Enter the day you were born and this birthday moon phase calculator renders the Moon exactly as it appeared that night. Not a diagram or a shaded circle: the real lunar surface, lit from the angle the Sun was actually at, with the craters along the terminator throwing the shadows they threw on that day.
It works for any date between 1900 and 2100, so it also answers the day you got married, the day your child arrived, or tonight.
How the image is made
The surface comes from NASA. The colour is the Lunar Reconnaissance Orbiter’s Wide Angle Camera mosaic, built from over 100,000 photographs; the terrain is laser altimetry from LOLA, the Lunar Orbiter Laser Altimeter aboard the same spacecraft, accurate to a few metres of elevation. Both are projected once into the disc you see, and your browser lights that surface for the phase angle of your date.
That angle comes from the lunar theory in Jean Meeus’s Astronomical Algorithms, the same series professional planetarium software uses. It puts the Moon within a fraction of a degree of where it was, which matters more than it sounds: the Moon moves about 12 degrees a day, so an approximation that is off by half a day draws a visibly different Moon.
Two details give the render away as real rather than drawn. The full Moon is flat, edge as bright as the middle, because lunar dust scatters light back toward its source instead of spreading it evenly. And the line between light and dark is not a clean arc. It is rough, because it falls across crater rims.
What the tool tells you
- The phase and how much was lit. Given to a tenth of a percent, which is the level at which “full moon” and “nearly full” stop being the same thing.
- The Moon’s age. Days since the new moon that started the cycle. A lunar month runs 29.5 days on average, though it varies by about half a day either way.
- How far away it was. The orbit is an ellipse, so the distance swings between roughly 356,500 km and 406,700 km. A full moon at the near end is a supermoon; at the far end, a micromoon.
- Its traditional name. One of the twelve traditional full moon names – the Wolf Moon, the Sturgeon Moon, the Harvest Moon and the rest – with blue moons and the years the Harvest Moon slides into October handled properly.
- When your Moon comes back. The years your birthday falls on the same phase again.
What each Moon phase was actually doing in the sky
A phase is not just a shape. It fixes when the Moon rose, how long it stayed up and where the shadows fell, and those are the same for that phase in any year. Here is what each one was actually doing overhead, with the old folklore reading at the end of each, for anyone who wants it.
New Moon
A new moon rises and sets with the Sun, so it crosses the sky only in daylight and never at night. It disappears not because it isn’t there, but because its lit side faces entirely away from Earth. It’s the only phase that can produce a solar eclipse, when its disc passes directly in front of the Sun’s. Tradition read this as a beginning, made before anything shows.
Waxing Crescent
A waxing crescent hangs low in the west just after sunset and sets a few hours later, gone before most evenings are over. This is the easiest phase to catch earthshine: the rest of the disc glowing faintly grey, lit by sunlight reflecting off Earth. Tradition read this thin, early light as quiet commitment, made before an idea has anything to show for itself.
First Quarter
A first quarter moon rises around midday, stands highest right at sunset, and sets close to midnight, exactly half its disc lit down a straight line. That line falls across crater rims rather than flat ground, throwing the longest shadows of the month, which makes this the best night to point a telescope at it. Tradition read the halfway split as a decision point.
Waxing Gibbous
A waxing gibbous moon is up and obvious for the entire evening, rising in mid-afternoon and not setting until after midnight. More than half its disc is lit, so craters near the terminator still throw shadows while the rest of the face washes out toward full brightness. Tradition read this stretch as refinement, the work of finishing rather than starting.
Full Moon
A full moon rises as the Sun sets, stays up the entire night, and sets again at sunrise – the only phase in the sky from dusk to dawn. It’s also the only phase that can pass through Earth’s shadow, which happens roughly twice a year and turns the disc a dim copper red. Tradition made this the loudest phase, the one every named calendar of full moons is built around.
Waning Gibbous
A waning gibbous moon rises mid-evening, after dark has properly settled, and is still hanging in the sky well into the following morning, pale against the blue daylight. Just past full, it loses a sliver more each night, though the difference is hard to see by eye until several days have passed. Tradition read this stretch as teaching, passing along what the full moon just showed.
Last Quarter
A last quarter moon rises around midnight, climbs highest right at sunrise, and is still half lit and visible well into the morning sky. The shadows along its terminator run as long as first quarter’s, but they fall across the opposite side of every crater, so familiar features look different. Tradition read this half as the letting-go point, the finish rather than the start.
