The Moon on the day I was born

Your date, time and place are turned into universal time with the clock rules of that place and year (historic time zones and summer time included). If you don't know the time, we use 9 PM local time and say so on the picture.

The shape comes from the angle between the Moon and the Sun along the ecliptic (0–360°) and the lit fraction of the disc. The edge between light and dark is an ellipse whose width matches the percentage exactly. The value is kept to one decimal and shown as a whole number.

The tilt is the direction from the Moon toward the Sun on your own sky. That is why the same Moon leans differently in Seoul and in Sydney. The southern hemisphere needs no special rule; it falls out of the same geometry.

The Moon's height in the painting is its altitude at that minute: the roofline is 0°, the top of the sky is 90°. If the Moon was below the horizon, the sky is left empty and the Moon is drawn faintly, in a dashed outline, under the ground, with the time it rose or set that day; one tap shows the hour it stood highest. Its size follows its distance: the nearest Moon is drawn about 14% wider than the farthest.

The sky is chosen by the Sun's altitude at that minute: day above the horizon, a dusk wash between 0° and −6°, night below that. A daytime Moon is drawn paler, as it really looks.

A calendar day (local midnight to midnight) is named new, first quarter, full or last quarter only if that exact instant falls inside it. Otherwise it is a waxing crescent, waxing gibbous, waning gibbous or waning crescent. So a 99.8% Moon is still “waxing gibbous” when the full instant comes the next day.

“N of every 100 days” counts all 36,525 days from 1950 to 2049 with the same rule. New, first quarter, full and last quarter are about 3.4% each; the four in-between names about 21.6% each.

The distance rank compares your Moon with every day of those 100 years (nearest 356,501 km, farthest 406,700 km). “Closer than 50% of days” means the Moon was nearer than on half of them.

Moon age is the number of days since the latest new Moon. The Korean lunar date comes from a table that follows the Korea Astronomy and Space Science Institute calendar; lunar January 15 and August 15 are the festivals Jeongwol Daeboreum and Chuseok.

The strip shows the Moon on 20 birthdays, from the year you were born to 19 years later, at the same clock time and place. If you were born on February 29, the years without that date stay empty.

Nineteen years is almost exactly 235 lunar months (the Metonic cycle), so the Moon on your 19th birthday nearly repeats your birth Moon. Leap days shift it by up to about a day: the Moon of May 17, 1990 was 6° off on May 17, 2009.

“Same Moon on your birthday again” is the first birthday with the same phase name and a lit fraction within 5 points.

This is an astronomical calculation. The real sky depends on weather and terrain. It is not astrology and has no meanings or fortunes.

We cannot know whether it was cloudy, or how bright the city was. The reddening of a low Moon is not simulated either: the Moon here is always the same cream colour.

Dates from 1920 to 2049 only. Clock rules before 1970 follow the IANA time zone database; where there was no standard time yet, local mean time is used and noted.

On quarter days our phase name can differ from the US Naval Observatory's: USNO names the day by its noon shape, we name it by whether the instant falls inside the day.

Your date, time and place are used only on this device. They are never put in the address bar or sent to analytics. Only the link you send or copy yourself carries them, so the person who opens it sees the same Moon.