We started PlanAstro from inside the amateur-astronomy and astrophotography community — the kind of people who build and adapt their own equipment, compare methods across forums and clear nights, and expect to be able to check a claim rather than take it on faith. That shapes the project more than any feature list does.

An observation session, not just an image

The object PlanAstro is built around is the observation session, not the picture that eventually comes out of it. A plan is an intention: a date, a place, an equipment profile, a set of targets you'd like to reach. A session is a fact: what actually happened that night, recorded through a short debriefing — executed, partial, or abandoned — once the night is over. Moving from one to the other is a deliberate step, not something the app assumes for you. A session can also start on its own, with no plan behind it: a plan is an accelerator, never a prerequisite.

This separation matters because a plan and a memory serve different purposes. The plan protects the night ahead — a horizon mask, a minimum altitude, lunar separation, mount-safety restrictions. The session is the honest record of what your equipment and the sky actually gave you, which is also what a later gallery publication, if you choose to make one, is built from.

Open by default, not as a marketing gesture

Astro Portal Core, the public repository behind PlanAstro, is not a trimmed-down "community edition." It is the self-hosted core of the exact same product: the gallery, the shareable target pages, the observation planner, the local deep-sky catalogue, the self-hosted light-pollution estimate. Whatever ships in that repository also ships in the free hosted tier, for good — no feature is ever pulled out of the open-source code to be sold separately later.

Trust, though, is not just a license file. It comes from documented formats, complete exports, unmodified original files, reproducible calculations, sources and licenses stated explicitly, no hidden telemetry, and a practical way to leave the hosted service if you ever want to. The Open source page has the license and the self-hosting quick start; the Offers page states, in the same terms as the project's own direction document, exactly what stays free forever and what a subscription pays for.

What this blog is for

We are not going to fill this space with announcements. When we publish here, it is because we have a method to show, numbers you can check against a script in the repository, and limits we are willing to state plainly. The first one of those, on calibrating the sky-brightness estimate against real measurements in Japan, is already up.