What phase was the moon on my birthday?
Type the date. The answer appears as you type: phase, % lit, age and the real face.
Showing an example, 1 January 2000. Type your own date over it.
- The phase is the same worldwide at any instant; the tilt is not. The picture is the view from the northern hemisphere, lit on the right while waxing. From Australia or Argentina it hangs upside down.
Nothing is uploaded. The date stays in this page; the Moon is computed on your device with the same astronomy engine as the Polyatic star map and moon poster. Free, no account.
Reading the three numbers
The phase name says where the Moon was in its monthly cycle: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent. The four principal names are given only within about 14 hours of the exact moment, so most birthdays fall in one of the four in-between spans. Illuminated is the share of the visible disc that sunlight reached, from 0% at new moon to 100% at full. Moon age counts the days since the last new moon; a full cycle averages 29.53 days, so an age near 14.8 means close to full and an age near 22 means a half moon in the morning sky.
A worked example: 14 February 2001 at 21:00 UTC was a Last Quarter moon, 53% lit and 21.3 days old. At the first minute of that day it was still a waning gibbous at 62%; by midnight it had crossed the quarter. That is the busiest kind of day, because near the quarters the lit share falls or rises by up to about 10 points in 24 hours.
Does the hour or the place of birth matter?
The hour moves the percentage, not usually the name. Between noon and midnight the figure shifts by a few points at most, and next to a new or full moon it barely moves at all. Under the date box the page states how much it changed across your whole birth day, so you can see whether the hour matters for yours. Without a time it reads 21:00 on this device's clock, the same default the poster uses.
The place does not change the phase: at any instant the Moon is equally lit for everyone. It can change the date, though. A baby born at 23:00 in New York arrived at 04:00 the next morning in London, so if you were born far from where you are now and near midnight, set the clock to the time it would have been here. The tilt also differs: from the southern hemisphere the lit side is on the left while the Moon is waxing. The poster turns the disc for a named town; this answer page shows the textbook northern view.
Your birthday moon comes back every 19 years
235 lunar months last 6,939.69 days and 19 calendar years last 6,939.60 days, a gap of about two hours. So on your 19th, 38th and 57th birthdays the Moon is in nearly the same phase it was when you were born, give or take a day as leap years fall. Astronomers call this the Metonic cycle; it is why the date of Easter follows a 19-year pattern. There is a looser 8-year echo too (99 lunar months against 8 years), about a day and a half off.
Where the numbers come from, and the limits
The Sun and Moon positions follow Jean Meeus' Astronomical Algorithms, the same code that draws the Polyatic star map, so the percentage is good to well under one point for any date from the year 1000 to 2999. The face is NASA's Lunar Reconnaissance Orbiter map, lit to the computed phase. The small monthly wobble called libration is not drawn, and nothing here knows whether it was cloudy that night.