Moon phase simulator: drag the Moon round the Earth and see its phase, tithi, age and rise time

What it does

The Moon makes no light of its own. The Sun always lights the half of it that faces the Sun, and as the Moon travels round the Earth once a month we see different amounts of that lit half. That is all the phases are: not the Earth’s shadow, just our changing view.

This page shows the same moment two ways. The top picture looks down on the Earth and Moon from far above the North Pole, with sunlight coming from the left. Drag the Moon round its orbit and the second picture shows how its face looks from the Earth that night: a thin crescent, a half Moon at first quarter, a round full Moon, then shrinking back. Under it you get the phase name, how much of the face is lit, the Moon’s age in days, the tithi and paksha of the Indian lunar calendar, and roughly when it rises and sets.

It follows Class 8 Science, keeping time with the skies (phases of the Moon, the lunar month, tithis and the Indian calendar), and helps with Class 6 and 7 work on the Moon and with eclipses later on. To find the Moon in tonight’s real sky, open Sky tonight; for why the Moon and planets move as they do, try kepler orbits; and to see dark, Moon-free nights through the year, the dark-sky calendar.

How to use it

1. Choose a Level. Class 8 shows the phase, age, tithi and rise time. Class 9 to 12 adds the lit fraction formula and why the month of phases (29.53 days) is longer than one trip round against the stars (27.32 days).
2. Drag the Moon in the top picture, move the day slider, or tap New, First quarter, Full or Last quarter. +1 day steps the Moon on by one day.
3. Seen from flips the face for the southern hemisphere, where the waxing Moon is lit on the left.
4. Under Phase on a date, pick a date and press Show this date, or press Today. The page uses the Moon’s average motion, so the real phase can be up to about half a day off.

Worked example

The page opens with the Moon 4 days old. It has gone 4 ÷ 29.53 × 360 = 48.8° round from the Sun, so it is a waxing crescent, lit on the right as seen from India. The lit part is (1 − cos 48.8°) ÷ 2 = 0.170, about 17% of the face. 48.8 ÷ 12 = 4.06, so it is tithi 5: Shukla paksha Panchami. It rose at about 09:15 and sets about 21:15 local solar time, so you see it in the west after sunset.

Pick 9 November 2026 and press Show this date: the mean age is 29.0 days, a new moon. The real new moon that day was at 07:02 UTC.

Check yourself

Five fresh questions: the Moon’s age from its angle, how much is lit, the tithi from the angle, how much later it rises after a few days, and days to the next new moon. Nothing is saved.

Tips

• A waxing Moon (growing) is seen in the evening; a waning Moon (shrinking) is up late at night and in the morning sky.
• The full Moon rises as the Sun sets, and the new Moon is up with the Sun, hidden in its glare.
• A tithi is not a day: it is the time the Moon takes to gain 12° on the Sun, so it can start at any hour and be 19 to 26 hours long.

FAQ

Are the phases caused by the Earth’s shadow? No. The Earth’s shadow only falls on the Moon during a lunar eclipse, which can happen only at full moon.

Why doesn’t every full moon give an eclipse? The Moon’s orbit is tilted by about 5° to the Earth’s, so most months it passes above or below the shadow. This page draws a flat orbit.

Are the rise times exact? No. They are for an ideal Moon on the celestial equator. Real times shift with the season, your place and the Moon’s tilted path.

Is this from the NCERT book? It covers the same topic with fibub’s own pictures and examples. fibub is not part of NCERT.

Last updated 2026-11-09.