Brown dwarf textures

[ajtribick]

Some 1K brown dwarf textures:

L dwarf texture
T dwarf texture

These can be used in .stc and .ssc files - they are also public domain, so feel free to edit/modify.

[eburacum45]

You have definitely gone for the magenta look with that T dwarf; nice.

Some interesting discussion of this colour here
http://www.bautforum.com/showthread.php ... ht=MAGENTA

[ajtribick]

That's an interesting discussion, I was also sceptical about whether T-dwarfs could be magenta (but hey, it was Grant who suggested I make these as a follow up to my Sudarsky giant planets, so I went with his magenta suggestion), that page seems to make the case pretty convincing.

Talking of my Sudarsky giant planets add-on, I may have to add a few bits to it, someone claims that Worlds Without End gives some extra refinements to the scheme, including methane clouds at 50-85K and ammonium hydrosulphide clouds at 150-200K.

However I'm going to have to get my hands on a copy before I make changes of that kind.

[eburacum45]

You could try ordering a copy from the local library; it might be expensive if they have to order it though.

[selden]

"Interlibrary Loan" is free in the U.S.

[Malenfant]

Dang. That thread on the BAUT forum is rather technical, but I notice that they're talking about how the eye sees the colour a lot. To which I have to ask, is that actually relevant at all?

After all, we know that a given wavelength of visible light equates to Red, or Blue, or Green or whatever. Shouldn't we be just be looking at the spread of wavelengths emitted by a T dwarf and then averageing them out somehow and saying something like "it's mostly in the IR and red and much less in the bluer wavelengths, so it's going to look red? Otherwise we have to take into account the sensitivities of every optical receiving device (eye, cameras, etc) when describing colour.

[Ryan McReynolds]

Talking of my Sudarsky giant planets add-on, I may have to add a few bits to it, someone claims that Worlds Without End gives some extra refinements to the scheme, including methane clouds at 50-85K and ammonium hydrosulphide clouds at 150-200K.

However I'm going to have to get my hands on a copy before I make changes of that kind.

That was me over at Extrasolar Visions.

I could transcribe the section of the book about the clouds. It's a whole whopping five paragraphs or so, no big deal. A great book and worth reading, but for the purposes of this specific discussion, it's not really necessary to go through the trouble of getting it.

I'll post again in a bit.

[Ryan McReynolds]

John S. Lewis, Worlds Without End, page 109. I was off, it's actually only three paragraphs!

What about gas-giant planets that find themselves in orbits that force unusually high or low temperatures on them? Excursions to lower temperatures will produce bodies with all the chemical simplicity of Neptune or Uranus: atmospheres of hydrogen, helium, and neon, possibly containing argon and methane if they are as warm as fifty-five or sixty degrees. Cloud-top temperatures below fifty Kelvins would freeze methane and argon out of the atmosphere, leaving only hydrogen, helium, and neon. Since helium, neon, and argon are virtually impossible to detect by remote observations, such a planet would appear as a dark blue, cloud-free, featureless ball of hydrogen gas. As light from its sun penetrates the planet's atmosphere, the short-wave light would be wiped out by scattering, and long-wave (red and infrared) light would be absorbed by the cold, dense hydrogen gas.

Gas-giant planets much warmer than Jupiter are certainly conceivable, and might be quite interesting bodies. Suppose that the luminosity of the star and the distance were just right to set the temperature of the planet's surface at 180 K. The internal heat source of the planet would raise this modestly to about 200 K. Then ammonia clouds would not condense, except perhaps in the immediate vicinity of the poles. The topmost cloud layer would be ammonium hydrosulfide, which, exposed directly to almost unattenuated ultraviolet light, would be stained a deep orange-brown by photolysis. Fresh new clouds would be shades of yellow and orange. Red features made of phosphorus are unlikely, since they would probably be overwhelmed by sulfur. Large breaks in the ammonium hydrosulfide clouds would expose pale bluish cloud systems made of water and ice.

Warming the planet further to 230 or 250 K would effectively dispel the ammonium hydrosulfide clouds, leaving a dense water-cloud layer directly exposed to sunlight, constantly seeded by photochemical products of methane, ammonia, phosphine, and hydrogen sulfide. The water clouds would be a seething hotbed of chemical activity. Further warming to 320 or 350 K would completely dispel the water clouds, leaving the atmosphere devoid of opportunities for water-based chemistry. Even higher temperatures are conceivable, but the biological interest of such bodies is greatly diminished by the absence of liquid water, which is essential to familiar organic chemistry.

And that's the extent of the book's commentary on hypothetical gas giant atmospheres. Make of it what you will.

[danielj]

Very nice.The only thing lacking is someone creating an ssc of these textures.I don??t have accurate information to create one.I put the two textures in the med res folder and the T dwarf didn??t change your appearance.

Some 1K brown dwarf textures:

L dwarf texture
T dwarf texture

These can be used in .stc and .ssc files - they are also public domain, so feel free to edit/modify.

[ajtribick]

Very nice.The only thing lacking is someone creating an ssc of these textures.I don??t have accurate information to create one.I put the two textures in the med res folder and the T dwarf didn??t change your appearance.

Well, you could always add a Texture declaration to some of the stars in nearstars.stc to try them out - there are several T dwarfs defined there, and Alula Australis Bb is an L dwarf.

To incorporate these in Celestia would require modifying the default star texture code. As I said, it was Grant who suggested that I make these to improve Celestia's depiction of brown dwarfs - so such code may be incorporated in some future version.

Otherwise we have to take into account the sensitivities of every optical receiving device (eye, cameras, etc) when describing colour.

If you're going for a "true colour" approach, it's probably best to deal with the colour sensitivity of the human eye. The problem with your averaging approach is that it doesn't help when rendering the scene, though it's probably ok for qualitative comparisons of colours.

And that's the extent of the book's commentary on hypothetical gas giant atmospheres. Make of it what you will.

Hmmm... I guess I won't be updating that add-on any time soon if that's all there is. Thanks anyway.

"Interlibrary Loan" is free in the U.S.

Wow, free interlibrary loans, cheap petrol, why am I still in the UK?

[eburacum45]

I might take advantage of the fact that my missus works at the BL in Wetherby to get hold of some of these books; Martyn J Fogg's Terraforming is my first priority though.

[WildMoon]

Wow, free interlibrary loans, cheap petrol, why am I still in the UK?

Not any more my friend, not any more. Atleast where I am in the U.S. for now.

[ajtribick]

Wow, free interlibrary loans, cheap petrol, why am I still in the UK?

Not any more my friend, not any more. Atleast where I am in the U.S. for now.

Hmmm... given that UK petrol prices are currently over 90p per litre, you'd have to have a price higher than $6.10 per gallon before you can claim expensive petrol prices.