0% to 100% in five steps
A normal waxing run climbs 0%, about 25%, 50%, about 75%, 100%; the waning half mirrors it. Estimate the lit fraction to the nearest quarter and you have the phase family.
What phase is it tonight?
You can name tonight's phase with two observations: how much of the disk is lit, and which side carries the light. A half-lit moon high at sunset is a first quarter; the same half-lit disk high at sunrise is a last quarter. Everything else — the day of the cycle, the percentage, the rise time — follows from one number: the 29.53-day synodic month.
An independent almanac of the lunar cycle
Scroll the strip sideways — 6 cards.
A normal waxing run climbs 0%, about 25%, 50%, about 75%, 100%; the waning half mirrors it. Estimate the lit fraction to the nearest quarter and you have the phase family.
The eight principal phases divide the 29.53-day month into near-equal steps. One week after new expect first quarter; two weeks, full; three weeks, last quarter.
The Moon moves about 13.2° a day while the Earth turns 360° in roughly 23 h 56 m. The difference surfaces as a moonrise about 50 minutes later each day.
First quarter stands about 90° east of the Sun and shows from noon to midnight. Last quarter stands 90° west and shows the opposite limb — the one with large craters such as Tycho.
The orbital tilt carries most new and full moons above or below the Sun–Earth line. Only when the nodes align within about 0.5° does an eclipse occur.
The Metonic cycle returns each phase to nearly the same calendar date every 19 years — the backbone of leap-month rules in some lunar calendars.
Cycle days are counted from new moon; the eight marks divide 29.53 days into steps of about 7.38.
| Phase | Days after new moon | Disk lit | Moonrise (approx.) | Best time to look |
|---|---|---|---|---|
| New | 0 d | 0% | Near sunrise | Not observable — the Moon keeps the Sun's hours |
| Waxing crescent | ≈3.7 d | ≈25% | Mid-morning | Evening twilight, low after sunset |
| First quarter | 7.38 d | 50% | Near noon | About noon to midnight |
| Waxing gibbous | ≈11.1 d | ≈75% | Mid-afternoon | Evening into the early hours |
| Full | 14.77 d | 100% | Near sunset | All night |
| Waning gibbous | ≈18.5 d | ≈75% | Mid-evening | Late evening to morning |
| Last quarter | 22.15 d | 50% | Near midnight | Midnight to dawn |
| Waning crescent | ≈25.8 d | ≈25% | Before dawn | Pre-dawn and morning twilight |
Two observations — the lit fraction and the hour you see the Moon — name any phase without an instrument.
Start with the disk. Fully lit means full; exactly half lit means a quarter; a thin sliver is a crescent; anything between half and full is a gibbous. In a normal waxing run the lit fraction climbs through five steps — 0%, about 25%, 50%, about 75%, 100% — and the waning half repeats them in mirror image.
Then read the geometry. A first quarter moon stands about 90° east of the Sun and is visible from about noon to midnight; a last quarter stands 90° west, shows the opposite half of the surface — the limb with the large craters such as Tycho — and belongs to the hours after midnight. Same 50%, different phase.
For a number rather than a name, the lit fraction is approximately (1 − cos elongation) / 2, where elongation is the Sun–Moon angle in the sky. That one formula converts any estimate of the angle into a percentage illumination.
The eight named phases divide the 29.53-day synodic month into steps of about 7.38 days.
Count from new moon: day 0 is new, day 7.38 is first quarter, day 14.77 is full, day 22.15 is last quarter, and day 29.53 is the next new. The four intermediate names — waxing crescent, waxing gibbous, waning gibbous, waning crescent — sit near the midpoints, around days 3.7, 11.1, 18.5 and 25.8.
The prefixes do real work: waxing means the lit fraction is growing toward full, waning that it is shrinking back toward new. A waxing and a waning crescent show the same roughly 25% of the disk — only the lit limb and the time of night tell them apart.
The phase-by-phase table with rise times and viewing windows lives on the companion page The Eight Moon Phases Explained (/moon-phases-explained); the condensed version appears in the table below.
Every value on these pages is taken from the Moon's own measured quantities — the 29.53059-day synodic month, the 27.32-day sidereal period, the 363,300–405,500 km distance range and the 5.1° orbital tilt — or derived from them by plain arithmetic. Where a figure is an average, such as the 50-minute daily drift, the text says so. No astrological, commercial or crowdsourced material is used.
Where the numbers come from
Rather than cite publishers, this almanac cites quantities: each claim on the page can be re-derived from the synodic month, the sidereal period, the orbital tilt and the distance range listed in the definitions.