As I see it may be a planned but not just yet implemented feature, but I just want to be sure.
In the book, every constellation entry shows a set of mini-pictures of moon phases. But it's the same for all constellations. Is it a bug, a design thing or it will be implemented in the future?

It's gonna be changed soon anyway as the constellation-section will be reworked.

The constellation details-section is reworked and it'll be changed in the next update.