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Explorer1

Jan 30 2018, 01:17 AM

QUOTE (scalbers @ Jan 29 2018, 07:50 PM)

The best part of the sky to look would be somewhat lower than the zenith and opposite the sun in azimuth.

And the best place to look from is probably the summit of Olympus Mons! One of the only spots, along with the other volcanoes, where not even the global dust storms can reach. 12% the atmospheric pressure, right? Not even Mauna Kea gets close to that in terms of ideal observing locations...

antipode

Jan 30 2018, 05:34 AM

Hi all, OP here (at least in terms of Mars' sky at the zenith question).

Yes, I did mean during the daytime. This question was prompted by 2 things.

1. All the pre Viking paintings of Mars' surface that showed a thin blue band around the horizon.
This came before we knew the amount of fines suspended in the atmosphere, but I always assumed that at 7mb, the sky directly above the viewer would be dark enough
(assuming the Sun wasn't close in the sky) to see stars. Or would it be like the Moon, where glare and contrast extremes apparently made it near impossible for the astronauts to see stars?

2. Now add the fines we know are always there to some extent. Take a nice relatively dust free day at Gale (for instance) and look straight up. With the caveat about the Sun still standing,
would you see butterscotch all the way to the zenith, with just the color slowly darkening - or would the sky be effectively black? And if it was black, what would be the chance of seeing say, a magnitude 1 star?

P

ngunn

Jan 30 2018, 09:57 AM

I seem to recall one of the rovers acquired at least one vertical sky panorama. Maybe someone can link back to that and any related discussion from that time.

scalbers

Jan 30 2018, 02:36 PM

QUOTE (antipode @ Jan 30 2018, 05:34 AM)

with just the color slowly darkening - or would the sky be effectively black? And if it was black, what would be the chance of seeing say, a magnitude 1 star?

As a first approximation the sky brightness relative to the sun's brightness at the zenith is proportional to the aerosol optical depth (AOD) times the phase function that applies for the scattering angle at that part of the sky. Other parts of the sky are brighter based on the cosine of the zenith angle. Thus the sky brightness could be a little darker than Earth in some spots, though not really black. The depth of the phase function minimum (near 140 degrees scattering angle) would be important. The AOD (+gas) is about a factor of 2 disadvantage typically on Mars vs Earth and the phase function gives an advantage of about 6 times in the darkest portion of the sky.

With the sun 51 degrees high the non-MC method (I sometimes call this method Simulated Weather Imagery or SWIM, as shown in the post #42 upper image), gives a zenith limiting magnitude of about -3.2. This phase function is roughly 10 times smaller as we get farther from the sun, though reflection from the ground smooths out the variation. So far I obtain that the theoretical best place to look is 55 deg high opposite the sun's azimuth with a limiting magnitude of -2.6. Jupiter in this situation may be invisible as it would be a fainter magnitude when at that elongation from the sun. A lower sun would of course improve things. Nudging Jupiter underneath the best limiting magnitude spot would increase its (top of atmosphere) brightness as well, since it would then have a larger elongation.

mcaplinger

Jan 30 2018, 03:55 PM

QUOTE (ngunn @ Jan 30 2018, 01:57 AM)

I seem to recall one of the rovers acquired at least one vertical sky panorama.

See MSL sol 1637 (I think) and sol 1817.

I'm pretty sure it's never dark enough at the zenith to see stars from elevations anywhere near the datum. Top of Olympus Mons, I don't know.

Without doing the math in detail, I think the following is true: if you could see Jupiter in the daytime, it would be like seeing Venus in the daytime on Earth -- possible if you know just where to look, but not anything like obvious.

scalbers

Jan 30 2018, 04:45 PM

Olympus Mons should be pretty good as I'm getting limiting magnitudes of about zero, using the earlier mentioned 12% of the atmosphere and recalling the similar scale heights for gas and dust.

