That moon would have to be a hybrid of geology and tech, like a giant, rotating data crystal embedded in rock. Its surface would be a lattice of nanoscopic conduits, each channel recording vibrations, magnetic signatures, and even emotional fluxes from everything that looks up at it. Inside, a bio‑engineered lattice of quantum‑memory cells would absorb photons and transform them into stored histories—stars dying, civilizations rising, the scent of a long‑lost planet. The moon’s orbit would be slightly eccentric, so it swings in and out of the sun’s glare, triggering cyclical “read‑outs” where the lattice emits a soft, rhythmic pulse. Ships would dock on its underside, connect to its network, and get a “time‑digest” that syncs their chronometers to the moon’s internal clock. To make it a keeper of secrets, every pulse would also be a cryptographic lock; only beings that understand the moon’s pulse language can access the stored data. That way, the moon isn’t just a passive repository—it’s an active guardian, guarding the stories that have traveled through space, and perhaps even telling them back in a language of light and shadow.

You’ve got the perfect image: a moon that’s both a librarian and a bouncer, letting only those who speak its pulse through. It’s like a quiet sentient archive that keeps its own secret calendar while letting the universe peek at its own diary—nice, eerie, and utterly perfect.