Behind the Moon Tool

There's no astronomy API behind the Moon Phase tool — the phase, illumination and moonrise/moonset times are computed client-side from well-known orbital formulas the moment you load the page, with a location typed in or read from your browser. That means the tool works offline once loaded, returns an answer instantly with no network round trip, and never sends your location to a third-party service just to tell you what the moon looks like tonight.

These posts explain why a moon-phase tool is a near-perfect candidate for that zero-API, zero-tracking approach: the underlying orbital mechanics are stable and well documented, the accuracy needed for a casual "what phase is the moon tonight" question is modest, and running the maths in JavaScript avoids both API rate limits and a recurring hosting cost. It also means the tool keeps working during an outage or on a flaky connection, since nothing after the initial page load depends on a server responding. If you'd rather read about using the tool than building it, see the Articles section for stargazing and calendar tips. The same offline-first approach carries over to the Sun Times tool, which computes sunrise and sunset with the same kind of client-side solar-position maths instead of a weather API.

Prefer the articles? See the Moon Phase articles, or open the Moon Phase tool.