JRehling

Jan 30 2018, 07:29 PM

I'm not sure how much the martian sky varies, but the terrestrial sky, needless to say, varies enormously, even when cloudless. I've heard of lifelong earthlings who are unaware that the Moon is visible in the daytime sky, and indeed, it's a lot less visible in low-transparency, high-humidity conditions (and climates) than otherwise.

In what must have been profoundly unusual circumstances, I saw satellites orbiting overhead in Phoenix during the daytime. Not a flare, which can exceed Venus in brightness, but during typical illumination.

Those who have tried report that it's easier to see redder stars through a telescope in the daytime sky than whiter ones. The reason is obvious: greater contrast against the blue sky. So I would imagine that Sirius would be the easiest to see on Mars, whereas Arcturus is possibly easiest on Earth.

Of course, the elephants in the room for Mars are Phobos and Deimos. How visible are they in a daytime sky?

And Venus and Earth ought to be interesting daytime objects to consider. Blue Earth ought to contrast nicely with the orange sky.

mcaplinger

Jan 30 2018, 08:22 PM

QUOTE (JRehling @ Jan 30 2018, 11:29 AM)

Of course, the elephants in the room for Mars are Phobos and Deimos. How visible are they in a daytime sky?

https://mars.nasa.gov/msl/multimedia/raw/?r...1_DXXX&s=45 was taken at 17:27 LMST, which I think was somewhat before sunset.

Ant103

Jan 30 2018, 11:33 PM

Actually, there was a Mastcam mosaic of the sky, near and on the zenith conducted by Curiosity on Sol 101. It was quite a challenge to stitch it because of the lack of control points usable, but I used imagery metadatas to place them exactly in their good position.
Anyway, this shows us that the zenith is not black, but more brownish. But, it could be very dark because I don't have the information about the exposure length of this set of images.

fredk

Jan 31 2018, 12:20 AM

QUOTE (mcaplinger @ Jan 30 2018, 09:22 PM)

https://mars.nasa.gov/msl/multimedia/raw/?r...1_DXXX&s=45 was taken at 17:27 LMST, which I think was somewhat before sunset.

Given its field of view, the M-100 image might correspond more closely to a binocular view than a naked eye view, so Phobos will be harder naked eye. But I think very likely still visible during the day.

For viewing through an optical system, aperture helps with point sources against a bright sky even more than extended sources, since the brightness of the point source will be enhanced by about the ratio of aperture to pupil area, while the surface brightness of the sky will never exceed that seen by naked eye. On Earth brighter stars are easily visible through telescopes in daylight, most notably around lunar transits.

JRehling

Jan 31 2018, 04:27 PM

Great shot of Phobos, mcaplinger! (I assume that's not Deimos, simply because Phobos would be the easier shot.) Phobos should be visible every day, then.

scalbers

Jan 31 2018, 07:39 PM

QUOTE (Ant103 @ Jan 30 2018, 11:33 PM)

Actually, there was a Mastcam mosaic of the sky, near and on the zenith conducted by Curiosity on Sol 101.

Interesting to see this Damia - thanks for posting. Would you happen to recall the geometry or map projection of your mosaic?

vikingmars

Jan 31 2018, 08:29 PM

QUOTE (Ant103 @ Jan 31 2018, 12:33 AM)

Congratulations Ant 103 for this superb work of yours.
As a reminder, here are the sky pics from VL1...
Please, note that the color saturation of the sky changes with the dust opacity and with the Martian seasons.
Enjoy

Click to view attachment

mcaplinger

Jan 31 2018, 09:11 PM

QUOTE (Ant103 @ Jan 30 2018, 03:33 PM)

Actually, there was a Mastcam mosaic of the sky, near and on the zenith conducted by Curiosity on Sol 101.

