Make a printable month of approximate lunar phases.
Each day shows the approximate phase and illuminated fraction at 12:00 UTC. This simple mean-cycle model is for general observing plans; it does not calculate exact phase times, moonrise, visibility, or tides. Choose a month between 2000 and 2100.
Method and sources
Age is elapsed days from the 6 January 2000 new moon (18:14 UTC), modulo a mean synodic month of 29.53059 days. Illumination is (1 − cos(2π × age / month)) / 2. Actual lunations vary, so errors can exceed a day. Phase labels describe the nearest eighth of the mean cycle.
NASA: Moon phases, 1901–2000 supplies the reference new moon and mean month. For precise dates use US Naval Observatory moon phases.
Instructions
- Choose Month (UTC) between January 2000 and December 2100.
- Select Calculate to build the calendar.
- Review the daily phase labels and illumination, then use Download results or Print.
Understanding your results
Each square describes the approximate Moon at noon UTC. Illumination is the estimated lit fraction, so 50% means roughly half the disc is lit. It does not tell you whether the Moon is above your horizon or visible through cloud.
What to do if a phase is shown on a different day from another calendar
This uses an average lunar cycle and can differ by more than a day. UTC dates can also differ from your local date. Use the precise phase sources linked above when the exact timing matters.
Using this tool in your browser
This tool handles your entries in your browser with JavaScript enabled and does not save them automatically. Use the download or print controls described in the instructions to keep a copy before closing or reloading the page. On a phone, your browser controls where downloads go and which print options are available.
Summary
The calendar is useful for general observing plans and learning the sequence of phases.