Moon Phase Viewer
Look up the moon phase, illumination and moon age for any date, plus the next new and full moon.
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- Phase
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- Illuminated
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- Moon age
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- Next new moon
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- Next full moon
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- Lunation
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Upcoming phases
| Phase | Date & time (UTC) | In |
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All times are UTC and are astronomical estimates (accurate to within a couple of minutes), not medical, navigational or safety advice.
How it works
Pick any date and time and the viewer works out where the Moon is in its 29.53-day cycle: the phase name, the illuminated percentage of the disc, the Moon's age in days since the last new moon, and the exact times of the next new and full moon. The drawing next to the numbers is generated with the Canvas API — the terminator (the line between light and dark) is an ellipse whose width follows the illuminated fraction, so a 12 % crescent really is drawn as a 12 % crescent. Southern-hemisphere observers see the lit limb on the other side, so the hemisphere switch mirrors the image and the emoji.
The phase times come from Jean Meeus' Astronomical Algorithms (chapter 49): a mean lunation is refined with the periodic terms for the Sun's and Moon's anomalies, which brings each new, first-quarter, full and last-quarter moment to within a minute or two of published almanac values between 1600 and 2400. The lunation number is the Brown series used by astronomers, where lunation 1 began in January 1923. Everything is calculated in your browser with plain JavaScript — no API call, no location request, no ads and no sign-up — so the page keeps working offline and the date you look up never leaves your device.
Frequently asked questions
How accurate is this moon phase calculator?
The phase times come from Jean Meeus' Astronomical Algorithms (chapter 49): a mean lunation refined with the periodic terms for the Sun's and Moon's anomalies. Between 1600 and 2400 each new, first-quarter, full and last-quarter moment lands within a minute or two of published almanac values. All times are shown in UTC, so no location or timezone guess is involved.
What does the moon age in days mean?
Moon age is the time elapsed since the last new moon. A full lunation (new moon to new moon) averages 29.53 days, so an age near 0 is a new moon, around 7.4 days is first quarter, around 14.8 days is full, and around 22 days is last quarter. The viewer shows the age to one decimal alongside the illuminated percentage of the disc.
Why does the moon look flipped in the southern hemisphere?
Observers south of the equator see the Moon rotated by roughly 180 degrees, so a waxing crescent that is lit on the right in Europe or North America is lit on the left in Australia or Chile. Switch the hemisphere selector and both the drawn moon and the phase emoji are mirrored to match what you actually see in the sky.