Looks like there was one survey done on sol 100 at around noon, and then another on sol 101 in the late afternoon. All of these images were autoexposed but the exposure times can be pulled out of the PDS index file https://pds-imaging.jpl.nasa.gov/data/msl/M...EX/EDRINDEX.TAB . (Second column below.) Of course, to be really quantitative one would have to linearize the square-root images.

CODE

"0100ML0004900050102961E01_XXXX.LBL"      1.0 "0  " "Sol-00100M11:58:10.077      "
"0100ML0004930000102962E01_XXXX.LBL"      4.0 "0  " "Sol-00100M11:59:11.392      "
"0100ML0004930010102963E01_XXXX.LBL"      5.0 "0  " "Sol-00100M11:59:25.017      "
"0100ML0004930020102964E01_XXXX.LBL"      5.0 "0  " "Sol-00100M11:59:38.643      "
"0100ML0004930030102965E01_XXXX.LBL"      2.5 "0  " "Sol-00100M12:00:10.760      "
"0100ML0004930040102966E01_XXXX.LBL"      2.8 "0  " "Sol-00100M12:01:16.941      "
"0100ML0004930050102967E01_XXXX.LBL"      5.5 "0  " "Sol-00100M12:01:35.433      "
"0100ML0004930060102968E01_XXXX.LBL"      6.9 "0  " "Sol-00100M12:01:51.978      "
"0100ML0004930070102969E01_XXXX.LBL"      6.9 "0  " "Sol-00100M12:02:05.604      "
"0100ML0004930080102970E01_XXXX.LBL"      5.6 "0  " "Sol-00100M12:02:21.176      "
"0100ML0004930090102971E01_XXXX.LBL"      7.4 "0  " "Sol-00100M12:02:38.695      "
"0101ML0006740000102999E01_XXXX.LBL"      6.4 "0  " "Sol-00101M15:40:03.764      "
"0101ML0006740010103000E01_XXXX.LBL"      3.5 "0  " "Sol-00101M15:40:55.347      "
"0101ML0006740020103001E01_XXXX.LBL"      5.7 "0  " "Sol-00101M15:41:15.785      "
"0101ML0006740030103002E01_XXXX.LBL"      7.6 "0  " "Sol-00101M15:41:31.357      "
"0101ML0006740040103003E01_XXXX.LBL"      9.0 "0  " "Sol-00101M15:41:47.902      "
"0101ML0006740050103004E01_XXXX.LBL"     10.1 "0  " "Sol-00101M15:42:04.447      "
"0101ML0006740060103005E01_XXXX.LBL"     10.1 "0  " "Sol-00101M15:42:19.046      "
"0101ML0006740070103006E01_XXXX.LBL"     10.1 "0  " "Sol-00101M15:42:34.618      "
"0101ML0006740080103007E01_XXXX.LBL"     11.3 "0  " "Sol-00101M15:42:50.190      "
"0101ML0006740090103008E01_XXXX.LBL"     13.6 "0  " "Sol-00101M15:43:05.762      "
"0101ML0006740100103009E01_XXXX.LBL"     15.9 "0  " "Sol-00101M15:43:21.335      "
"0101ML0006740110103010E01_XXXX.LBL"     17.7 "0  " "Sol-00101M15:43:36.907      "
"0101ML0006740120103011E01_XXXX.LBL"     17.7 "0  " "Sol-00101M15:43:51.505      "
"0101ML0006740130103012E01_XXXX.LBL"     13.9 "0  " "Sol-00101M15:44:15.837      "
"0101ML0006740140103013E01_XXXX.LBL"     13.9 "0  " "Sol-00101M15:44:29.462      "
"0101ML0006740150103014E01_XXXX.LBL"     13.9 "0  " "Sol-00101M15:44:43.088      "
"0101ML0006740160103015E01_XXXX.LBL"     11.1 "0  " "Sol-00101M15:44:58.660      "
"0101ML0006740170103016E01_XXXX.LBL"     19.7 "0  " "Sol-00101M15:45:19.098      "
"0101ML0006740180103017E01_XXXX.LBL"     13.6 "0  " "Sol-00101M15:45:48.296      "
"0101ML0006740190103018E01_XXXX.LBL"     16.2 "0  " "Sol-00101M15:46:13.600      "
"0101ML0006740200103019E01_XXXX.LBL"     16.2 "0  " "Sol-00101M15:46:27.226      "
"0101ML0006740210103020E01_XXXX.LBL"     16.2 "0  " "Sol-00101M15:46:43.771      "
"0101ML0006740220103021E01_XXXX.LBL"     14.0 "0  " "Sol-00101M15:46:59.343      "
"0101MR0004910040104491E01_XXXX.LBL"      0.5 "0  " "Sol-00101M15:49:01.000      "
"0101ML0004910050103023E01_XXXX.LBL"      1.0 "0  " "Sol-00101M15:49:33.117      "

