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 Post subject: True color of Mar's sky
PostPosted: Sat, 16-01-16, 13:32 GMT 
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I have been noticing that more and more photos of Mars, supposedly in true color, have a blue/beige tint to the atmosphere. I know Hollywood is notorious for ignoring science, but in their recent movie, The Martian", their CGI folks gave the Mars sky a slight bluish tint. They consulted with three Mars experts at JPL in California to get the sky right. Below are some photos, taken from Curiosity and from the movie:

Attachment:
File comment: Curiosity photo in true color
PIA17944_Mcam-SOL538-WB-br2.jpg
PIA17944_Mcam-SOL538-WB-br2.jpg [ 166.98 KiB | Viewed 1565 times ]


Attachment:
File comment: CGI image from The Martian
Mars air.jpg
Mars air.jpg [ 227.87 KiB | Viewed 1565 times ]


The default atmosphere code for Mars shows a gray sky only with no hint of blue or beige. I have tried to edit the atmosphere ssc file but cannot seem to get the sky to appear slightly blue/beige near the bottom, fading to blue/gray higher up. Can anyone help me with this?

Frank


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PostPosted: Sat, 16-01-16, 13:58 GMT 
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There is another spectacular image by NASA that shows the famous
"Blue Sunset" on Mars
Image

http://www.jpl.nasa.gov/spaceimages/det ... d=PIA19401

This we can reproduce in Celestia/ celestia.Sci using Mie theory for scattering of light on particles in the Mars atmosphere. Therefore, a tad of blue in the daylight sky might well get amplified into a solid blue sky towards sunset.

Fridger

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PostPosted: Sat, 16-01-16, 14:03 GMT 
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Fridger:

Yes, that is great. Could you please post the Mie Atmosphere SSC code to achieve this? I have tried but cannot seem to get it right.


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PostPosted: Sat, 16-01-16, 14:07 GMT 
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This is as far as the Mie theory simulation goes:

Image

Need to dig for the corresponding parameter values...

We discussed these matters in a long thread of mine, here,
viewtopic.php?f=9&t=116
Manifestations of Atmospheric Light Scattering (Mie Theory) together with ChrisL.

The above image I made for Celestia 1.5.0 CVS, really a long time ago.

Fridger

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PostPosted: Sat, 16-01-16, 17:39 GMT 
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I have searched the big discussion thread from 2007 and cannot find a listing of the Atmosphere Mie Scattering parameters you used to produce the bluish photo above. Is this code what is now present in the default solarsys.ssc file in Celestia161? If so, I am not getting the same kind of tint on my Windows 10 system. The atmosphere is way too thin (I can see stars even in daytime).

If you've used a modified Mie scattering code of Mars for Celestia.sci, would you be willing to post it here for us?

Thanks

Frank


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PostPosted: Sat, 16-01-16, 18:21 GMT 
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fsgregs wrote:
I have searched the big discussion thread from 2007 and cannot find a listing of the Atmosphere Mie Scattering parameters you used to produce the bluish photo above. Is this code what is now present in the default solarsys.ssc file in Celestia161? If so, I am not getting the same kind of tint on my Windows 10 system. The atmosphere is way too thin (I can see stars even in daytime).

If you've used a modified Mie scattering code of Mars for Celestia.sci, would you be willing to post it here for us?


Sorry, I can't help you any further here. It's just too long ago and my Celestia records are considerably thinned out. I can assure you that future releases of celestia.Sci will indeed display a "Blue Sunset" on Mars. But as a matter of principle, there will certainly not be any partial releases of code to individuals...

Fridger

PS: There are actually more "Blue Sunsets" within our Solar system ;-)
[By all means click on image and then hit the browser fullscreen shortcut (F11 for FF)]
Attachment:
Blue_sunset_sunrise.jpg
Blue_sunset_sunrise.jpg [ 67.69 KiB | Viewed 1539 times ]

(simulated for Pluto with celestia.Sci)

Given the new Pluto data, we can be very sure about this matter.

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PostPosted: Sat, 16-01-16, 19:20 GMT 
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Fridger:

OK, thanks anyway. Do you have any feel for when celestia.sci will finally be available?

Frank

ps. Pluto, its sky and the Milky Way behind it looks spectacular! :)


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PostPosted: Sat, 16-01-16, 20:03 GMT 
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fsgregs wrote:
Fridger:

OK, thanks anyway. Do you have any feel for when celestia.sci will finally be available?


At least development will become public very soon. Since celestia.Sci is already very stable, experienced users will then be able to build pre-versions with little effort..

Yet, since our team is still small, the amount of code is very large and real life catches up frequently with all team members, an extrapolation of the first official release time is hardly possible.
Quote:
Frank

ps. Pluto, its sky and the Milky Way behind it looks spectacular! :)


Thanks.

If you are interested in the current simulation of the Pluto system, have a look here:
My best 16k Pluto texture...(for now)

Fridger

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PostPosted: Sat, 16-01-16, 21:43 GMT 
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Wow - the Pluto textures in celestia.sci are fantastic. Congratulations!

I will patiently await the official release of celestia.sci. I am almost 70 yrs old, so ..... ;)

Frank


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PostPosted: Sun, 17-01-16, 9:14 GMT 
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fsgregs wrote:
Wow - the Pluto textures in celestia.sci are fantastic. Congratulations!

I will patiently await the official release of celestia.sci. I am almost 70 yrs old, so ..... ;)

Frank


;-)

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PostPosted: Sun, 17-01-16, 21:10 GMT 
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Frank,

I found my notes about the Mie parameters for the BlueSunset on Mars.
Here they are:
Code:
Atmosphere {               
     # Blue sunset, as seen in true color pictures from Pathfinder
      Mie 0.001
      MieAsymmetry -0.15
      Rayleigh [ 0.0010 0.0006 0.0003 ]
      Absorption [ 0.003 0.002 0.001 ]
      MieScaleHeight 11
}

I made a little video with celestia.Sci, starting at daylight (check the sky color!)
and ending with the Blue Sunset (MP4 format)

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Changing skycolor of Mars from Mie Theory with Blue Sunset
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

You are welcome to use the video publicly, but please always with credits to the author...
There is certainly some more tuning possible, but as often spare time was too short.

Fridger

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PostPosted: Sun, 17-01-16, 21:54 GMT 
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Fridger:

Thank you. That sky is exactly what I was after. It looks most realistic. I appreciate your effort to find the code. :)

Frank


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