Astronomical & visual time
Moon phase tracker
See tonight's moon at a glance — its phase, how much of the disc is lit, and when the next full and new moons arrive. Computed from the lunar cycle, right in your browser.
Phase is computed from the synodic month and shown for your local date. Illumination is the fraction of the moon's disc lit by the sun.
How to use the moon phase tracker
Look at tonight
The current phase is drawn as it appears, with the illuminated fraction and the moon's age in days since the last new moon.
Find the next principal phase
New, first quarter, full and last quarter are listed with their dates, so you can see where in the cycle you are.
Check the illumination number
Percentage illuminated is what matters for practical purposes — a 60% moon is bright enough to walk by and bright enough to wash out faint stars.
Plan around it
For dark-sky observing, aim for the days around new moon. For moonlit landscapes, aim for full.
The lunar cycle, and what the phase actually tells you
The moon takes 29.53 days to return to the same phase — the synodic month. That is longer than the 27.32 days it takes to orbit Earth once, because Earth has moved along its own orbit in the meantime and the moon has to travel a little further to line up with the sun again. The difference is why a calendar month and a lunar month never quite agree.
Phases are a geometry effect, not a shadow. Half the moon is always lit; what changes is how much of the lit half faces us. This is why a lunar eclipse — where Earth's shadow genuinely falls on the moon — is a rare and distinct event rather than something that happens every month.
Which side is lit depends on where you are. In the northern hemisphere a waxing crescent is lit on the right; in the southern hemisphere it appears on the left, and near the equator it can sit like a bowl at the bottom. All three are the same moon at the same phase, seen from a differently oriented vantage point.
The phase also predicts when the moon is in the sky, which is often more useful than the phase itself. A full moon rises around sunset and sets around sunrise — up all night. A new moon is up all day and invisible. A first-quarter moon rises around noon and sets around midnight.
When you'd reach for it
Astronomy sessions
Plan deep-sky observing for the dark nights around new moon.
Night photography
Choose between a moonlit landscape and a dark sky for the Milky Way.
Fishing and tides
Spring tides follow new and full moons, when sun and moon pull together.
Camping and hiking
Know whether you will have natural light for a night walk.
Cultural and religious calendars
Many calendars are lunar; the phase marks the start of a month.
Gardening by the moon
A long-standing tradition that times sowing to the phase.
Questions & answers
- How is the phase calculated?
- From the synodic month — the ~29.53-day cycle between identical phases — measured from a known new moon. It's accurate to within a few hours, enough for the phase name, illumination, and upcoming full and new moons.
- Is the moon phase the same everywhere?
- The illuminated fraction is essentially identical worldwide at a given instant; only the moon's orientation in the sky and its rise and set times differ by location.
- What does illumination percentage mean?
- It's the share of the moon's visible disc lit by the sun — 0% at new moon, 100% at full moon.