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I have a homebrew setting with a moon that has some specific features orbiting an Earth sized planet, and I'm trying to find out how these features would affect how the moon looks from the surface of said planet during the night.

It's a binary star system, with two sun-like stars roughly 1.5 AU apart surrounded by a cloud of argon gas. The planet has the same mass and atmospheric composition as Earth, and is roughly 4 AU away from the stars. The moon is essentially the same as Luna in every way, except that it has a large obsidian core with a thick layer of colorless and transparent petalite.

TL;DR: What does this moon look like at night?

Thank you for any help provided!

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    $\begingroup$ I think a cloud of gas next to a star (or 2 stars) would be blown away in the solar wind(s). I do not think it could persist floating next to them like some renegade atmosphere without a gravitational body to hang on to it. $\endgroup$
    – Willk
    Sep 1, 2017 at 11:20
  • $\begingroup$ A moon with a pure mineral see-through crust? Extremely cool, but this is no natural moon, I guess, right? $\endgroup$
    – pablodf76
    Sep 1, 2017 at 11:36
  • $\begingroup$ If the moon's surface is Petalite then it will appear as white — not transparent — from the surface of the planet. This is because it will only be transparent if it is an entirely smooth surface. By comparison remember that snow is actually comprised of ice crystals. Since the crystals of snow are structured they diffract and diffuse incoming light, meaning that the white appearance of snow is an illusion: what we are seeing is simply all light being diffusely reflected off of snow. Petalite moon crystals would do the same: diffuse incoming light to create a matte white appearance. $\endgroup$
    – MichaelK
    Sep 1, 2017 at 11:46
  • $\begingroup$ And no, even if the moon was created with a smooth flat layer of Petalite, it would not remain that way. Meteors would soon enough make the surface look like someone had been shooting at bulletproof glass. $\endgroup$
    – MichaelK
    Sep 1, 2017 at 11:50
  • $\begingroup$ Petalite is white and reflective, too, no? It would look like our moon. $\endgroup$
    – Mikey
    Sep 2, 2017 at 20:37

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I think the space argon would blow away in the solar wind.

I think the obsidian core would not affect how the moon looks, because it is on the inside. Maybe if there were a crater deep enough to unearth some of the obsidian it would be darker than adjacent moon, because obsidian is dark.

The surface of Luna is made of plagioclase feldspar. https://en.wikipedia.org/wiki/Geology_of_the_Moon

Lunar rocks are in large part made of the same common rock forming minerals as found on Earth, such as olivine, pyroxene, and plagioclase feldspar (anorthosite). Plagioclase feldspar is mostly found in the lunar crust, whereas pyroxene and olivine are typically seen in the lunar mantle.[15]

Feldspar is an aluminum containing mineral. Petalite is very similar and differs in that it contains lithium instead of potassium; I found petalite described as "lithium feldspar". The moon's surface is broken up into dust and tiny bits from impacts. When broken into tiny bits I do not think one can distinguish potassium feldspar from lithium feldspar by sight. Take a look.

feldspar powder petalite powder

As regards albedo and color I think the proposed petalite moon would look like Luna does now.

With one exception: this moon has 2 suns and so it would be lit from 2 angles, and so there would be 2 different crescents as the moon went through its phases: one crescent brightly lit by both stars, one dimmer crescent lit by just one star and the remainder dark and unlit. If anyone feels motivated to Photoshop 2 phases of the moon on top of each other, please feel free to add your image in an edit. MS Paint is not up to that job, it turns out.

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