Waning Crescent
A waning crescent is a thin arc low in the east just before dawn, up for only an hour or two before sunrise erases it. Earthshine often fills in the rest of the disc with a faint grey glow, sunlight bounced off Earth and back onto the Moon’s dark side. Tradition gave this last sliver to the quiet end of things, right before the cycle starts over.
The traditional full moon names
The names come from a mix of Colonial American, European and Native American sources, collected and popularised by the almanacs. They belong to the full moon of each month:
- January – Wolf Moon. Named for wolves heard more often in midwinter.
- February – Snow Moon. The heaviest snowfall month across much of the northern United States.
- March – Worm Moon. For the casts that appear as the ground thaws.
- April – Pink Moon. For creeping phlox, not for the Moon’s colour.
- May – Flower Moon.
- June – Strawberry Moon. The short picking season in the northeast.
- July – Buck Moon. When new antlers push through.
- August – Sturgeon Moon. For the Great Lakes fishery.
- September – Harvest Moon. Usually. See below.
- October – Hunter’s Moon.
- November – Beaver Moon.
- December – Cold Moon.
The Harvest Moon breaks the month-by-month pattern, and that’s why so many lists of these names are subtly wrong. It isn’t September’s full moon by definition. It’s the full moon that falls nearest the autumn equinox, and that happens to land in October roughly one year in three. When it does, September’s full moon reverts to its older name, the Corn Moon, and the Hunter’s Moon slides to November. The calculator above works this out from the actual equinox date for your year, rather than reading it off a fixed table.
Frequently asked questions
What was the moon phase when I was born?
The Moon phase on your birthday depends on your exact date of birth: the lunar cycle runs about 29.5 days, roughly 11 days short of the calendar year, so the phase on your birthday shifts every year and rarely repeats until the Metonic cycle brings it back around. Enter your date of birth into the calculator at the top of this page for the exact phase, illumination percentage, Moon age and traditional name for that night.
Do I need to know my time of birth?
You don’t need your exact time of birth for an accurate Moon phase, because the Moon only moves about 3% of a phase in twelve hours. The tool uses midday if you leave the field blank. Add your birth time if you know it and want the precise rendering.
Does where I was born matter?
Your birthplace doesn’t change your Moon phase, because everyone on Earth sees the same fraction of the Moon lit at the same moment. What changes with location is orientation: north of the equator a waxing Moon is lit on the right, south of it the same Moon looks lit on the left. Use the hemisphere setting to match that.
Why is my Moon not perfectly full when I was born on a full moon?
A full moon lasts only an instant, not a full day, so a birth even twelve hours either side of that instant renders at about 99.5% lit rather than 100%. The Moon is exactly full for a moment and then starts waning immediately. It reaches a true 100% only during a lunar eclipse, when it sits inside Earth’s shadow.
How often does my birthday get the same Moon again?
Your birthday lands on very nearly the same Moon phase every 19 years. That’s the Metonic cycle: 235 lunar months come within about two hours of 19 solar years, a relationship the Greek astronomer Meton of Athens worked out in the fifth century BC and which still sets the date of Easter today.
Can I use the image?
The download button gives you a portrait card sized 1080 by 1350 pixels, built for Instagram and other story and feed formats. The lunar imagery underneath it comes from NASA and is public domain, so the image itself is free to reuse.
Why has the moon phase birthday trend taken off online?
The moon phase birthday trend spread on TikTok and Instagram as a way to turn a fixed astronomical fact into shareable personal trivia, with the same appeal as a birth flower or a birthstone. Posting your exact Moon phase, illumination percentage and traditional full moon name works because everyone’s version is different and nobody can fake it. The download card above is sized in portrait for exactly that kind of post.
Is the Moon actually grey?
The Moon is grey, and darker than it looks against the black sky: lunar soil reflects only about 12% of the sunlight that hits it, roughly the same reflectivity as worn asphalt. It reads as bright white only because there’s nothing nearby to compare it to.
If you want more of the Moon: read 10 unique characteristics of the Moon, work out what you would weigh standing on it, or go through the missions that landed there. You can also see how far away every planet is right now and how long it would take to travel there. There is also a daily astronomy word search and a daily mini crossword if you would rather play something.
Lunar colour and elevation maps courtesy of NASA’s Scientific Visualization Studio, built from Lunar Reconnaissance Orbiter data.