Prints
The Moon on your day
Pick a day: a birthday, a wedding day, a day you want to remember. The plate shows the Moon at 12:00 local time in your time zone (your browser’s by default; you can change it).
What is on the plate
- The Moon as it looked that day, with the lit part in cream and the dark part in blue.
- The phase in words, how much of the disc is lit, how many days old the Moon is (since the last new moon) and the zodiac sign it stands in.
- The dates of the next new moon and the next full moon.
How it is calculated
The positions of the Sun and the Moon come from the formulas in Jean Meeus’s Astronomical Algorithms, calculated in your browser. We check them against our own engine, which uses NASA’s JPL ephemeris: new and full moons agree to within three minutes.
The Moon is drawn as seen from the northern hemisphere (in the south it looks upside down). The plate shows the Moon at 12:00 in the time zone you choose, with daylight saving time taken into account; the dates of the next new and full moon are in that time zone too.
Nothing leaves your browser
The date and the time zone you choose stay in your browser: the plate is calculated and drawn there, without any request to our server. We count only which kind of file was saved (for example ‘PNG’), never the date or the time zone.
Sources
- Jean Meeus, Astronomical Algorithms (Willmann-Bell, 1991; second edition 1998): the formulas for the Sun and the Moon. en.wikipedia.org
- Park, R. S. et al., ‘The JPL Planetary and Lunar Ephemerides DE440 and DE441’, The Astronomical Journal 161, 105 (2021): the ephemeris of our own engine, used to check the formulas. doi.org
- Brandon Rhodes, Skyfield (MIT licence): the programme of our own engine. rhodesmill.org
This page was written from the sources above. Where they disagree, we say so; claims we could not confirm are left out.