Lunar Phase Calendar

Understanding Lunar Phases

The lunar cycle: The Moon completes one full cycle of phases — from New Moon back to New Moon — every 29.53 days (the synodic period). This calendar uses the Skyfield astronomy library to compute precise illumination and phase angles directly from JPL ephemeris data, so percentages and phase labels are accurate to the minute.

Rise and set times: When a ZIP code is provided, the calendar adds local moonrise and moonset times for each day. These times vary significantly with latitude and can shift by more than an hour across the continental US. On some days the Moon may not rise or set at all — this is normal near the poles or when the Moon's orbital geometry keeps it above (or below) the horizon for a full day.

Related space tools: Find out if tonight is good for stargazing — including twilight windows, satellite passes, and a quality rating — with the Night Sky Planner. Track the ISS in real time with the ISS Tracker, or predict visible passes for dozens of other satellites with the Satellite Pass Predictor.