Moon Phase Tonight in New York and the Next Full Moon

Moon phases by date: the full lunar atlas

One lunar cycle, new moon to new moon, averages 29.53 days, yet any single cycle can run from 29.26 to 29.80 days, according to the phase catalog of Fred Espenak, the retired NASA eclipse expert. That spread is why a calendar built on the average can be off by as much as 18 hours. This calculator works out the real instants of every new moon, quarter and full moon for any date in the twentieth and twenty-first centuries, places them on the clock of your time zone, and shows how much of the disk is lit at the hour you choose.

29.53 days

average new moon to new moon

27.322 days

one orbit around the Earth

2 minutes

largest gap from the Espenak catalog

Four choices and the Moon is placed

Date - any day in the twentieth or twenty-first century: tonight, a birthday, a wedding, a planting day.
Time of day - the hour at which the lit percentage is taken, in three-hour steps. For a night sky question, 9 PM or 12 AM is the natural pick; even near a quarter, where it changes fastest, the lit share moves only about 1.3 points in three hours.
Time zone - twelve zones, from Hawaii to Sydney, with daylight saving applied automatically. It decides on which calendar day each phase lands.
Planting tradition - optional. Yes adds the planting-by-the-Moon guideline for the current half of the cycle, clearly labeled as folklore.
Read the result - the phase name, lit percentage, Moon age in days, the next phase, the next full and new moon, and a table of every principal phase in that month.

What changes from night to night, and what does not

Half of the Moon is always lit by the Sun. What changes is how much of that lit half faces us. At new moon the Moon sits roughly between the Earth and the Sun and shows its dark side; at full moon it is on the far side of the Earth and shows its whole lit face. NASA names eight phases in order: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third (last) quarter and waning crescent.

Only four of them are moments. New moon, first quarter, full moon and last quarter are instants that astronomers time to the minute, and they happen at the same instant for the whole planet. The other four are stretches between those instants. That is why a full moon can be on the 26th in New York and on the 25th in Los Angeles: the instant is shared, the calendar date is not. The calculator follows the convention of printed calendars and names a day after a principal phase when that phase falls on it in your zone.

"Quarter" trips people up. A first quarter Moon is a quarter of the way through the cycle, but the disk is half lit, about 50%. The lit share is not linear in time either: it climbs slowly near new moon, fastest around the quarters, and slowly again near full, which is why the Moon looks full for a couple of days.

The times come from the phase algorithm in Jean Meeus's Astronomical Algorithms, corrected from dynamical time to clock time with the NASA polynomial for Delta T. Against the 9,895 phases the Espenak catalog lists for those two centuries, every one matched in kind, the average gap was 0.2 minutes and the largest 2 minutes.

Eight phases, from dark disk to full face

Moon ages are averages for a 29.53-day cycle. The rise and set patterns are the ones NASA gives for most latitudes; for exact moonrise at your location, a local almanac is the right tool.

Phase	Lit share	Moon age	When it is up
New moon	0%	0 days	Rises and sets with the Sun, not visible
Waxing crescent	0 to 50%	0 to 7.4	Rises after sunrise, sets after sunset
First quarter	50%	7.4	Rises around midday, sets around midnight
Waxing gibbous	50 to 100%	7.4 to 14.8	Rises in the afternoon, sets before sunrise
Full moon	100%	14.8	Rises around sunset, sets around sunrise
Waning gibbous	100 to 50%	14.8 to 22.1	Rises after sunset, sets after sunrise
Last quarter	50%	22.1	Rises around midnight, sets around midday
Waning crescent	50 to 0%	22.1 to 29.5	Rises before sunrise, sets before sunset

One full moon, twelve clocks

A worked run of the time zone step. Take a full moon at 4:12 AM UTC on a July night, when the northern zones are on daylight saving time and Sydney is on standard time. The calculator converts the same instant like this; the last column says whether the calendar date moves.