Deimos

Jan 31 2018, 11:35 PM

Navcam images of Phobos just before & after sunset: https://photojournal.jpl.nasa.gov/catalog/PIA17270. Look in PDS for the lossless version of the image mcaplinger posted; and see http://www.planetary.org/blogs/emily-lakda...phobos-msl.html.

Overall, daytime visibility of Phobos is very seasonal. Omitting non-rover sites, and the advantages trained observers have, especially with positional cues, it is unlikely any other stars would be easily visible in most conditions. The Mastcam mosaics (sol 100, 101) were taken in a moderate dust storm. Even so, the sky never clears, and there are many images of zenith that show this (see Navcam zenith movies and many Mastcam images on PDS, where exposure times can be found). But, Phobos is bright. In less dusty skies, it seems not too hard to see it, at least with the Sun low. With very dusty skies, no way.

There is also an approximate true color 'sky' release at http://www.planetary.org/blogs/emily-lakda...n-analemma.html. The sky part of the image was taken with the Sun nearly at zenith, and it was dusty, but it's another view (the sol 100 Mastcam survey also had a high Sun).

Note that the brightness peak near the Sun is typically supplemented by another near the horizon (high scattering path length), leaving a darkest region either partway down (if the Sun is high) or medium-low and opposite Sun if the Sun is medium-low and moving up toward zenith as the Sun sinks.

scalbers

Feb 1 2018, 12:33 AM

Indeed it's kind of similar to this earlier simulated movie with a rising sun. I'm getting a bit more confidence in the Monte Carlo code so I hope to make a movie of that version before too long.

Pretty neat Opportunity panorama too, giving a good idea of the relative brightness of the sky and land. This will help check things like the land reflection of the random light rays as the horizon sky brightness may presently be underdone (e.g. with the high sun images).

scalbers

Feb 4 2018, 12:54 AM

Here is an attempt to generate a similar polar (fisheye) projection of the Opportunity sky link two posts up. The sun is at the zenith and a generic land surface shows up in the corners.

Click to view attachment

This is simulated with the ray-tracing (non MC) code. It's a good case to test improvements in the handling of multiple scattering, so the minimum brightness now shows better midway up in the sky. To get the color reasonably close, the aerosol optical properties were adjusted quite a bit. As often happens I'm bumping up against the question of whether the color/contrast has any enhancement in the actual mosaic.

One way to help make color more objective is to specify the xy chromaticity of various points in the sky. This is done for various missions here where I was led by the Opportunity image release. Typical sky values far from the sun are x=.40, y=.38. In the simulation the xy values so far look reasonable near the horizon. As we get closer to the sun the colors are less saturated, though it doesn't tilt to all the way to bluish next to the sun as one might anticipate. With some phase function and single scattering albedo adjustments we have a second version below:

Click to view attachment

Near the horizon this has a chromaticity of x=.39, y=.38 making it a bit less orange compared to the typical values in the paper, yet a bit more tan compared with the Opportunity mosaic. A related factor is where the white point is set (for conversion to RGB) and I'm using 5800K that I also set my monitor to. This version does get slightly bluish right next to the sun. It is white here due to saturation though the blue tint would be visible in a 16-bit image. This is a good exercise for checking various aspects of color processing.

