[X] My Assistant

[Nirgal]

among the many new pancams at exploratorium there seem to be interesting
images showing what must be clouds, clearly defined as never seen before
at the Gusev site.

http://qt.exploratorium.edu/mars/spirit/pa...HEP2680L7M1.JPG

Interestingly, those are high-res pancam multi-filter sequences.

Questin for Dan (slinted) refering to our recent discussion about sky color:
would't this be wotrth a try to do interesting sky color composites.
Maybe you could use the brightest pixels
in the clouds as a white point reference ?

[edstrick]

Oh... regarding the discussion of ice clouds as "white balance" targets...

Viking repeatedly imaged a pattern of extremely high <some 25 kilometer> clouds which were textured with a lot of fine detail in one region southwest of Tharsis. Something like 30 degrees south, 160 or 170 degrees east. (I'm very unsure of the coordinates without checking)

Water ice clouds on Mars tend to be very diffuse, though some imaged from the rovers do have a fair bit of fine detail, but nothing like these. At the low temps <especially at altitude> where ice hazes are present, ice -- even micron-sized -- takes a long time to condense or sublimate, making the clouds diffuse. The combined analysis of limited atmosphere thermal sensing from the Viking Infrared Thermal Mapper, and radio occultation atmosphere profiles, together with the characteristics of the clouds, were that these were CO2 ice clouds, formed by "orographic" waves in the middle atmosphere causing temperatures to persistantly drop below CO2 ice formation temperatures for that altitude.

Someday we'll see them from the surface.

[Nirgal]

I too have always been fascinated by the question how the martin sky would really look like beacuse none of the spacecraft so far has provided a
real wide-angle view of the sky *including* ground/horizon parts.
Although the MER's have already collected very extensive sky studies with the
pancam, most of it were isolated strips or the parts around the sun.
So, because of the contrast streching, that does not tell us much how the big picture would look like in composition with the ground.

For a long time I was a strong advocate of the "nearly-black-sky-not-far-away-from-horizon"- fraction (it's just hard to imagine else when considering an atmosphere
more than one hundred times thinner than earth's)

In the mean time I have collected quite a few rover images, that do show
a considerable angle of sky away from the horizon, and it's interesting
how much this seems to support the "black-sky"-thesis, e.g.:

http://marsrovers.jpl.nasa.gov/gallery/pre..._Opp-B163R1.jpg
http://marsrovers.jpl.nasa.gov/gallery/all...46P0833R0M1.JPG

remarks:
1. as already pointed out, the "absolute blackness-level" is probably exagerated
by the contrast stretching (would be easy to resolve by looking at the raw/
radiance calibrated images)
However, Contrast stretching tends to darken *all* black/dark parts of the image,
i.e. the shadoes of the rocks: so in the images above, the sky appears at least as dark than the shadows of the rocks.

2. Vignetting effects of the camera lens towards the edges of the field of view
can also contribute to the "black-sky" effect. However in the images above it is
obvious that the "blackening" already starts in the middle of the field of view

So in summary, I tend to imagine the sky as bright near horizon, but
getting near black very soon, with a sharp gradient.

However this is probably only so during relatively dust-free periods (low atmospheric tau). In more dusty conditions, the gradient will probably
become much less sharp ...

Qeustion: Are there also navcam-sky-images like the ones above taken during
more dusty (high tau) periods ?

[Marcel]

I'd like to know what the nightsky looks like at Mars. Would the atmosphere be more transparent (better seeing ?) than earths ? Would earth look as bright as Venus from here ? Would it be as blue, as Mars is red from here ?

[odave]

I'd like to know what the nightsky looks like at Mars. Would the atmosphere be more transparent (better seeing ?) than earths ? Would earth look as bright as Venus from here ? Would it be as blue, as Mars is red from here ?

I've been fascinated by the amateur astronomy done so far by the MERs - I say "amateur" because they are geologists (aerologists?) by trade

I would think the seeing may be worse with all the dust blowing around, but then the atmosphere is a lot thinner. I wonder, too, what kind of details one could observe on the Earth from Mars? Would my 8" f/10 SCT at 200x show clouds and ocean? Any hints of land masses? We can certainly see surface features on Mars, so I'd assume the view of Earth would be at least as detailed. How about night-side light pollution from cities at that distance? I'd think not - probably too small and too dim as compared to the reflected sunlight. (You can see light pollution from orbit, how about from the Moon?)

It would be quite an observing session - and you don't need to put up with that pesky dew!