The Martian Sky Options

[Bjorn Jonsson]

I have been attempting to make computer generated images of the Martian atmosphere, both as seen from the surface and from space. To check the results I have been looking for spacecraft images to use as ground truth. I have found lots of images - by far the best ones I have found are from UMSF in this thread: http://www.unmannedspaceflight.com/index.php?showtopic=3324

However, I'm always looking for more ;-). So if anyone knows of more and/or better images I'm interested in them. What would be best are mosaics showing the sky from the horizon (with the horizon/surface visible) and towards the zenith.

The sky varies a lot because of variable amount of dust but the general impression I get is that the sky is bright near the horizon (usually brighter than the surface) but gets much darker higher in the sky. There is probably a fairly large, bright area in the sky near the sun, possibly less reddish (lower R/B ratio) than parts of the sky farther from the sun.

I'm already getting fairly interesting results, this one has a field of view of 90 degrees:


(needless to say this one is 'overexposed' near the horizon; dynamic range is sometimes a problem)

The problem is that even though this may not be bad the limb currently appears far too bright as seen from space :



This shows that my atmospheric model is erroneous in some way - I suspect that as seen from the surface the Martian sky is darker high above the horizon than I have been assuming.

[scalbers]

I've seen Jupiter at 10:20am from a high desert location, right next to the moon (as documented in an ancient issue of Sky and Telescope). There is a case to be made that Sirius would be visible from a clean air location when it is at the zenith and I recall some sightings have been made (I can dig out a paper on this).

For Mars it seems that daytime stars might be similar to Earth. The atmospheric scattering (and optical depth) is quite a bit greater and more than compensates for the dimmer sun. Yet aerosols have a greater angular dependence than gases, so away from the sun the sky brightness would tone down a fair amount. Extinction is more of a factor on Mars.

Mars being closer to Jupiter mostly applies near opposition. Daytime signtings would be closer to quadrature when there can be both a distance and a phase angle disadvantage impacting the apparent magnitude. Based on a review of the above sky simulations (assuming an optical depth of 0.5) I may be able to calculate the zenithal limiting magnitude for various solar elevation angles. The best part of the sky to look would be somewhat lower than the zenith and opposite the sun in azimuth.