Moon Phase Calculator
Find the phase of the moon for any date.
The moon's changing face
The moon cycles through its phases — new, crescent, quarter, gibbous, full and back — over about a month, and this finds the phase for any date. It is useful for photography, gardening lore, stargazing, or simple curiosity about the night sky.
Enter a date to find the moon phase.
Why the moon has phases
The phases happen because we see the moon lit by the sun from different angles as it orbits Earth — the moon does not produce its own light, so we see only the portion the sun illuminates from our viewpoint, which changes through the cycle. A full moon is when Earth sits between sun and moon so we see the whole lit face; a new moon is when the moon is between us and the sun, its lit side turned away. The full cycle takes roughly twenty-nine and a half days, which is where the rough length of a month comes from. Knowing the phase is genuinely practical for planning night photography or stargazing, since a bright full moon washes out faint stars, while a new moon gives the darkest skies. It is also just a lovely thing to be aware of.
Frequently asked questions
Why does the moon have phases?
Because we see the sun lighting it from different angles as it orbits Earth — we see only the illuminated portion, which changes through the cycle.
How long is the full cycle?
Roughly twenty-nine and a half days, which is where the approximate length of a month originally comes from.
Is anything uploaded?
No. The calculation happens in your browser.