Moon phase calendar

The Moon never changes shape — we just see different amounts of its sunlit half as it circles Earth. The four principal phases are exact moments; the four in between are stretches of about a week. Because the Moon's position relative to the Sun sets the phase, it also sets when the Moon is up.

One row per lunation (new moon to new moon). Times are UTC; add 5 h 30 m for India, subtract 4–5 h for New York. Grey dates fall outside 2026–2027 and are shown to complete the cycle.

Quarters aren't spaced exactly 7.38 days apart. The Moon's orbit is an ellipse, so it moves faster near perigee and slower near apogee. In the table above, the gap from new moon to first quarter ranges from about 6.6 to 8.2 days. Whole lunations vary too, from about 29.27 to 29.83 days, which is one reason lunar calendars can't simply alternate 29- and 30-day months forever without correction.

From the northern hemisphere a waxing moon is lit on the right and a waning moon on the left. A handy memory aid is "DOC": the waxing moon is shaped like a D, the full moon an O, and the waning moon a C. South of the equator the picture is flipped left to right, because observers there face north to see the Moon. Near the equator, including much of India, the crescent tips over and lies on its back, like a boat or a smile — the shape that appears in many flags and emblems.

The Hindu calendar counts the Moon's phase precisely: a tithi is the time the Moon takes to gain 12° on the Sun, so there are 30 tithis in a lunar month — 15 in the bright fortnight (Shukla paksha, new to full) and 15 in the dark (Krishna paksha, full to new). Amavasya is the new moon, Purnima the full moon, and Ashtami falls at the quarters. Because the Moon's speed varies, a tithi lasts anywhere from about 19 to 26 hours and doesn't line up with sunrise-to-sunrise days, which is why a tithi can be "skipped" or "repeated" in the almanac. The calendar above shows the tithi at noon for any day you tap.

The phases are not caused by Earth's shadow. The dark part of a crescent is simply the Moon's night side facing us. Earth's shadow only falls on the Moon during a lunar eclipse, which can happen only at full moon — and only when the full moon is near one of the two points where the Moon's tilted orbit crosses Earth's, which is why we don't get an eclipse every month.