About
Today’s Moon Phase is designed to give you professional-grade lunar information in a way that is clear and easy to use. We show you the Moon’s current phase and illumination, moonrise and moonset times, moon age and distance, altitude and azimuth, and even the Sun’s altitude for context.
How we calculate
Our astronomical calculations are powered by Astronomy Engine, an open-source astronomy library by Don Cross. Astronomy Engine is based on well-tested astronomical models such as VSOP87 and NOVAS C 3.1, and is designed to be accurate to within about one arcminute (1/60 of a degree). Its calculations are tested against trusted reference sources, including NOVAS and JPL Horizons. Using this library, we calculate the apparent positions of the Sun and Moon, lunar phases, illumination, moon age, distance, altitude, azimuth, moonrise, and moonset times for each observer’s location.
- Positions and phases: We use the apparent positions of the Sun and Moon to determine the Moon’s phase, illumination, age, distance, altitude, and azimuth.
- Rise and set times: We calculate moonrise and moonset based on the Moon’s apparent position for the observer’s location, with horizon-based calculations and atmospheric refraction corrections, so the results better match what you can actually see from the ground.
Astronomy Engine is licensed under the MIT License. Copyright © 2019–2025 Don Cross.
Accuracy and limits
We put accuracy first, but it’s important to know the limits:
- Atmosphere matters: Local weather conditions affect refraction, which can shift observed rise/set times by a few minutes.
- Near the horizon: Because the Moon rises and sets at a shallow angle, even small changes in conditions can make the timing vary.
- Location detail: Map position accuracy and your local horizon (mountains, trees, buildings) can also affect what you see.
Our rule of consistency
On most days, key values such as phase, illumination, distance, and age are calculated for local noon (12:00) in your time zone. On major phase days (New Moon, First Quarter, Full Moon, Last Quarter), the illumination values are shown for the exact moment the Moon reaches 0%, 50%, or 100%. Only on those dates do we use the actual event time for illumination, while all other values remain tied to local noon for consistency.
Why this matters
By combining scientifically validated methods with clear rules, our results closely match professional astronomical sources while remaining easy to understand. This way, you get information that is not only reliable but also practical for planning observations or simply following the Moon.
Who maintains this site
Today’s Moon Phase is operated by Ian Web Labs and created by Ian Kim. He maintains the site’s calculation logic, data presentation, and user experience, with the goal of making reliable moon data easier to understand and use.
We regularly review and update the service when the astronomy library changes, when reliable references suggest an improvement, or when we find a clearer way to present the data.
We want Today’s Moon Phase to be a reliable reference for anyone checking the Moon’s phase, timing, or position.