Click to view attachment

Based on this a new set of animated and individual 8/16 bit frames at various solar elevation angles (in 2 degree steps) is taking shape. Ten degrees of land surface shows up at the bottom, with some variations in brightness depicted. The frame-to-frame brightness is a bit inconsistent, though the full brightness range is accessible via the 16-bit images. An overall Mars sky website is here.

Sean

Mar 31 2018, 12:19 AM

This is wonderful work Steve.... can you please check the 16bit images? They are all appearing dark, the 8bit images are fine.

I've opened the 16bit images in Photoshop & Irfanview with the same result, very dark with a pixelated sun. Maybe I'm opening wrong?

Click to view attachment

scalbers

Mar 31 2018, 12:27 AM

Hi Sean - thanks. Good question - the intent (as before) with the 16-bit images is to have the image reside in the middle of the logarithmic brightness space so there's extra room on both the dark and bright ends. Thus to convert it to an equivalent 8-bit image one could try dividing the image by 16 and truncating at 255. How does this look? Depending on the viewer multiplying by 16 can look OK, though you'd be clipping next to the sun a bit. The actual numerical data in the images look basically OK. Interestingly the sun doesn't seem go to the max at 65535 counts. Sky areas that are 128 counts in the 8-bit images should be 2048 counts in the 16-bit ones.

Looking with a 16-bit image viewer with some type of sliding brightness scale seems like an ideal way to view the entire dynamic range. I wonder if browsers might someday support something like this. On a Mac "Photos" works to do a quick image stretch, though perhaps there's another viewer out there with better brightness controls. I looked at the numerical values by using ImageMagick to make a .ppm image with "convert -compress none". I could then see the image with a plain text editor.

JohnVV

Apr 2 2018, 04:24 AM

normally i use the gui for the vips image lib " Nip2"

it has a very handy slider for moving the gray point

screenshot

scalbers

Sep 4 2021, 06:31 PM

Thanks JohnVV. Revisiting this a bit I made a sequence of frames with a Monte Carlo ray-tracing algorithm located here:

https://stevealbers.net/ast/mars/mc/

An HTML5 viewer to see an example 16-bit frame with various brightness settings can be found here:

http://stevealbers.net/ast/mars/mc/briloop...ghtness_36.html

Click to view attachment

It still needs some work on the blue sunrise. In fact the blue color surrounding the sun should actually be present all day long in addition to sunrise/set. Exactly how strong the blue color saturation is appears open to some interpretation. Figure 10 of this paper gives a modestly blue chromaticity near sunset. Another more recent paper has some interesting discussion. It's a bit unclear how to translate this into the optical properties I'm looking for, so it's a bit of trial and error to simulate close to observed chromaticities.

scalbers

Dec 5 2021, 09:19 PM

Relating to the last linked paper above, I was able to set up some aerosol optical properties based on personal communication with the authors. The latest Monte Carlo update can be found on my website here:

http://stevealbers.net/albers/allsky/mars.html

I would note this is based on modeling the dusty atmosphere to have just coarse mode aerosols around 1.7 microns in effective radius. This gives a strong brightness difference near the sun vs farther away. It's possible (though a bit debatable) there are some finer aerosols present as well and this would reduce that contrast somewhat.

