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Moon phases

Why the Moon looks full for several nights

The full Moon is a single instant, yet the Moon looks round for several evenings. See how the lit fraction changes, and where Purnima tithi fits.

01 · Nights around the full Moon

The full Moon is one instant; full-looking nights are several.

How much of the Moon is lit changes slowly near full, so for three or four evenings in a row the Moon looks round. Purnima, the tithi ending at the exact full Moon, lasts less than a day. Follow the nights around 26 October 2026.

The Moon at 21:00 IST on the nights around the full Moon of 26 October 2026 Seven Moon discs, one for 21:00 IST each night from 23 to 29 October 2026. From 24 to 27 October the Moon is more than 96 percent lit and looks full each evening. The exact full Moon falls at 09:41 IST on 26 October, in daylight in India, and ends Purnima tithi. 25 Oct, 21:00: 99.5 percent lit, Shukla Purnima. 21:00 IST EACH NIGHT · PERCENTAGE OF THE DISC LIT 23 Oct92.0%Trayodashi24 Oct96.9%Chaturdashi25 Oct99.5%Purnima26 Oct99.5%Pratipada27 Oct96.8%Dvitiya28 Oct91.5%Tritiya29 Oct83.8%Chaturthi TITHIS, 22 TO 30 OCTOBER · LINES: DELHI SUNRISE DvadaTrayoChatuPurniPratiDvitiTritiChatu Full Moon 26 Oct 09:41
25 Oct, 21:0099.5% of the disc lit · Shukla Purnima
Lit fraction from the angle between the Sun and Moon seen from Earth’s centre, from the site’s ephemeris. The Moon was about 4½° from the ecliptic, so it never reached a perfect 100%.

02 · A flat top

Near full, the light hardly changes.

Over a whole lunar month the lit fraction rises and falls along a smooth curve. Its top is broad: a day either side of full changes it by only a few percent.

How much of the Moon is lit through one lunar month The lit fraction of the Moon from the new Moon of 10 October 2026 to the next on 9 November. Near full, the curve is flat: the Moon stays more than 95 percent lit for about 3.8 days, from 24 Oct, 11:20 to 28 Oct, 06:20, while Purnima tithi lasts under a day. Purnima tithi 0%25%50%75%100% Over 95% lit 10 Oct15 Oct20 Oct25 Oct30 Oct5 Nov
From the new Moon of 10 October to that of 9 November 2026, from the site’s ephemeris.

A phase is an angle

The Sun always lights half of the Moon. How much of that lit half faces Earth depends on the angle between the Sun and Moon as seen from Earth. At new Moon the angle is near 0° and almost none of the lit half faces us; at full Moon it is near 180° and almost all of it does. The tithi counts the same angle in 12° steps.

The full Moon is the instant the Moon’s longitude is exactly 180° from the Sun’s. In October 2026 that instant came at 09:41 IST on 26 October, in daylight in India.

A flat top

Near full, the lit fraction changes slowly. Measured with the site’s ephemeris, the Moon was more than 95% lit for about 3.8 days around that instant, from late morning on 24 October to early morning on 28 October. At 21:00 IST it was:

Evening Lit Tithi at that time
24 October 96.9% Shukla Chaturdashi
25 October 99.5% Purnima
26 October 99.5% Krishna Pratipada
27 October 96.8% Krishna Dvitiya

To the eye, all four look full. The difference of a few percent is a thin unlit edge that is hard to see without a telescope.

The Moon never quite reaches 100% that month, because it was about 4½° north of the ecliptic, so the alignment with the Sun was not exact. When it is exact enough, the full Moon passes through Earth’s shadow: a lunar eclipse, as why there is no eclipse every month explains.

Purnima is a span, not the instant

Purnima is the fifteenth tithi of the waxing fortnight. It covers the last 12° before full and ends at the full-Moon instant. In October 2026 it ran from 11:56 IST on 25 October to 09:41 on 26 October, less than a day. The evening of the 25th fell within it; the evening of the 26th, though the Moon looked just as full, was already in Krishna Pratipada.

So Purnima touched two dates. The site’s list of Purnima dates shows both: 25 October, when the Moon rose that evening during Purnima and Sharad Purnima is observed, and 26 October, when Purnima was still the tithi at sunrise. Which date an observance uses depends on its own rule, such as the Moon’s rising or the tithi at sunrise. The tithi and Moon phase guide compares the two ideas.

See tonight’s Moon and today’s tithi on the Delhi Panchang, or explore another topic in Learn.