1 watt of light, though I don't recall exactly. But to
convince yourself that it is a lot less, consider the new fluorescent
bulbs, and how much less power they need for the same light.

Apart from that, you would only get 11.1 watts per square metre if all
of those 100 watts were to fall on the floor, or at least were
ultimately absorbed there. Or, if you prefer, the ceiling. But
everything else, including door, windows, and furnishings, would need to
be white.

The light of a full moon on Earth is enough for careful landscape
photography. When your eyes adapt to full moonlight, it can even seem
bright. But it is only .001 watts per square meter.

The figure is about right; the Moon receives about 1400 W/m^2, and
reflects IIRC somewhat under a tenth - the rest it will re-radiate, but
not in the visible. The Moon is about 0.01 r across, so 10^5 would fill
the sky above & below. But that 1400 W/m^2 is total radiative energy,
not just light.

Titan starts off with dim sunlight (14W/m^2), and then adds thick haze.
However, it is probably better lit than Earth under a full moon, so
there was enough light for landscape photos.


On Earth, there's enough light under all but the stormiest clouds; and
any cloud is substantially opaque. If "haze" is accepted as a
reasonable description, implying marginal opacity, then there should be
adequate light.

--
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" wrote:

rnesto wrote:
But how Huyghens could take landscape pictures?

You said that Saturn has 1/100th the sunlight that Earth does, which is
correct. However, let me say that another way:

"At Saturn's orbit, there is about 14 watts per square meter."

Some comparisons:

If you put a single 100-watt lightbulb in a 3m x 3m room (a bedroom),
you would have 11.1 watts per square meter. At night, you would
probably think that the bedroom was brightly lit.

The light of a full moon on Earth is enough for careful landscape
photography. When your eyes adapt to full moonlight, it can even seem
bright. But it is only .001 watts per square meter.

Titan starts off with dim sunlight (14W/m^2), and then adds thick haze.
However, it is probably better lit than Earth under a full moon, so
there was enough light for landscape photos.

Huygens used lamps on the ground because it provided light of known
power and color, which was useful for certain scientific measurements.

Mike Miller

Thank you very much!

other questions:

with 14W/m^2 and a thick atmosphere don't you think the temperature on
Titan has to be a little more higher that -180 degrees?

Do you know if Saturn were in the Titan sky during the Huygens
landing? And if yes, how much light it added to which of the Sun?
And the night on Titan with Saturn in the Sky, how many watts arrive
on the Titan surface?

Thank you for your attention. Ciao
Ernesto

On Mon, 28 Feb 2005, wrote:

Titan starts off with dim sunlight (14W/m^2), and then adds thick haze.
However, it is probably better lit than Earth under a full moon, so
there was enough light for landscape photos.

This is scarcely quantitative, but at one of the Huygens press conferences,
Martin Tomasko, principal investigator of the Descent Imager, described
compared the surface images to "taking pictures of an asphalt parking lot at
dusk."

--
"I showed *Dark Star* to a date once. | Bill Higgins
Surprisingly, she forgave me, | Fermilab
but the really amazing thing |
is that she later consented to marry me. :-)" | Internet:
-- Kent Budge, Sandia |

On Tue, 01 Mar 2005 19:03:59 GMT
(rnesto) wrote:

with 14W/m^2 and a thick atmosphere don't you think the temperature on
Titan has to be a little more higher that -180 degrees?

No, it sounds about right to me. But I bet if Titan had some heat
generating industry it would be a lot warmer. -180 degrees is better
expressed as 90 kelvin. About half the coldest temperature ever seen in
Antarctica.
--
Michael Smith
Network Applications
www.netapps.com.au | +61 (0) 416 062 898
Web Hosting | Internet Services

Dr John Stockton wrote:
That's not light, that's total radiative energy. A significant
proportion will be above or below visible frequencies.

Sure. I was just setting a high mark. Because...

The true figure is nearer 1 watt of light, though I don't
recall exactly.

...in this case, using the higher value was being conservative. If a
100W light bulb generated less visible light per square meter than my
upper bound estimate, then a 'common real world' lighting environment
is even closer to Titan.

Mike Miller

Rick Jones wrote:

rnesto wrote:
Sunshine on Titan has to be 1/100 of that we have on Earth, because
Titan is 10 time farer than us from the Sun.
So, the Huyghen after landing get on a light to get pictures.

But how Huyghens could take landscape pictures?

Perhaps a more sensitive camera, or longer exposure times, or maybe
both.

Sunshine on Tital woul be 1/100 with a sky without clouds. With the
tick clouds I think on Titan there is just 1/10000 of our terrestrial
sunshine.

Anyone could answer to these questions?

Which hour was, in the Titan day, when Huygens took its pictures?

Where was Saturn, in the Titan sky, in those hours?

Is it possible to see Saturn from the Titan surface, even when it's in
its sky?

Thank you.

ÿóÿý

(rnesto) writes:
Rick Jones wrote:

rnesto wrote:
Sunshine on Titan has to be 1/100 of that we have on Earth, because
Titan is 10 time farer than us from the Sun.
So, the Huyghen after landing get on a light to get pictures.

But how Huyghens could take landscape pictures?

Perhaps a more sensitive camera, or longer exposure times, or maybe
both.

Sunshine on Tital woul be 1/100 with a sky without clouds. With the
tick clouds I think on Titan there is just 1/10000 of our terrestrial
sunshine.

That assumes the clouds block 99% of incoming sunlight. I have no
idea what the actual figure is, but my wild guess is that more gets
through than that.

Even assuming 99% blockage, it would still be about 40 times as bright
as full moonlight on Earth. That should be more than enough to take
pictures. (One reference says it was like photographing asphalt at
dusk.)

Anyone could answer to these questions?

Which hour was, in the Titan day, when Huygens took its pictures?

Where was Saturn, in the Titan sky, in those hours?

I have no idea -- but since Titan's rotation is synchronous, the
position of Saturn in its sky doesn't depend significantly on the time
of day. (A "day" on Titan is just under 16 Earth days.)

Is it possible to see Saturn from the Titan surface, even when it's in
its sky?

The view of Saturn from Titan's surface (in visible light) should be
about as good as the view of Titan's surface from above its atmosphere
-- i.e., essentially none.

--
Keith Thompson (The_Other_Keith) http://www.ghoti.net/~kst
San Diego Supercomputer Center * http://users.sdsc.edu/~kst
We must do something. This is something. Therefore, we must do this.