Moon phase for any date
What the Moon looked like on a birthday, a wedding night or the night of a story you remember, or what it will look like on a date ahead.
The Moon on
- Age
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- Elongation
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- Distance
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- Apparent size
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- Moonrise
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- Moonset
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Drawn as seen from the Northern Hemisphere: a waxing Moon is lit on the right.
How to use it
Enter a date and a local time, and pick the place it happened (or will happen) so that the time zone and the drawing are right. The Moon is drawn as it looked in that hemisphere, with the share of its disc that was lit. Day before and Day after step through the month, and Copy link gives a web address that opens this page on the same date and time, handy for a birthday card or a note in a photo album. Any date from 1900 to 2100 works.
What the numbers mean
Percent lit is the fraction of the Moon's disc in sunlight as seen from Earth. Age counts days since the last new moon; one cycle of phases takes about 29.5 days. Elongation is how far the Moon has moved ahead of the Sun along the sky's yearly path: 0° at new moon, 90° at first quarter, 180° at full and 270° at last quarter, which is how the US Naval Observatory defines the four main phases. Distance and apparent size change through the month because the Moon's orbit is an ellipse.
Accuracy
Calculations follow Jean Meeus's Astronomical Algorithms. For dates far in the past, remember that some places changed time zone or calendar rules since then.
Sources
- US Naval Observatory, Phases of the Moon and Percent of the Moon Illuminated.
- NASA Science, Moon Phases.
- Jean Meeus, Astronomical Algorithms, 2nd ed., Willmann-Bell, 1998, chapters 47–49 (Open Library record).
Questions
What was the Moon on the day I was born?
Enter your birth date, the time if you know it (evening is a good guess for what people saw) and the town or its coordinates. The phase name and drawing are what the sky showed that day.
Why is the Moon not exactly 14.8 days old at full moon?
The time from new to full moon changes by many hours from month to month because the Moon's orbit is an ellipse, so the age at full moon varies.
Does the phase depend on where I am?
The percentage lit is the same everywhere at a given moment. Only the local date, the rise and set times and which way up the Moon appears change.