Moon phase on any date: illumination, age and the next four phases
Pick a date and the Moon's phase, the fraction of the disc that is lit, its age in days, its distance and the four principal phases that follow, all computed.
Every figure below is computed for 12:00 UTC on the date shown, from the Moon's elongation east of the Sun. Phase instants are given in UTC.
The diameter is the geocentric one. Seen from the ground the Moon is up to 1.7% closer at zenith, which is 0.03′ — smaller than the difference between one night and the next, and the reason a quoted "supermoon" size is about the distance, not about where in the sky you look.
Next principal phases
| Phase | Instant | In |
|---|---|---|
| New moon | Nov 9, 2026 · 07:02 UTC | 139h 02m |
| First quarter | Nov 17, 2026 · 11:47 UTC | 335h 48m |
| Full moon | Nov 24, 2026 · 14:54 UTC | 506h 54m |
| Last quarter | Dec 1, 2026 · 06:09 UTC | 666h 09m |
"In" is measured from 12:00 UTC on November 3, 2026, the instant the table above describes.
The Moon’s phase is one number: how far east of the Sun it sits along the ecliptic, an angle called the elongation. At 0° it is between Earth and Sun and we see nothing; at 180° it is opposite and we see the whole disc. Everything else — the name, the percentage, the age — is that angle reported three ways.
| Elongation | Phase | Illuminated |
|---|---|---|
| 0° | New moon | 0% |
| 45° | Waxing crescent | 15% |
| 90° | First quarter | 50% |
| 135° | Waxing gibbous | 85% |
| 180° | Full moon | 100% |
| 225° | Waning gibbous | 85% |
| 270° | Last quarter | 50% |
| 315° | Waning crescent | 15% |
The percentage is (1 − cos θ) / 2, which is why the table above is not linear: a quarter moon is exactly
half lit, but the disc is 85% lit at 135° and back to 50% only at 270°.
Where the numbers come from
The tool above computes the Moon’s apparent ecliptic longitude from a truncated version of the ELP-2000/82
theory (Meeus, chapter 47), subtracts the Sun’s, and solves for the instants where that angle crosses 0°,
90°, 180° and 270°. Measured against published almanac instants for 2026, the worst error is 1.1 minutes.
That residual is printed by npm run verify-sky in the site’s own repository, and it is the reason this page
quotes phase times at all.
Two conventions worth knowing before you compare this with another site:
- The instant is UTC, not local. A full moon at 02:00 UTC is 21:00 the previous evening in New York.
- The day is not the instant. Every almanac calls the Moon full for the whole day it is closest to fullness, because a name is what a calendar needs and an instant is what an astronomer needs. A phase that falls at 23:50 does not switch names at midnight.
Reading the four figures
Age counts from the last new moon and runs to about 29.53 days. It is the fastest way to answer “is it growing or shrinking” — under roughly 14.8 days, waxing; over, waning.
Distance varies between about 356,500 km and 406,700 km because the orbit is an ellipse. It is what “supermoon” is about: a full moon near perigee is around 14% wider than one near apogee, and the apparent diameter in the panel is the honest measure of that, in arcminutes.
Elongation is the angle itself, in degrees, and the direction is the Moon’s position relative to the Sun — east of it means the lit limb is growing.
What this page will not tell you
It will not tell you what phase the Moon was in when you were born, whether a phase favours a decision, or what a full moon does to your sleep. Those are claims about people, and no ephemeris supports them.
What it will do is the thing a language model cannot: put a date and a time on a physical event, and show its working. If you want the reasoning behind the calendar rather than a lookup, start with the eight phases explained; if you want to know why the Moon is sometimes up in daylight, that has its own answer.
Times and angles on this page are computed from published algorithms, not copied from a table. They are astronomical facts, not advice.
Frequently asked questions
- Why does the tool ask for a date rather than detecting mine?
- Because the answer has to be in the page before any script runs. The default you see is the build date, computed and written into the HTML; the field is an enhancement for readers who want another day. A page whose only answer lives behind a form is a page no search engine, and no answer engine, can read.
- What does moon age mean?
- Days since the last new moon, counted along the elongation rather than the clock. The Moon's age runs from 0 to about 29.53 days, one synodic month, and it is the number that tells you whether the crescent is growing or shrinking: age under 14.8 days and the Moon is waxing, above it and it is waning.
- Why is the illumination 99% on the day before a full moon?
- Because illumination follows the cosine of the elongation, and a cosine is flat near its peak. At 170° from the Sun the Moon is 99.2% lit, at 175° it is 99.8%, and at 180° it is 100%. The last 5% of the disc takes about 19 hours to fill, which is why a full moon looks full for two or three nights.
- Is the far side of the Moon ever lit?
- Half of the Moon is lit at every moment except during an eclipse. What changes is how much of the lit half faces us. At new moon the Sun illuminates the far side and we see the unlit near side, which is why the Moon disappears rather than turning dark — it is between us and the Sun, and its lit face is pointed away.
Sources
- U.S. Naval Observatory, Astronomical Applications Department — Rise/Set/Twilight and Moon Phase tables: the published instants this site's lunar solver is checked against, agreement within 3 minutes over the 2026 lunations (aa.usno.navy.mil)
- Meeus, Astronomical Algorithms, 2nd edition, chapters 47 and 49 — the truncated ELP-2000/82 lunar theory implemented in src/lib/sky.mjs, and the 29.530589-day mean synodic month
- NASA Science — Moon: phases, illumination and the synchronous rotation that keeps one face toward Earth (science.nasa.gov/moon/)
- JPL Horizons (DE441) — the lunar ephemeris used to verify this site's right ascension, declination and distance calculations (ssd.jpl.nasa.gov/horizons/)