How long can a moon remain non-spherical, and what might it look like when full?

I'm trying to "build" a world in which the moon is always visible at night, and only at night, to the majority of areas on that world. I've been told that an L2 Legrange point could be a viable configuration for this to be true, and that essentially means that the moon orbits the world at the same rate that the world orbits its sun, and remains constantly on the opposite side of the world from the sun. I am unsure as to the moon's direction of orbit and direction and rate of spin.

It seems that this configuration would result in the moon always appearing full, so I was thinking of ways for it to appear as a crescent while actually being "full" and still fitting the other conditions. I'm wondering if a moon that is not a true sphere, but rather a spherical crescent might work, as I expect it would have close enough orbital mechanics to work out mostly the same. I imagine that if it spins in the right direction at the same rate that it orbits the world, it could always appear as a crescent.

I have many questions, but the most important is: Is this viable, and if so, for how long? Will the orbit likely decay or will the moon become a sphere again (in my mind, it was carved by some sort of collision), and how long would both take if so?

I'm guessing the answer will change depending on the size, distance, etc. of all objects involved (moon, world, and sun). Perhaps the moon can be small enough that its own gravity won't cause it to reform as a sphere at all, and if so, can it still be big enough to be seen as a disc in the sky on a world that is habitable by humans and other life? Can a world of an appropriate size be sufficient for its own plant and animal life to have evolved by the point humans find it? And would anything else have to be specific, like the world's axial tilt or its ratio of days to a year?

I'm new to this, and any input would be greatly appreciated!

posted almost 6 years ago

Correnon‭

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