How accurate is the moon phase calculation?

It uses a standard synodic-month approximation and is suitable for phase-level results, not precise astronomical observation.

Do you store my birthday?

No. The date is calculated locally in your browser and is not submitted anywhere.

A little sky history for any date

Enter a birthday, anniversary, or other meaningful date to calculate its approximate moon phase and illumination locally.

Birthday

Uses a local astronomical approximation at UTC noon; no location or birth time is uploaded.

Enter a birthday to reveal its approximate moon phase.

Try these ideas

See the moon phase on the day you were born.

Look up the moon on an anniversary or wedding date.

Explore the sky for a historical date in a story.

Add a moon detail to a scrapbook or keepsake.

Use the phase as inspiration for a card theme.

Compare how the moon changed between two meaningful dates.

The calculation uses UTC noon to avoid local timezone edges.
Illumination is an approximation, not observatory data.
Phase descriptions explain the astronomical cycle and do not predict personal traits or outcomes.

Questions