About MoonTonight

MoonTonight answers one question: what is the Moon doing tonight, and is it worth looking up? It shows the current phase, illumination, whether it’s a full Moon, moonrise and moonset, how the Moon is actually tilted in your sky, whether it’s above or below the horizon right now, and a countdown to the next major phase — without requiring an account or asking for your exact location before you choose to share it.

Methodology

Every phase, illumination, and rise/set figure on this site is calculated locally by astronomy-engine, an open-source astronomical calculation library tested against JPL ephemerides. There is no external astronomy API, no API key, and no network call behind these numbers — the calculation runs entirely in code, the same way on every visit.

A phase name is assigned to each calendar date using the Moon’s phase angle at local clock noon, with one deliberate exception: if the exact moment of a New Moon, First Quarter, Full Moon, or Third Quarter falls anywhere within that local calendar date, that event’s name is used for the whole day — regardless of what the noon angle alone would suggest. This is why “full Moon” status is never inferred from a rounded illumination percentage: 99% illuminated is not necessarily a full Moon by this rule, and 100% shown the day before or after the exact event isn’t either.

Illumination is stored internally at full precision. On the homepage and city pages it’s shown live, to 2 decimal places, recomputed every minute so it visibly moves rather than sitting frozen for the whole day — the phase calendar’s per-day figures round to the nearest whole percent instead, since a monthly overview has no single “right now” to be precise about. Either way, the displayed number is never used on its own to decide the phase name.

By default your location is guessed from your browser’s own time zone alone — no permission prompt, no GPS — matched against a curated list of cities. That location drives moonrise and moonset, and also the Moon graphic’s real tilt and the above/below-horizon curve beneath it: both are computed for your actual position and the current moment (using the standard bright-limb and parallactic-angle formulas), not a fixed left/right convention, and update automatically every minute. You can search for any city or place by name, or share your precise GPS location, for a more exact result. Searching the curated list is instant and entirely local; searching beyond it sends your search text (not your GPS location) to OpenStreetMap’s Nominatim geocoding service to resolve it to coordinates. Either way, your chosen location is only ever stored in your own browser, never on a server.

What “tonight” means here

“Tonight” is defined as the current local calendar date, not the window from sunset to sunrise. For the vast majority of visits this is exactly what you’d expect — but checking right around local midnight can, very rarely, feel one step off, since the calendar date (and therefore the phase name shown) changes at midnight rather than at sunset. A sunset-aware boundary would need solar calculations in addition to lunar ones; it’s a reasonable future refinement, not something this version needs to get right.

Supermoons, Blue Moons, and lunar eclipses

A supermoon is a full Moon that happens to occur close to perigee — the Moon’s closest approach to Earth in its elliptical orbit — making it appear modestly larger and brighter than usual. There’s no single official threshold; this site uses a common, round, widely-cited one: a real geocentric distance of 360,000 km or less at the exact moment of the full Moon.

A Blue Moon here means the second full Moon within the same calendar month, in UTC — the common modern definition (not the rarer traditional “fourth full Moon in a season” one). That classification always uses the shared UTC calendar month, worldwide, so which month a full Moon counts toward doesn’t depend on where you’re standing — even though the full Moon schedule itself shows each date and time in your own local time.

Lunar eclipses come in three real kinds: Penumbral (the Moon passes only through Earth’s outer, lighter shadow — a subtle dimming that’s genuinely hard to notice with the naked eye), Partial (part of the Moon crosses into Earth’s darker inner shadow), and Total (the whole Moon does — popularly called a Blood Moon, for the reddish color sunlight bent through Earth’s atmosphere gives the fully eclipsed Moon). Unlike a solar eclipse, a lunar eclipse is visible from the entire night side of Earth at once, so no specific location matters — only whether it’s nighttime where you are. The homepage only calls out a Partial or Total eclipse as “worth looking up”; Penumbral eclipses are still listed honestly on the full Moon schedule, just not flagged there, since going outside for one would show you almost nothing.

Limitations

This is a rough-and-precise tool, not a substitute for a professional ephemeris or observatory data. Moonrise and moonset depend on the exact location and can be genuinely unavailable on a given date near the poles, where the Moon may not rise or set at all — in that case this site says so plainly rather than showing a generic error. Searching for a place beyond the curated city list depends on a third-party geocoding service, so it can occasionally be slower than the instant curated search, or briefly unavailable.