Time zone	Offset	Local time	Calendar date
Hawaii (HST)	-10:00	6:12 PM	Day before
Alaska (AKDT)	-8:00	8:12 PM	Day before
Pacific (PDT)	-7:00	9:12 PM	Day before
Arizona (MST)	-7:00	9:12 PM	Day before
Mountain (MDT)	-6:00	10:12 PM	Day before
Central (CDT)	-5:00	11:12 PM	Day before
Eastern (EDT)	-4:00	12:12 AM	Same day
UTC	0:00	4:12 AM	Same day
UK and Ireland (BST)	+1:00	5:12 AM	Same day
Central Europe (CEST)	+2:00	6:12 AM	Same day
India (IST)	+5:30	9:42 AM	Same day
Sydney (AEST)	+10:00	2:12 PM	Same day

Six of the twelve clocks put this full moon on the evening before. Two websites that "disagree" about the date of a full moon are usually just set to different zones.

Less obvious things the cycle does

The orbit and the cycle are different lengths. The Moon goes around the Earth in 27.322 days, but the Earth moves along its own orbit meanwhile, so the Moon needs about two more days to line up with the Sun again. Phases repeat every 29.53 days on average, not every 27.

Some cycles are long, some short. Because the orbit is elliptical and the Sun tugs on it, one new moon to the next ranges from 29.26 to 29.80 days. A calendar that simply adds 29.53 days misses some phases by up to about 18 hours over these two centuries, often enough to land them on the wrong date.

February never gets a Blue Moon. In the sense NASA uses, a Blue Moon is the second full moon in one calendar month. With about 29.5 days between full moons, two fit only into a 30- or 31-day month, and on average one comes every 2.5 years. When it happens, the calculator flags it under the month table.

The lit share is not a clock. Halfway in time between new moon and first quarter, the disk is not 25% lit but well under it, because the lit share follows the angle between the Sun and the Moon as seen from the Earth. The percentage in the result is computed from that angle, not from the Moon's age.

Reading what comes back

Each part of the result answers a different question. The table also says how far each figure can be trusted.

Figure	What it tells you	How exact
Phase name	Principal phase if it falls on that day in your zone, otherwise the stretch you are in	Exact by the calendar rule
Lit percentage	Share of the visible disk lit at the chosen hour	Within 1 point of USNO in 30 test dates
Moon age	Days since the last new moon	To about a tenth of a day
Phase times	Exact instants of new, quarter and full moons, on your clock	Within 2 minutes of the Espenak catalog
Dates far in the past	Daylight saving uses today's rules for every year	Check the hour near a DST change
Planting note	Waxing or waning guideline from The Old Farmer's Almanac	Folklore, studies disagree

Nothing here predicts weather, tides at your beach or moonrise at your address; those depend on your exact location.

Moon phase questions with plain answers

What moon phase was it on the day I was born?

Enter the birth date, the time zone of the birthplace and the hour closest to the birth. Any date in the twentieth or twenty-first century works. If a principal phase fell that day, the result names it and gives its exact time; otherwise it names the stretch, such as waxing gibbous, with the lit share.

Why does the full moon look full for two or three nights?

Near full moon the lit share changes slowly. A day before or after the exact instant the disk is still lit above 95%, which the eye cannot tell from 100%. The full moon itself is a single instant, and the result gives it to the minute.

Is the phase different in Australia?

The phase and the lit share are the same everywhere at the same instant. Only the clock time and, sometimes, the date change. What does differ is the view: as NASA puts it, from the other hemisphere the Moon is in the same phase but appears upside down compared with what you are used to.

Does planting by the Moon work?

The Old Farmer's Almanac keeps the tradition: crops that bear above ground while the Moon waxes, root crops, bulbs and perennials while it wanes. The Almanac itself says some studies hint at a small effect and others call it folklore. It also reminds readers that soil quality, sunlight, water, weather and the plant variety influence growth considerably, so the Moon is one factor among many.

Why only these two centuries?

Phase times are computed in the uniform time astronomers use and then converted to clock time with Delta T, the slowly growing gap caused by the Earth's uneven rotation. For the current century the Espenak catalog uses 64 to 128 seconds, but the uncertainty grows quickly beyond that range, so the calculator stays inside the years it was checked against.

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What is the moon phase tonight in New York?

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