Moon unusual geography/structures and how they are observed from a planet

Assuming a planet has a moon like Earth's how big something would need to be so it's visible from the planet? The fantastical structures I am thinking are:

Crystal "line" that circles around the moon's equator. I also want to know if it's orientation would meaningfully change through out the year and how that could be used for navigation.

Crystal domes, both with people living in them and those without. And would the city lights be visible when the domes are in the dark side of the moon?

Couple of kilometres wide, possibly less depending on it's relative reflectivity. It wouldn't change in orientation much, assuming that a similar orbital dynamic to Earth-Luna, they're tidally locked, meaning the lunar body is always presenting the same face to the planet, and at the same orientation.

As for visibility of things like cities, yes it would theoretically be possible to see them, but you'd actually get better views as the moon waxes and wanes. When it's new its up during the day and you have to contend with Earth-(or appropriate planetary body)-shine. But at local night (planetary time) you don't have to contend with that as much so any cities or towns lit by artificial lighting would stand out better.

Per this, the human eye, unaided, can resolve features on the Moon that are about 200 miles (335 km) across. The Moon is only visible from Earth (again, unaided) while illuminated by the Sun; otherwise it is too dark. The Sun would drown out any artificial illumination by several orders of magnitude.

I don't know how intense artificial illumination would have to be to stand out on the dark side of the Moon against the night sky, but given the scale, it'd probably have to be intentionally set up for that purpose, like the Luxor hotel and its space spotlight. I don't think you'd be able to see something on the scale of an Earth city with the naked eye, even with perfect conditions, unless it's putting out more light than any actual Earth city. Now, multiple cities all giving off light at night might be visible, barely.

Edited by Fighteer on Oct 8th 2018 at 11:50:22 AM

We're assuming unmodified human eyes here?

Yes. + these are useful.

Worth noting is that the Earth, while much brighter than the Moon and covering 16 times more area in the sky when seen from the Moon's surface, probably would not have visible human features, such as city lights, during its nighttime phase. In fact, the only hope you'd have of seeing them at all would be during the brief period of total night when the planet is completely dark. Even the slightest crescent of the day-side would be bright enough to drown out human lights. The same would be true of the Moon but more so.

I am imagining a future romantic moment in which two Earthlings are sitting on a hill out in the boonies at night with a new Moon, and carefully looking to see if they can pick out the surface lights from the lunar cities, followed presumably by sex.

Edited by Fighteer on Oct 8th 2018 at 2:12:44 PM