Enter the day you were born and see 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 the 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 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. The Wolf Moon, the Sturgeon Moon, the Harvest Moon and the rest, with the 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 your Moon phase means
People have read meaning into the phase they were born under for as long as they have been keeping track of it. None of this is astronomy, and none of it predicts anything. It is folklore, and it is here because it is old and people enjoy it.
New Moon
Born at the start of a cycle, with nothing lit. Tradition reads this as a beginner’s position: people who would rather start something than inherit it, and who are comfortable working before there is much to show. Nobody born under a new moon has ever seen the Moon they were born under, which is a strange thing to own.
Waxing Crescent
The first sliver, low in the west just after sunset. Folklore gives this phase to people who commit early and quietly, before an idea is obviously going to work. The crescent is also when earthshine is easiest to see, the faint grey glow filling the unlit part of the disc, which is sunlight that bounced off Earth first.
First Quarter
Exactly half lit, and the best night of the month to point a telescope at the Moon: the shadows along the terminator are long, and craters that vanish at full moon stand out sharply. The traditional reading is a decision point, and a temperament that would rather push through resistance than wait it out.
Waxing Gibbous
More than half, not yet whole. The old reading is refinement rather than invention: people who improve what already exists and notice what is still missing. This is the phase most people picture when they picture the Moon, because it is the one that is up and obvious during the early evening.
Full Moon
The whole disc lit, rising as the Sun sets. Every culture that named the phases made this one the loudest, and tradition follows: it is read as a birth under maximum visibility. Full moons are the only phase that can be eclipsed, and roughly twice a year one passes through Earth’s shadow and turns copper.
Waning Gibbous
Just past full, rising after dark. The traditional reading is teaching and passing on, the phase of someone who explains rather than announces. If you were born under one, the Moon was in the sky for most of the following morning, hanging pale in a blue daytime sky.
Last Quarter
Half lit again, the other half this time, and up in the small hours. Folklore reads it as the letting-go point, the temperament that finishes and clears rather than accumulates. The shadows are as long as at first quarter, but the lighting falls on the opposite side of every crater.
Waning Crescent
The last thin arc before dawn, and the hardest phase to catch. Tradition gives it to people who are comfortable at the quiet end of things. It is worth getting up for at least once: a waning crescent low in the east before sunrise, with the rest of the disc faintly visible in earthshine, is the best free thing in the sky.
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 is the one exception, and it is the reason most lists of these names are subtly wrong. It is not September’s full moon by definition. It is the full moon nearest the autumn equinox, which lands in October roughly one year in three. When that happens, September’s full moon takes its older name of Corn Moon, and the Hunter’s Moon moves to November. The tool above works this out for your date rather than reading it off a table.
Frequently asked questions
Do I need to know my time of birth?
No. The tool uses midday if you leave it blank, and the Moon only moves about 3% of a phase in twelve hours, so the picture barely changes. Add it if you know it and want the exact one.
Does where I was born matter?
For the phase, no. Everyone on Earth sees the same fraction of the Moon lit at the same moment. What changes with location is the 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 for that.
Why is my Moon not perfectly full when I was born on a full moon?
Because “full moon” is an instant, not a day. The Moon is exactly full for a moment and then starts waning, so a birth twelve hours either side lands at about 99.5% rather than 100%. A Moon is only ever 100% lit during a lunar eclipse, and then it is in Earth’s shadow.
How often does my birthday get the same Moon again?
Every 19 years, near enough. That is the Metonic cycle: 235 lunar months come within two hours of 19 solar years, which the Greek astronomer Meton worked out in the fifth century BC and which is still what sets the date of Easter.
Can I use the image?
Yes. The download button gives you a card at 1200 by 630 pixels. The lunar imagery underneath it is from NASA and is public domain.
Is the Moon actually grey?
Yes, and darker than it looks. Lunar soil reflects about 12% of the light that hits it, roughly the same as worn asphalt. It only reads as bright white because it is sitting against a black sky.
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. 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.