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Moon Phase Tonight

See tonight's moon, or the moon on any date from 1900 to 2100: the phase by name, how much of the disc is lit, how many days it is into its cycle, and how long until the next full and new moon. The disc is drawn to the actual illumination and a hemisphere switch flips the lit side for the southern half of the world. Everything is computed in your browser from the mean lunar cycle, so nothing is fetched and nothing goes stale, and the month's principal phases are listed underneath.

TonightMoon phaseReading tonight's date from your clock.
Date
Hemisphere

The date is read as nine in the evening, your local time. The next-phase times and the month table are in UTC. The hemisphere switch mirrors the disc: south of the equator the same moon is lit on the other side.

One moon, one phase, everywhere. The whole planet sees the same phase on the same night, because the phase is set by where the moon is in its orbit, not by where you stand. What changes with location is the tilt of the lit part and, south of the equator, which side it is on. The phase, age and illumination are computed from the mean lunar cycle, which lands each new or full moon within about half a day of the almanac: usually on the same day, occasionally on the neighbouring one when the true instant is near midnight. For the exact minute of a phase, an ephemeris is the source.

Common questions

How is the moon phase calculated?
From the mean lunar cycle. One new moon follows the next every 29.530588853 days on average, so the tool counts the days since a reference new moon on 6 January 2000, takes the remainder, and that remainder is the moon's age. The lit fraction is half of one minus the cosine of the age as a fraction of the cycle: zero at new, one at full, a half at both quarters. The named phase comes from the age: New moon, First quarter, Full moon and Last quarter each own the day either side of their instant, and Waxing crescent, Waxing gibbous, Waning gibbous and Waning crescent fill the gaps. It runs entirely in your browser and needs no data that could go out of date.
Why is the time of the full moon a few hours off from my almanac?
Because the real moon does not keep to the average. Its orbit is an ellipse that the sun keeps pulling on, so a single cycle can be up to about seven hours shorter or longer than the mean, and a new or full moon can land up to about half a day away from where the mean cycle puts it. That is why the hour here is shown rounded and marked as around. The day is usually right and the hour is within about half a day, and if you need the minute, an ephemeris or an almanac is the source, since it carries the corrections this tool deliberately leaves out.
What does the hemisphere switch change?
Which side of the disc is lit. From the northern hemisphere a waxing moon is lit on the right and a waning moon on the left. From the southern hemisphere you are looking at the same moon from the other side of the Earth, so it appears turned round and a waxing moon is lit on the left. The phase, the percentage lit and the age are identical in both settings: the switch only mirrors the drawing so that it matches your sky.
Does the moon look different from where I live?
No. The whole planet sees the same phase on the same night, because the phase is set by where the moon is in its orbit around the Earth, not by where you stand on it. What changes with location is the orientation: how the lit part is tilted, and in the southern hemisphere which side it is on, which is what the hemisphere switch handles. The moon also rises and sets at different local times, so the date on which a phase falls can shift by a day across time zones, which is why the next-phase times and the month table here are labelled in UTC.
What does the moon's age mean?
The number of days since the last new moon. A new moon is age 0, the first quarter is about 7.4 days, the full moon is about 14.8 days and the last quarter is about 22.1 days, and the cycle wraps back to 0 after 29.5 days. The age shown here is for nine in the evening, local time, on the chosen date, because the question is tonight's moon and the phase only moves about three percent of the cycle over a whole day.
Why does the tool only cover 1900 to 2100?
The mean cycle is anchored to a new moon in January 2000, and its accuracy has been checked against real eclipses, which pin a new or full moon to the minute, within a few decades of that anchor. The average length of the month is very stable, so the cycle would probably still be close well outside those two centuries, but the tool does not claim what it has not checked.

The phase, age and illumination are computed from the mean lunar cycle, which lands each new or full moon within about half a day of the almanac: usually on the same day, occasionally on the neighbouring one when the true instant is near midnight. For the exact minute of a phase, an ephemeris is the source.