I created a world and had started on Astral Sorcery, and had all the constellations learned in about 5 hours. I saved and quit the world, but when I came back, the constellations weren't visible. I checked my tome and it said I had learned those constellations, despite them not showing up.
I made a new world to test this out, and once I restarted the world, the constellations disappeared.
Versions:
Astral Sorcery: 1.8.5
Minecraft: 1.12.2
Forge: 14.23.2.2618
Please let me know if you need more information do diagnose the problem or perscribe a solution, I'll try to reply as soon as possible.

Have you tried logging back into that same world after restarting MC itself, not just saving and quitting the world?

Just did, the constellations are still gone. Could it be a mod conflict? I have about 50 mods installed.
Would a list of the mods help?

Might help see if there's anything that stands out.

What about shaders or optifine?

Yes, I have optifine. Does the twinkling stars effect it adds affect the constellations from AS?
I turned the sky effects off, and now I can see the major constellations (Discidia, Armara, etc.) but not the minor ones.

Heck, i'm a fool. Just realized that the clouds from my shader pack were covering up the minor constellations. That was likely the root of the problem. Thanks for your time, Doomgull.