Hi! I've noticed that Circa (Ring world) say "It's always day here" in the description, however, the day/night cycle is still present with default length (7 minutes). It's a bit annoying since you're supposed to rely on solar power. If this is a bug, this is what I've found:
I've noticed in planet surface properties you have ["day-night-cycle"] = 0 - however, it appears Factorio doesn't support this (minimum is 1 when changing it in Editor).
However, I believe you should be able to set always_day to true to fix this (https://lua-api.factorio.com/latest/classes/LuaSurface.html#always_day).
Same issue is present for Neumann V (Shipyard) (though I am not sure if that one should always be daytime as well).
If it's not a bug, I'd suggest altering the description.
Cheers!