Moon Phases, Lunar Months and What You Can Observe
Why the Moon changes its appearance, why a lunar month is about 29.5 days, and how phases relate to tithi without being identical.
The geometry of a phase
The Moon reflects sunlight; it does not produce visible light of its own. About half of the lunar sphere is illuminated at most times. As the Moon orbits Earth, our viewing angle changes, revealing different portions of that sunlit half. That is why we see crescents, quarters and the full Moon.
A phase is not caused by Earth’s shadow, except during an actual lunar eclipse. In a new Moon, the sunlit side faces mostly away from us; near full Moon, most of the sunlit side is visible. Eclipses require an additional alignment because the Moon’s orbital plane is tilted relative to Earth’s path around the Sun.
Two lunar clocks
The Moon returns to approximately the same direction among the stars in about 27.3 days, a sidereal month. But the Earth–Moon system is also moving around the Sun, so the interval from one new Moon to the next is longer: on average about 29.5 days. That is the synodic month underlying the familiar cycle of phases.
The traditional tithi divides the changing Moon–Sun longitude separation into thirty steps of 12° each. It is related to the phase cycle, but each tithi has its own start and end moment, whereas an observational label such as waxing crescent describes a broader visual appearance. Do not treat “tithi number” and “phase name” as interchangeable.
Check the sky from your location
A full Moon generally rises around sunset and sets near sunrise. A first-quarter Moon is often conveniently visible in the evening, while a waning crescent is usually easier to see before dawn. Exact appearance, rise times, weather and visibility depend on your location and date. A universal calendar date is not enough to promise an observable event.
For a useful routine, note the phase, Moon rise or set and your city, then check the real sky. Panchanga can supply lunar calendar context; it should not claim to predict local cloud cover. Keep astronomy measurements and traditional symbolic readings distinct even when you explore them on the same page.
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Sources and methodology
References for checking the astronomical and calendrical facts in this guide. Traditional interpretations are not astronomical measurements.