One thing to consider when combining these sky simulations with rover mosaics of the surface is that a better match can be had by considering the "BRDF" of the land surface. In other words one should account for the actual land reflectance to be brighter opposite the sun (fully lit objects plus opposition effect) and darker toward the sun (e.g. with shadows present). If a mosaic has been equalized to show uniform brightness vs azimuth it will be more challenging to match up to the simulated sky.

scalbers

Dec 27 2021, 06:21 PM

After looking at some additional papers and doing a few more experiments, I made a further Monte Carlo revision (on Jan 1 - Happy New Year) as can be seen here:

https://stevealbers.net/albers/allsky/mars.html#mc

Click to view attachment

The overall Monte Carlo algorithm has been improved in accuracy and with noise reduction. Some of the dust optical properties are described on the website, and may continue to be refined further.

scalbers

Jan 23 2022, 09:09 PM

Thanks to Damia's post in a different thread (an excellent sunset panorama) I was thinking about getting the sky simulations to better show an additional amount of blue sky near the sun when close to sunset/sunrise. A clue is that the sun's disk also then turns somewhat blue. This points to a specific optical property of the dust, variation of extinction with wavelength. I made such a modification and below is a new animation of the sky. Hopefully the overall set of optical properties is starting to converge better on reality. One question I still have is whether smaller aerosols <1 um in diameter are more present to make the sky brightness a bit more uniform as a function of azimuth.

Click to view attachment

https://stevealbers.net/ast/mars/mc/mars_cyl.mp4

fredk

Jan 23 2022, 10:37 PM

QUOTE (scalbers @ Jan 23 2022, 10:09 PM)

A clue is that the sun's disk also then turns somewhat blue.

Can we trust the colour of the disk in un-ND-filtered frames? Maybe one or more channels are saturated, even near sunrise/set?

scalbers

Jan 23 2022, 11:29 PM

QUOTE (fredk @ Jan 23 2022, 10:37 PM)

Can we trust the colour of the disk in un-ND-filtered frames? Maybe one or more channels are saturated, even near sunrise/set?

There is some consensus from other sources as well - and I'd be interested in a more precise comparison of the sun's disk chromaticity. It turns out that with the Monte Carlo simulation one seems to need a blue solar disk to get a sufficiently bluish color in the scattered light around the sun when it is low. Here is one paper about that as well. Looking at chromaticity values, perhaps there it too much blue in my example, so I'll next try an intermediate solution.

https://www.osapublishing.org/ao/fulltext.c...8&id=281919

In this paper they are at least looking very close to the sun with chromaticity when it is low.

https://trs.jpl.nasa.gov/bitstream/handle/2....pdf?sequence=1

Deimos

Jan 24 2022, 12:02 AM

The Sun was saturated in the recent M2020 sunset image.

The Sun is in fact slightly blue when low in the sky, but only slightly. That is mentioned here, which showed the dust to be several percent more transparent to blue light compared to slightly infrared.

The blue around the Sun is almost entirely a diffraction effect, where the width of the diffraction lobe is directly proportional to wavelength--the blue is more concentrated. The particle size distribution of the dust is numerically dominated by sub-micron particles (in the math, since they are not very impactful) but area and mass are dominated by larger particles (within about 50% of 1.5 microns and larger than 1.5 microns, respectively).

The sky brightness 90 degrees from the Sun is not consistent with Mie scattering, which has been known since Viking--this is not troublesome, since there is no known process to get spherical dust. It is small enough and compact enough to have Mie scattering work pretty well--especially for diffraction--but Mie still misses the details.

Deimos

Jan 24 2022, 12:19 AM

Holy Moly! That Applied Optics paper modeled the press release image?!?! I could have pointed them to the data. In the data, the Sun was saturated and not viewed through the same atmospheric path in each image since it was 3 sequential filters (for example). In the press release image, the Sun was the color I told it to be, which was taken straight from the Tomasko et al. model. I guess I'm glad someone noticed it was blue...

scalbers

Jan 24 2022, 12:31 AM

Yes we could still provide the authors with that data as I've recently been in touch with one of them

Thanks much for the links. I agree the diffraction effect is the principal reason the solar aureole is blue, especially when the sun is high and things are simpler with more single scattering. I suspect it may be more nuanced when the sun is close to the horizon since when I have near zero Angstrom Exponent much of the aureole stays somewhat redder near sunset.

