Skip to content
Lizely

Moon Phase Today

See the Moon's current geocentric phase angle, illuminated fraction, nearby primary phases, calculation time, and your browser time zone without sharing a location or making a runtime network request.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Open the tool and wait for the local calculation to show the current eight-stage label, phase angle, illuminated percentage, and nearby primary-phase events.
  2. 2.Read the calculation timestamp and resolved browser time zone; choose Recalculate whenever you want to sample a fresh browser instant.
  3. 3.Use the disclosed angle-band table to distinguish the convenient eight-stage label from the exact 0°, 90°, 180°, and 270° primary-phase instants.

About Moon Phase Today

Moon Phase Today calculates the Moon's phase for the current instant reported by your browser. It shows the geocentric ecliptic longitude difference between the Moon and Sun, the illuminated fraction, a convenient eight-stage display label, and the surrounding primary phase events. The calculation time and the time zone resolved by the browser are displayed with the result. The tool does not ask for location permission because a geocentric phase does not depend on the viewer's city. It also does not upload a date, contact a remote astronomy service, or require an account.

The calculation runs in the tool island with the precisely pinned astronomy-engine 2.1.19 package. A narrow internal adapter exposes only three operations needed here: validate the supported date, calculate the geocentric phase angle and illuminated fraction, and search for one of the four primary phase angles. The component does not call the package's broader vendor API directly. The package is MIT licensed, has no runtime dependencies, is shipped with the application rather than copied from a CDN, and is loaded only when this tool widget is requested.

Four primary phases have exact mathematical event meanings in this product. New Moon is the instant the geocentric phase angle reaches 0 degrees, First Quarter is 90 degrees, Full Moon is 180 degrees, and Last Quarter is 270 degrees. Those are instants, not multi-day labels. The result separately provides a broad eight-stage name for everyday display. That label is a Lizely convention created by dividing the angle circle at half-way points between the primary angles. It must not be read as an official United States Naval Observatory classification.

The eight bands are disclosed rather than hidden: New Moon covers 337.5 through 360 degrees and 0 through 22.5 degrees; Waxing Crescent covers 22.5 through 67.5; First Quarter covers 67.5 through 112.5; Waxing Gibbous covers 112.5 through 157.5; Full Moon covers 157.5 through 202.5; Waning Gibbous covers 202.5 through 247.5; Last Quarter covers 247.5 through 292.5; and Waning Crescent covers 292.5 through 337.5. Lower bounds are included and upper bounds are excluded, except that the angle wraps cleanly at 360 degrees.

Accuracy is bounded and testable. Twelve literal primary-phase timestamps were frozen from the official USNO Astronomical Applications API. They include New Moon, First Quarter, Full Moon, and Last Quarter examples; dates near the 1700 and 2100 limits; February 2020 in a leap year; and events that cross from December into January. Tests search the same phase with Astronomy Engine and require every result to differ from the minute-resolution USNO timestamp by no more than two minutes. USNO is used only for research and test fixtures. It is never called when a visitor opens or recalculates this tool.

The public input and output boundary is years 1700 through 2100 because that is the range covered by the USNO service used for the independent comparison. The current-time interface normally remains well inside that boundary. Results should be treated as educational astronomical estimates. The page does not claim second-level precision, observational-apparent timing for a particular site, professional ephemeris status, or suitability for navigation, photography safety, tides, religious observance, or other time-critical decisions. Atmospheric visibility, local horizon, weather, and moonrise or moonset are different questions and require location-specific data that this tool intentionally does not collect.

Recalculate uses a fresh browser instant, and an automatic refresh occurs once per minute while the widget is mounted. The current result remains fully available offline after the page assets have loaded. No external CDN, USNO runtime request, analytics-dependent computation, file upload, camera, GPS, cookie, or browser storage is needed for the calculation.

Methodology & sources

At the current browser instant, call a narrow local adapter around astronomy-engine 2.1.19 to calculate the geocentric Moon-Sun ecliptic longitude difference and illuminated fraction. Search locally for the surrounding 0°, 90°, 180°, and 270° primary events. Map the angle to eight Lizely display bands with boundaries at 22.5°, 67.5°, 112.5°, 157.5°, 202.5°, 247.5°, 292.5°, and 337.5°. Freeze twelve literal USNO minute-resolution primary-phase events spanning all four event types, a leap year, year boundaries, and the 1700–2100 limits; require Astronomy Engine to stay within two minutes. Never call USNO at runtime and never request location.

Frequently asked questions

Does this tool need my location?
No. It calculates the geocentric Moon-Sun phase angle for the current instant, so it does not request GPS or a city. Moonrise, moonset, horizon appearance, and weather are location-specific and are outside this tool.
Are all eight displayed phase names official USNO categories?
No. New Moon, First Quarter, Full Moon, and Last Quarter are exact primary angle events. The eight-stage labels use a fully disclosed Lizely angle-band convention for convenient display.
How accurate are the times?
The pinned engine is tested against twelve minute-resolution official USNO primary-phase records from 1700–2100, with a maximum accepted difference of two minutes. The result is educational and does not claim second-level or professional astronomical precision.

Related tools

Fortune & Divination guides

View all