Birthday moon
What moon phase was I born under? How it is worked out
By Toheed MehmoodReviewed How we check facts
In short
The phase depends on the angle between the Sun and the Moon as seen from Earth, which repeats every 29.5 days. The calculator works out that angle for midday on your date. On 20 July 1969, the day of the first Moon landing, the Moon was a waxing crescent, about 30% lit.
- Lunar cycle
- About 29.5 days
- Phases
- 8
- Full moons a year
- 12 or 13
How to find your birthday moon
- Enter your date of birth, or any other date.
- See the phase name, a drawing of the Moon and the share of it that was lit.
- Check whether it was waxing (growing) or waning (shrinking), and when the next full moon came.
The eight phases of the Moon
- New Moon
- The Moon is between Earth and the Sun, and the side facing us is dark.
- Waxing Crescent
- A thin sliver of light grows on the right (in the Northern Hemisphere).
- First Quarter
- Half the disc is lit, about a week after the new moon.
- Waxing Gibbous
- More than half lit and still growing.
- Full Moon
- The whole face is lit, about two weeks after the new moon.
- Waning Gibbous
- More than half lit and shrinking.
- Last Quarter
- Half lit again, on the opposite side, also called third quarter.
- Waning Crescent
- A thin sliver before the next new moon.
How accurate is it?
The calculator uses the standard astronomical formulas from Jean Meeus's “Astronomical Algorithms” for the Sun–Moon angle, which match published phase times to within a fraction of a degree. The Moon's angle changes by about 12° a day, so the phase name is reliable for a date.
The four main phases (new, first quarter, full, last quarter) are exact moments. Each is named for the date within about a day of it. If you were born at night near one of those moments, the phase at your birth time may have been one step either side.
Does the phase change by country?
No. Everyone on Earth sees the same phase at the same moment. What changes is the view: in the Southern Hemisphere the Moon appears upside down compared with the Northern Hemisphere, so a waxing crescent is lit on the left instead of the right.
Common questions
What moon phase was I born under?
Enter your date of birth above. The calculator shows the phase that day, how much of the Moon was lit and whether it was waxing or waning.
How long is a full lunar cycle?
About 29.5 days from one new moon to the next. NASA notes that one orbit takes about 27.3 days, but the phases take longer because Earth moves around the Sun at the same time.
Is the moon phase the same everywhere on Earth?
Yes. The phase is the same worldwide at any moment, though the Moon looks flipped in the Southern Hemisphere.
Does it need my birth time?
No. It uses midday on your date. Only people born within a day of an exact new, quarter or full moon might see a different name at their birth time.
What are the eight moon phases?
New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter and Waning Crescent.
Can I check the moon phase for any date?
Yes. Enter any date, past or future, to see the phase, how much of the Moon was lit and the next full moon.
Sources
- Moon phases · NASA Science
- Moon pairs and the synodic month · NASA Astronomy Picture of the Day