My post above #74 had a very large negative Angstrom Exponent of around -1.8 between 615nm and 450nm so I'll try tests of -0.25 and -0.15 to check the sensitivity of the images.

scalbers

Feb 6 2022, 07:44 PM

Here's a animated version with -0.15 Angstrom exponent:

Click to view attachment
8-bit and 16-bit individual frames are here:

http://stevealbers.net/ast/mars/mc/

fredk

Sep 15 2022, 10:32 PM

This MSL navcam image:

https://mars.nasa.gov/msl-raw-images/proj/m...NCAM00558M_.JPG

was taken at around 20:24 LMST, when the sun was around 23 deg below the horizon according to http://www.greuti.ch/msl/clock_and_filenames.htm.

You can still see some twilight glow in the sky, as this low-pass filtered (and half-sized) version shows:
Click to view attachment
This view is towards azimuth 140 deg, and the sun was at azimuth 242 deg, so the brightening of the sky towards the right of the frame is consistent with a twilight glow.

On earth, twilight would be completely over well before this, when the sun is around 18 deg below the horizon. Do we expect martian twilight to last longer than earth's, given the dominance of dust scattering? The length of twilight will presumably depend on the atmospheric tau, though judging from the daylight images tau was fairly average on that sol.

climber

Sep 16 2022, 06:26 AM

Any chance it could be zodiacal light instead ?

nprev

Sep 16 2022, 08:04 AM

Likely has at least something to do with the scale height of Mars' atmosphere being a few km higher than that of Earth. Presumably that means that in addition to dust there are CO2 & H2O crystals at high altitude that would increase scattering & thus prolong twilight.

djellison

Sep 16 2022, 02:21 PM

QUOTE (climber @ Sep 15 2022, 10:26 PM)

Any chance it could be zodiacal light instead ?

Over a period of ~20mins from the first to last observation in that group, it fades to almost nothing.

So I presume it's a twilight phenomenon and not anything else.

scalbers

Sep 16 2022, 04:34 PM

As mentioned a longer twilight on Mars relates to two things that I would characterize as follows: A larger scale height compared with the radius of Mars. Also more dust relative to gas in the atmosphere (including the upper atmosphere). To get a good picture of all this it would be useful to make a plot of both gas and aerosol extinction coefficient for typical Earth and Mars atmospheres. These can be plotted with a Y-axis of planetary radii.

Bill Harris

Sep 19 2022, 03:25 AM

"Do we expect martian twilight to last longer than earth's, given the dominance of dust scattering?" (Fred)

I'd suspect more particulates (dust + CO2/H20) with a larger scale height (dustier and fluffier).

Uh, yes. What they said.

--Bill

scalbers

Apr 10 2023, 06:32 PM

Earth sky analogy to Mars:

https://www.scmp.com/news/china/science/art...ijing-mars-blue

scalbers

Jul 2 2023, 09:50 PM

For convenience is there a handy reference to find a solar ephemeris to list elevation angle and azimuth as seen from the various spacecraft on the surface of Mars? Thanks.

fredk

Jul 2 2023, 11:26 PM

The filename sites for MER and MSL are still up:

http://www.greuti.ch/oppy/html/filenames_ltst.htm
http://www.greuti.ch/msl/clock_and_filenames.htm

mcaplinger

Jul 2 2023, 11:43 PM

https://www.giss.nasa.gov/tools/mars24/

rlorenz

Jul 4 2023, 04:03 PM

QUOTE (scalbers @ Jul 2 2023, 05:50 PM)

For convenience is there a handy reference to find a solar ephemeris to list elevation angle and azimuth as seen from the various spacecraft on the surface of Mars? Thanks.

Mars24 as Mike posted is handy (There's a Titan24 too..)

A more powerful tool for generating tabulated solar system data generally is
https://ssd.jpl.nasa.gov/horizons/app.html#/

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