Moon phase calendar

Pick a city and you get the whole month, night by night: the phase, how much of the disc is lit, when the Moon rises and sets, where it will be in your sky, how far away it is and how large it looks. Ask for a single moment instead and you get that one, with a card to share. Free, no account, nothing stored.

What it does, and why it is here

“Full moon on the 12th” is a fact about the planet. Whether you will see it, and where to point, is a fact about your latitude, your longitude and your clock — and those are what a phase calendar usually leaves out.

The Moon rises about fifty minutes later each day, so its position at a given hour drifts right across the sky over a month. A full moon rises at sunset and is up all night; a waxing crescent sets in the early evening and is gone before it is properly dark. Knowing the phase without knowing the rise time answers half the question.

So this page gives the phase and the geometry, in your city’s own local time: when it comes up, when it goes down, how high it climbs, which bearing it sits on. And because a lot of people looking up the Moon are about to photograph it, it will also tell you how large it comes out on the lens you own.

What you fill in

• City — type and pick; the coordinates and the time zone follow. Every time in the answer is that city’s local time.
• The month’s calendar — this month or the next.
• Or a precise moment — any date and time, for the state of the Moon exactly then. That answer carries a card you can share.
• In the lens, optional — a focal length and a sensor format, and the answer says how large the Moon comes out in the frame. Add the resolution in megapixels and it gives the disc in pixels.

What you get back

For each night of the month, one row:

• Phase and its glyph, with the traditional name where the night has one.
• Illumination — the percentage of the disc lit, which is the number that actually matters for astrophotography, where 30% is a very different night from 70%.
• Moonrise and moonset, in local time. Some rows have a dash: on roughly one day a month the Moon does not rise, or does not set, inside the calendar day — a consequence of the fifty-minute drift, not a missing value.
• Elevation and azimuth — how high and on which bearing, so you know whether it will clear the buildings.
• Distance and apparent diameter — the Moon’s orbit is an ellipse, and the disc is measurably larger at perigee than at apogee.
• Notes, where a night carries something worth flagging.

And the Moon in the lens, when you gave one: how much of the frame the disc fills at your focal length and sensor, in pixels if you gave the resolution. This is the answer to the disappointment everyone has once — the Moon is half a degree across, so at 200 mm on full frame it is a bright dot, and it takes 600 mm and up before it fills anything.

What it does not do

No weather. A clear-sky calendar is a different problem, and this one only knows where the Moon will be, not whether you will see it.

It assumes a flat horizon, so a hill or a building to the east delays moonrise by minutes the tool cannot know about. And it does not predict eclipses: those need the Moon at a node as well as at a phase, which is a separate calculation.

Reading the eight phase names

The right-hand column is the one worth internalising: waxing means evening sky, waning means morning sky. For dark-sky photography you want the days around new moon, or the waxing crescent nights where it sets before you start.

Questions

Is it free?

Yes. No account, no key, no limit.

Do you keep what I search for?

No. The city and date are used to compute and then forgotten.

Which months can I ask for?

The calendar serves the current month and the next. A single moment can be asked for at any date.

Why does a row have no moonrise?

Because the Moon rises about fifty minutes later each day, so about once a month a calendar day passes without a rise, or without a set. The dash is correct, not missing.

Why is my village missing from the list?

The list holds cities; pick the nearest. A few kilometres change the times by seconds.

What does a negative elevation mean?

The Moon is below the horizon at that moment — up, but not from where you are standing.

Why can I sometimes see the Moon in broad daylight?

Because it is only near the Sun in the sky at new moon. At first quarter it rises at midday, which puts it in a blue sky for the whole afternoon.

What lens do I need to photograph it?

Fill in the lens fields and the answer tells you exactly. As a rule: 400 mm gives a recognisable disc on full frame, 600 mm and above gives one worth cropping into.

Why do we always see the same face?

The Moon rotates once per orbit — tidally locked. A slight wobble called libration reveals a little more than half of the surface over time.

Sources and further reading

• Lunar phase — the eight names and the geometry behind them.
• Orbit of the Moon — why the distance and the apparent size change.
• Libration — the wobble that shows more than half the surface.